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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>8.1 Data-structure Contracts</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewselflink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" class="tocviewlink" data-pltdoc="x">Running Racket</a></td></tr><tr><td align="right"></td><td><a href="doc-bibliography.html" class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">▼</a></td><td>8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">8.1 </td><td><a href="data-structure-contracts.html" class="tocviewselflink" data-pltdoc="x">Data-<wbr></wbr>structure Contracts</a></td></tr><tr><td align="right">8.2 </td><td><a href="function-contracts.html" class="tocviewlink" data-pltdoc="x">Function Contracts</a></td></tr><tr><td align="right">8.3 </td><td><a href="parametric-contracts.html" class="tocviewlink" data-pltdoc="x">Parametric Contracts</a></td></tr><tr><td align="right">8.4 </td><td><a href="Lazy_Data-structure_Contracts.html" class="tocviewlink" data-pltdoc="x">Lazy Data-<wbr></wbr>structure Contracts</a></td></tr><tr><td align="right">8.5 </td><td><a href="Structure_Type_Property_Contracts.html" class="tocviewlink" data-pltdoc="x">Structure Type Property Contracts</a></td></tr><tr><td align="right">8.6 </td><td><a href="attaching-contracts-to-values.html" class="tocviewlink" data-pltdoc="x">Attaching Contracts to Values</a></td></tr><tr><td align="right">8.7 </td><td><a href="Building_New_Contract_Combinators.html" class="tocviewlink" data-pltdoc="x">Building New Contract Combinators</a></td></tr><tr><td align="right">8.8 </td><td><a href="contract-utilities.html" class="tocviewlink" data-pltdoc="x">Contract Utilities</a></td></tr><tr><td align="right">8.9 </td><td><a href="racket_contract_base.html" class="tocviewlink" data-pltdoc="x"><span class="RktModLink"><span class="RktSym">racket/<span class="mywbr"> </span>contract/<span class="mywbr"> </span>base</span></span></a></td></tr><tr><td align="right">8.10 </td><td><a href="collapsible.html" class="tocviewlink" data-pltdoc="x">Collapsible Contracts</a></td></tr><tr><td align="right">8.11 </td><td><a href="Legacy_Contracts.html" class="tocviewlink" data-pltdoc="x">Legacy Contracts</a></td></tr><tr><td align="right">8.12 </td><td><a href="Random_generation.html" class="tocviewlink" data-pltdoc="x">Random generation</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-with-explanation%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">flat-<wbr></wbr>contract-<wbr></wbr>with-<wbr></wbr>explanation</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-named-contract%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">flat-<wbr></wbr>named-<wbr></wbr>contract</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">any/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._none%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">none/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">or/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">first-<wbr></wbr>or/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">and/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">not/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3d%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">=/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink"></<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">>/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c~3d%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink"><=/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">>=/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._between%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">between/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._real-in%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">real-<wbr></wbr>in</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">integer-<wbr></wbr>in</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._char-in%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">char-<wbr></wbr>in</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._natural-number%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">natural-<wbr></wbr>number/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._string-len%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">string-<wbr></wbr>len/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._false%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">false/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._printable%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">printable/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._one-of%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">one-<wbr></wbr>of/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._symbols%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">symbols</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vectorof%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">vectorof</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector-immutableof%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">vector-<wbr></wbr>immutableof</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">vector/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector-immutable%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">vector-<wbr></wbr>immutable/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">box/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box-immutable%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">box-<wbr></wbr>immutable/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">listof</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._non-empty-listof%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">non-<wbr></wbr>empty-<wbr></wbr>listof</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Aof%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list*of</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">cons/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fdc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">cons/<span class="mywbr"> </span>dc</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">list/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._%2Alist%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">*list/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._syntax%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">syntax/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">struct/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fdc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">struct/<span class="mywbr"> </span>dc</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._parameter%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">parameter/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._procedure-arity-includes%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">procedure-<wbr></wbr>arity-<wbr></wbr>includes/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">hash/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fdc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">hash/<span class="mywbr"> </span>dc</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._channel%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">channel/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._prompt-tag%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">prompt-<wbr></wbr>tag/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._continuation-mark-key%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">continuation-<wbr></wbr>mark-<wbr></wbr>key/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._evt%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">evt/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-rec-contract%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">flat-<wbr></wbr>rec-<wbr></wbr>contract</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-murec-contract%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">flat-<wbr></wbr>murec-<wbr></wbr>contract</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">any</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._promise%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">promise/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">flat-<wbr></wbr>contract</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-predicate%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">flat-<wbr></wbr>contract-<wbr></wbr>predicate</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._property%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">property/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._suggest%2Fc%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">suggest/<span class="mywbr"> </span>c</span></span></a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="contracts.html" title="backward to "8 Contracts"" data-pltdoc="x">← prev</a> <a href="contracts.html" title="up to "8 Contracts"" data-pltdoc="x">up</a> <a href="function-contracts.html" title="forward to "8.2 Function Contracts"" data-pltdoc="x">next →</a></span> </div><h4 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""data-structure-contracts"">8.1<tt> </tt><a name="(part._data-structure-contracts)"></a>Data-structure Contracts</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._flat-contract-with-explanation))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-with-explanation%29%29" class="RktValDef RktValLink" data-pltdoc="x">flat-contract-with-explanation</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">get-explanation</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktPn">#:name</span><span class="hspace"> </span><span class="RktVar">name</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">get-explanation</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fblame..rkt%29._blame~3f%29%29" class="RktValLink" data-pltdoc="x">blame?</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._object-name%29%29" class="RktValLink" data-pltdoc="x">object-name</a></span><span class="hspace"> </span><span class="RktVar">get-explanation</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Provides a way to use flat contracts that, when a contract fails,
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provide more information about the failure.</div></p><p>If <span class="RktVar">get-explanation</span> returns a boolean, then that boolean value is
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treated as the predicate in a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If it returns
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a procedure, then it is treated similarly to returning <span class="RktVal">#f</span>,
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except the result procedure is called to actually signal the contract
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violation.</p><p>The <span class="RktVar">name</span> argument is used as the name of the contract; it defaults
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to the name of the <span class="RktVar">get-explanation</span> function.</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-with-explanation%29%29" class="RktValLink" data-pltdoc="x">flat-contract-with-explanation</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._cond%29%29" class="RktStxLink" data-pltdoc="x">cond</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._even~3f%29%29" class="RktValLink" data-pltdoc="x">even?</a></span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._else%29%29" class="RktStxLink" data-pltdoc="x">else</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">blame</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">more-information</span><span class="hspace"> </span><span class="RktSym">...do-some-complex-computation-here...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fblame..rkt%29._raise-blame-error%29%29" class="RktValLink" data-pltdoc="x">raise-blame-error</a></span><span class="hspace"> </span><span class="RktSym">blame</span><span class="hspace"> </span><span class="RktSym">val</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">expected:</span><span class="hspace"> </span><span class="RktVal">"an even number"</span><span class="hspace"> </span><span class="RktVal">given:</span><span class="hspace"> </span><span class="RktVal">"~e"</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">"and, here is more help: ~s"</span><span class="RktVal">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">more-information</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._flat-named-contract))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-named-contract%29%29" class="RktValDef RktValLink" data-pltdoc="x">flat-named-contract</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">name</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">flat-contract</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">generator</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat-contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">generator</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">:</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">=</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVal">#f</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Produces a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> like <span class="RktVar">flat-contract</span>, but with the name <span class="RktVar">name</span>.</div></p><p><div class="SIntrapara">For example,
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</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">i</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-named-contract%29%29" class="RktValLink" data-pltdoc="x">flat-named-contract</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">odd-integer</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._odd~3f%29%29" class="RktValLink" data-pltdoc="x">odd?</a></span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p>The generator argument adds a generator for the flat-named-contract. See
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<span class="RktSym"><a href="Random_generation.html#%28def._%28%28lib._racket%2Fcontract..rkt%29._contract-random-generate%29%29" class="RktValLink" data-pltdoc="x">contract-random-generate</a></span> for more information.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/contract/private/misc..rkt)._any/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">any/c</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that accepts any value.</div></p><p>When using this contract as the result portion of a function contract,
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consider using <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span> instead; using <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span> leads to
|
|
better memory performance, but it also allows multiple results.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/contract/private/misc..rkt)._none/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._none%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">none/c</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that accepts no values.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._or/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">or/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Takes any number of <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contracts</span></a> and returns
|
|
a <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> that accepts any value that any one of the contracts
|
|
accepts individually.</div></p><p>The <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span> result tests any value by applying the contracts in
|
|
order, from left to right, with the exception that it always moves the
|
|
non-<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> (if any) to the end, checking them
|
|
last. Thus, a contract such as <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">)</span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._positive~3f%29%29" class="RktValLink" data-pltdoc="x">positive?</a></span><span class="RktPn">)</span> is guaranteed to only invoke the <span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._positive~3f%29%29" class="RktValLink" data-pltdoc="x">positive?</a></span>
|
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predicate on real numbers.</p><p>If all of the arguments are procedures or <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>, the
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|
result is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If only one of the arguments is a
|
|
higher-order contract, the result is a contract that just checks the
|
|
flat contracts and, if they don’t pass, applies the higher-order
|
|
contract.</p><p><div class="SIntrapara">If there are multiple higher-order contracts, <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span> uses
|
|
<span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract-first-order-passes~3f%29%29" class="RktValLink" data-pltdoc="x">contract-first-order-passes?</a></span> to distinguish between
|
|
them. More precisely, when an <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span> is checked, it first
|
|
checks all of the <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>. If none of them pass, it
|
|
calls <span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract-first-order-passes~3f%29%29" class="RktValLink" data-pltdoc="x">contract-first-order-passes?</a></span> with each of the
|
|
higher-order contracts. If only one returns true, <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span> uses
|
|
that contract. If none of them return true, it signals a contract
|
|
violation. If more than one returns true, it also signals a contract
|
|
violation.
|
|
For example, this contract
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|
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">does not accept a function like this one: <span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="stt"> </span><span class="RktSym">args</span><span class="stt"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span>
|
|
since it cannot tell which of the two arrow contracts should be used
|
|
with the function.</div></p><p>If all of its arguments are <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>s, then <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span>
|
|
returns a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._first-or/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">first-or/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Takes any number of <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contracts</span></a> and returns a <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> that
|
|
accepts any value that any one of the contracts accepts
|
|
individually.</div></p><p>The <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span> result tests any value by applying the
|
|
contracts in order from left to right. Thus, a contract
|
|
such as <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">)</span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._positive~3f%29%29" class="RktValLink" data-pltdoc="x">positive?</a></span><span class="RktPn">)</span>
|
|
is guaranteed to only invoke the
|
|
<span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._positive~3f%29%29" class="RktValLink" data-pltdoc="x">positive?</a></span> predicate on real numbers.</p><p>If all of the arguments are procedures or <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat
|
|
contracts</span></a>, the result is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> and
|
|
similarly if all of the arguments are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone
|
|
contracts</span></a> the result is too. Otherwise, the result is an
|
|
<a href="contracts.html#%28tech._impersonator._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator contract</span></a>.</p><p>If there are multiple higher-order contracts,
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span> uses <span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract-first-order-passes~3f%29%29" class="RktValLink" data-pltdoc="x">contract-first-order-passes?</a></span>
|
|
to distinguish between them. More precisely, when an
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span> is checked, it checks the first order passes
|
|
of the first contract against the value. If it succeeds,
|
|
then it uses only that contract. If it fails, then it moves
|
|
to the second contract, continuing until it finds one of
|
|
the contracts where the first order check succeeds. If none
|
|
of them do, a contract violation is signaled.</p><p><div class="SIntrapara">For example, this contract
|
|
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">accepts the function <span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="stt"> </span><span class="RktSym">args</span><span class="stt"> </span><span class="RktVal">0</span><span class="RktPn">)</span>,
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|
applying the <span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="stt"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span> contract to the function
|
|
because it comes first, even though
|
|
<span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="stt"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="stt"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="stt"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span> also applies.</div></p><p>If all of its arguments are <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>s, then <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._first-or%2Fc%29%29" class="RktValLink" data-pltdoc="x">first-or/c</a></span>
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returns a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._and/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">and/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Takes any number of <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contracts</span></a> and returns a <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> that
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accepts any value that satisfies all of the contracts simultaneously.</div></p><p>If all of the arguments are procedures or <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>,
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the result is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>.</p><p>The contract produced by <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span> tests any value by applying
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the contracts in order, from left to right.</p><p>This means that <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span> can be used to guard predicates that are not
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total in contracts. For example, this contract is well-behaved, correctly
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blaming the definition of <span class="RktSym">whoops-not-a-number</span> for not being
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a number:</p><p><div class="SIntrapara"><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">whoops-not-a-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._even~3f%29%29" class="RktValLink" data-pltdoc="x">even?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">"four"</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">whoops-not-a-number: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: real?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: "four"</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: an and/c case of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(and/c real? even?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition whoops-not-a-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition whoops-not-a-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p></div><div class="SIntrapara">but if the arguments to <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span> are reversed, then the contract itself raises
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an error:
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</div><div class="SIntrapara"><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">whoops-not-a-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._even~3f%29%29" class="RktValLink" data-pltdoc="x">even?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">"four"</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">even?: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: integer?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: "four"</span></p></td></tr></table></blockquote></div></p></div></p><p>If more than one of the contracts are not <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>,
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then the order in which the higher-order parts of the contract are tested
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can be counter-intuitive. As an example, consider this function that
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uses <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span> in a higher-order manner with contracts that
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always succeed, but that print when they are called, in order for us
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to see the order in which they are called.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktSym">n</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"show-me ~a\n"</span><span class="hspace"> </span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">identity-with-complex-printing-contract</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">6</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">7</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">show-me</span><span class="hspace"> </span><span class="RktVal">8</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">identity-with-complex-printing-contract</span><span class="hspace"> </span><span class="RktVal">101</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktOut">show-me 1</span></p></td></tr><tr><td><p><span class="RktOut">show-me 2</span></p></td></tr><tr><td><p><span class="RktOut">show-me 3</span></p></td></tr><tr><td><p><span class="RktOut">show-me 4</span></p></td></tr><tr><td><p><span class="RktOut">show-me 5</span></p></td></tr><tr><td><p><span class="RktOut">show-me 6</span></p></td></tr><tr><td><p><span class="RktOut">show-me 7</span></p></td></tr><tr><td><p><span class="RktOut">show-me 8</span></p></td></tr></table></td></tr><tr><td><p><span class="RktRes">101</span></p></td></tr></table></blockquote></div></p><p>The checking order is just like the usual ordering when a contract
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is double-wrapped. The contract that is first put on has its domain checked
|
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second but its range checked first and we see a similar pattern here in
|
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this example, because <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span> simply applies the contracts in order.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._not/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">not/c</a></span></span><span class="hspace"> </span><span class="RktVar">flat-contract</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat-contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Accepts a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> or a predicate and returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>
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that checks the inverse of the argument.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._~3d/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3d%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">=/c</a></span></span><span class="hspace"> </span><span class="RktVar">z</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">z</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the input to be a number and
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<span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span> to <span class="RktVar">z</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._~3c/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x"></c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the input to be a number and
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<span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3c%29%29" class="RktValLink" data-pltdoc="x"><</a></span> than <span class="RktVar">n</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._~3e/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">>/c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c%2Fc%29%29" class="RktValLink" data-pltdoc="x"></c</a></span>, but for <span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3e%29%29" class="RktValLink" data-pltdoc="x">></a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._~3c~3d/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c~3d%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x"><=/c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c%2Fc%29%29" class="RktValLink" data-pltdoc="x"></c</a></span>, but for <span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3c~3d%29%29" class="RktValLink" data-pltdoc="x"><=</a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._~3e~3d/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">>=/c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3c%2Fc%29%29" class="RktValLink" data-pltdoc="x"></c</a></span>, but for <span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3e~3d%29%29" class="RktValLink" data-pltdoc="x">>=</a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._between/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._between%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">between/c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span><span class="RktVar">m</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">m</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara"> Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the
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input to be a real number between <span class="RktVar">n</span> and <span class="RktVar">m</span> or equal to
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one of them.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._real-in))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._real-in%29%29" class="RktValDef RktValLink" data-pltdoc="x">real-in</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span><span class="RktVar">m</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">m</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">An alias for <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._between%2Fc%29%29" class="RktValLink" data-pltdoc="x">between/c</a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._integer-in))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValDef RktValLink" data-pltdoc="x">integer-in</a></span></span><span class="hspace"> </span><span class="RktVar">j</span><span class="hspace"> </span><span class="RktVar">k</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">j</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-integer?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">k</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-integer?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the input to be an exact integer
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between <span class="RktVar">j</span> and <span class="RktVar">k</span>, inclusive. If either <span class="RktVar">j</span> or <span class="RktVar">k</span>
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is <span class="RktVal">#f</span>, then the range is unbounded on that end.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">two-digit-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktVal">99</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">23</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-a-two-digit-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktVal">99</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">124</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-a-two-digit-number: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (integer-in 10 99)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 124</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (integer-in 10 99)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-a-two-digit-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-a-two-digit-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">negative-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-4</span></span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-a-negative-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-a-negative-number: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (integer-in #f -1)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 4</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (integer-in #f -1)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-a-negative-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-a-negative-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:5:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.8.0.2 of package <span class="stt">base</span>: Allow <span class="RktVar">j</span> and <span class="RktVar">k</span> to be <span class="RktVal">#f</span></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._char-in))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._char-in%29%29" class="RktValDef RktValLink" data-pltdoc="x">char-in</a></span></span><span class="hspace"> </span><span class="RktVar">a</span><span class="hspace"> </span><span class="RktVar">b</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">a</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="characters.html#%28def._%28%28quote._~23~25kernel%29._char~3f%29%29" class="RktValLink" data-pltdoc="x">char?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">b</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="characters.html#%28def._%28%28quote._~23~25kernel%29._char~3f%29%29" class="RktValLink" data-pltdoc="x">char?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the input to be a character whose
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code point number is between the code point numbers of <span class="RktVar">a</span> and
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<span class="RktVar">b</span>, inclusive.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/contract/private/misc..rkt)._natural-number/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._natural-number%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">natural-number/c</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that requires the input to be an exact non-negative integer.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._string-len/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._string-len%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">string-len/c</a></span></span><span class="hspace"> </span><span class="RktVar">len</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">len</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that recognizes strings that have fewer than
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<span class="RktVar">len</span> characters.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/contract/private/misc..rkt)._false/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._false%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">false/c</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">An alias for <span class="RktVal">#f</span> for backwards compatibility.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/contract/private/misc..rkt)._printable/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._printable%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">printable/c</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that recognizes values that can be written out and
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read back in with <span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._write%29%29" class="RktValLink" data-pltdoc="x">write</a></span> and <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._one-of/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._one-of%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">one-of/c</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Accepts any number of atomic values and returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that
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recognizes those values, using <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eqv~3f%29%29" class="RktValLink" data-pltdoc="x">eqv?</a></span> as the comparison
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predicate. For the purposes of <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._one-of%2Fc%29%29" class="RktValLink" data-pltdoc="x">one-of/c</a></span>, atomic values are
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defined to be: <a href="characters.html#%28tech._character%29" class="techoutside" data-pltdoc="x"><span class="techinside">characters</span></a>, <a href="symbols.html#%28tech._symbol%29" class="techoutside" data-pltdoc="x"><span class="techinside">symbols</span></a>, <a href="booleans.html#%28tech._boolean%29" class="techoutside" data-pltdoc="x"><span class="techinside">booleans</span></a>,
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<span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._null%29%29" class="RktValLink" data-pltdoc="x">null</a></span>, <a href="keywords.html#%28tech._keyword%29" class="techoutside" data-pltdoc="x"><span class="techinside">keywords</span></a>, <a href="numbers.html#%28tech._number%29" class="techoutside" data-pltdoc="x"><span class="techinside">numbers</span></a>,
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<a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<void></span></span></a>, and <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<undefined></span></span></a>.</div></p><p>This is a backwards compatibility contract constructor. If
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neither <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<void></span></span></a> nor <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<undefined></span></span></a> are arguments,
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it simply passes its arguments to <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._symbols))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._symbols%29%29" class="RktValDef RktValLink" data-pltdoc="x">symbols</a></span></span><span class="hspace"> </span><span class="RktVar">sym</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">sym</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Accepts any number of symbols and returns a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that
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recognizes those symbols.</div></p><p>This is a backwards compatibility constructor; it merely
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passes its arguments to <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/vector..rkt)._vectorof))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vectorof%29%29" class="RktValDef RktValLink" data-pltdoc="x">vectorof</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">c</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVar">immutable</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVar">flat?</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:eager</span><span class="hspace"> </span><span class="RktVar">eager</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">immutable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#t</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">eager</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#t</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#t</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> that recognizes vectors. The elements of the vector must
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match <span class="RktVar">c</span>.</div></p><p>If the <span class="RktVar">flat?</span> argument is <span class="RktVal">#t</span>, then the resulting contract is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>, and the <span class="RktVar">c</span> argument must also be a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. Such
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<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> will be unsound if applied to mutable vectors, as they will not
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check future operations on the vector.</p><p>If the <span class="RktVar">immutable</span> argument is <span class="RktVal">#t</span> and the <span class="RktVar">c</span> argument is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> and the <span class="RktVar">eager</span> argument is <span class="RktVal">#t</span>,
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the result will be a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If the <span class="RktVar">c</span> argument
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is a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>, then the result will be a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>.</p><p>If the <span class="RktVar">eager</span> argument is <span class="RktVal">#t</span>, then immutable vectors are
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checked eagerly when <span class="RktVar">c</span> is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If the
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<span class="RktVar">eager</span> argument is a number <span class="RktSym">n</span>, then immutable vectors are checked
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eagerly when <span class="RktVar">c</span> is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> and the length of the vector
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is less than or equal to <span class="RktSym">n</span>.</p><p>When a higher-order <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vectorof%29%29" class="RktValLink" data-pltdoc="x">vectorof</a></span> contract is applied to a vector, the result
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is not <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input. The result will be a copy for immutable vectors
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and a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the input for mutable vectors,
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unless the <span class="RktVar">c</span> argument is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> and the vector is immutable,
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in which case the result is the original vector.</p><p class="SHistory">Changed in version 6.3.0.5 of package <span class="stt">base</span>: Changed flat vector contracts to not copy
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immutable vectors.<br/>Changed in version 6.7.0.3: Added the <span class="RktPn">#:eager</span> option.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/vector..rkt)._vector-immutableof))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector-immutableof%29%29" class="RktValDef RktValLink" data-pltdoc="x">vector-immutableof</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the same <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> as <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vectorof%29%29" class="RktValLink" data-pltdoc="x">vectorof</a></span><span class="stt"> </span><span class="RktVar">c</span><span class="stt"> </span><span class="RktPn">#:immutable</span><span class="stt"> </span><span class="RktVal">#t</span><span class="RktPn">)</span>. This form exists for
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backwards compatibility.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/vector..rkt)._vector/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">vector/c</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">c</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktMeta">...</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVar">immutable</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVar">flat?</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">immutable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#t</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="contracts.html#%28tech._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract</span></a> that recognizes vectors whose lengths match the number of
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contracts given. Each element of the vector must match its corresponding contract.</div></p><p>If the <span class="RktVar">flat?</span> argument is <span class="RktVal">#t</span>, then the resulting contract is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>, and the <span class="RktVar">c</span> arguments must also be <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>. Such
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<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> will be unsound if applied to mutable vectors, as they will not
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check future operations on the vector.</p><p>If the <span class="RktVar">immutable</span> argument is <span class="RktVal">#t</span> and the <span class="RktVar">c</span> arguments are
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<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>, the result will be a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If the <span class="RktVar">c</span> arguments
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are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>, then the result will be a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>.</p><p>When a higher-order <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector%2Fc%29%29" class="RktValLink" data-pltdoc="x">vector/c</a></span> contract is applied to a vector, the result
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is not <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input. The result will be a copy for immutable vectors
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and a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the input for mutable vectors.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/vector..rkt)._vector-immutable/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector-immutable%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">vector-immutable/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the same contract as <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fvector..rkt%29._vector%2Fc%29%29" class="RktValLink" data-pltdoc="x">vector/c</a></span><span class="stt"> </span><span class="RktVar">c</span><span class="stt"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="stt"> </span><span class="RktPn">#:immutable</span><span class="stt"> </span><span class="RktVal">#t</span><span class="RktPn">)</span>. This form exists for
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reasons of backwards compatibility.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/box..rkt)._box/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">box/c</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">in-c</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">c</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVar">immutable</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVar">flat?</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVar">in-c</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">immutable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#t</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes boxes. The content of the box must match <span class="RktVar">c</span>,
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and mutations on mutable boxes must match <span class="RktVar">in-c</span>.</div></p><p>If the <span class="RktVar">flat?</span> argument is <span class="RktVal">#t</span>, then the resulting contract is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>, and the <span class="RktSym">out</span> argument must also be a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. Such
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<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> will be unsound if applied to mutable boxes, as they will not check
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future operations on the box.</p><p>If the <span class="RktVar">immutable</span> argument is <span class="RktVal">#t</span> and the <span class="RktVar">c</span> argument is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>, the result will be a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. If the <span class="RktVar">c</span> argument is
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a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>, then the result will be a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>.</p><p>When a higher-order <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box%2Fc%29%29" class="RktValLink" data-pltdoc="x">box/c</a></span> contract is applied to a box, the result
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is not <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input. The result will be a copy for immutable boxes
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and either a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the input for mutable boxes.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/box..rkt)._box-immutable/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box-immutable%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">box-immutable/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the same contract as <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fbox..rkt%29._box%2Fc%29%29" class="RktValLink" data-pltdoc="x">box/c</a></span><span class="stt"> </span><span class="RktVar">c</span><span class="stt"> </span><span class="RktPn">#:immutable</span><span class="stt"> </span><span class="RktVal">#t</span><span class="RktPn">)</span>. This form exists for
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reasons of backwards compatibility.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._listof))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValDef RktValLink" data-pltdoc="x">listof</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes a list whose every element matches
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the contract <span class="RktVar">c</span>. Beware that when this contract is applied to
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a value, the result is not necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">some-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">just-one-number</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">11</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">just-one-number: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: list?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 11</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (listof number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition just-one-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition just-one-number)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._non-empty-listof))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._non-empty-listof%29%29" class="RktValDef RktValLink" data-pltdoc="x">non-empty-listof</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes non-empty lists whose elements match
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the contract <span class="RktVar">c</span>. Beware that when this contract is applied to
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a value, the result is not necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">some-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._non-empty-listof%29%29" class="RktValLink" data-pltdoc="x">non-empty-listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-enough-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._non-empty-listof%29%29" class="RktValLink" data-pltdoc="x">non-empty-listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-enough-numbers: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (and/c list? pair?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: '()</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (non-empty-listof number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-enough-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-enough-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._list*of))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Aof%29%29" class="RktValDef RktValLink" data-pltdoc="x">list*of</a></span></span><span class="hspace"> </span><span class="RktVar">ele-c</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">last-c</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">ele-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">last-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVar">ele-c</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes improper lists whose elements match
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the contract <span class="RktVar">ele-c</span> and whose last position matches <span class="RktVar">last-c</span>.
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If an improper list is created with <span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span>,
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then its <span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._car%29%29" class="RktValLink" data-pltdoc="x">car</a></span> position is expected to match <span class="RktVar">ele-c</span> and
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its <span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cdr%29%29" class="RktValLink" data-pltdoc="x">cdr</a></span> position is expected to be <span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Aof%29%29" class="RktValLink" data-pltdoc="x">list*of</a></span><span class="stt"> </span><span class="RktVar">ele-c</span><span class="stt"> </span><span class="RktSym">list-c</span><span class="RktPn">)</span>. Otherwise,
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it is expected to match <span class="RktVar">last-c</span>. Beware that when this contract is applied to
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a value, the result is not necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">improper-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Aof%29%29" class="RktValLink" data-pltdoc="x">list*of</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-improper-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Aof%29%29" class="RktValLink" data-pltdoc="x">list*of</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-improper-numbers: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: number?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: '()</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: an element of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(list*of number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-improper-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-improper-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 6.1.1.1 of package <span class="stt">base</span>.<br/>Changed in version 6.4.0.4: Added the <span class="RktVar">last-c</span> argument.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._cons/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">cons/c</a></span></span><span class="hspace"> </span><span class="RktVar">car-c</span><span class="hspace"> </span><span class="RktVar">cdr-c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">car-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">cdr-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes pairs whose first and second elements
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match <span class="RktVar">car-c</span> and <span class="RktVar">cdr-c</span>, respectively. Beware that
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when this contract is applied to a value, the result is not
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necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</div></p><p>If the <span class="RktVar">cdr-c</span> contract is a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>, then
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<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="RktValLink" data-pltdoc="x">cons/c</a></span> returns a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">a-pair-of-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="RktValLink" data-pltdoc="x">cons/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-a-pair-of-numbers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="RktValLink" data-pltdoc="x">cons/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-a-pair-of-numbers: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: number?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: #f</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the car of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(cons/c number? number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-a-pair-of-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-a-pair-of-numbers)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.0.1.13 of package <span class="stt">base</span>: Added the <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span> propagating behavior.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/base..rkt)._cons/dc))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fdc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">cons/dc</a></span></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">car-id</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">cdr-id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">car-id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktVar">cons/dc-option</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fdc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">cons/dc</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">car-id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">cdr-id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">cdr-id</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktVar">cons/dc-option</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">cons/dc-option</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:flat</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:chaperone</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:impersonator</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes pairs whose first and second elements
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match the expressions after <span class="RktVar">car-id</span> and <span class="RktVar">cdr-id</span>, respectively.</div></p><p>In the first case, the contract on the <span class="RktVar">cdr-id</span> portion of the contract
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may depend on the value in the <span class="RktVar">car-id</span> portion of the pair and in
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the second case, the reverse is true.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">an-ordered-pair-of-reals</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">cons/dc</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">hd</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">tl</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">hd</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="RktValLink" data-pltdoc="x">>=/c</a></span><span class="hspace"> </span><span class="RktSym">hd</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-an-ordered-pair-of-reals</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">cons/dc</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">hd</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">tl</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">hd</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="RktValLink" data-pltdoc="x">>=/c</a></span><span class="hspace"> </span><span class="RktSym">hd</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-an-ordered-pair-of-reals: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (>=/c 2)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 1</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the cdr of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(cons/dc (hd real?) (tl (hd) (>=/c hd)))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-an-ordered-pair-of-reals)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-an-ordered-pair-of-reals)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 6.1.1.6 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._list/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">list/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract for a list. The number of elements in the list
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must match the number of arguments supplied to <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._list%2Fc%29%29" class="RktValLink" data-pltdoc="x">list/c</a></span>, and
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each element of the list must match the corresponding contract. Beware
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that when this contract is applied to a value, the result is not
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necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._*list/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._%2Alist%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">*list/c</a></span></span><span class="hspace"> </span><span class="RktVar">prefix</span><span class="hspace"> </span><span class="RktVar">suffix</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._list-contract~3f%29%29" class="RktValLink" data-pltdoc="x">list-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">prefix</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">suffix</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract for a list. The number of elements in the list
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|
must be at least as long as the number of <span class="RktVar">suffix</span> contracts
|
|
and the tail of the list must match those contracts, one for each
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element. The beginning portion of the list can be arbitrarily long,
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and each element must match <span class="RktVar">prefix</span>.</div></p><p>Beware that when this contract is applied to a value, the result is not
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necessarily <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">a-list-of-numbers-ending-with-two-integers</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._%2Alist%2Fc%29%29" class="RktValLink" data-pltdoc="x">*list/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1/2</span><span class="hspace"> </span><span class="RktVal">4/5</span><span class="hspace"> </span><span class="RktVal">0+1i</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-1</span>1</span><span class="hspace"> </span><span class="RktVal">322</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-enough-integers-at-the-end</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._%2Alist%2Fc%29%29" class="RktValLink" data-pltdoc="x">*list/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">1/2</span><span class="hspace"> </span><span class="RktVal">4/5</span><span class="hspace"> </span><span class="RktVal">1/2</span><span class="hspace"> </span><span class="RktVal">321</span><span class="hspace"> </span><span class="RktVal">322</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">not-enough-integers-at-the-end: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: integer?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 1/2</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the 3rd to the last element of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(*list/c number? integer? integer? integer?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: </span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(definition not-enough-integers-at-the-end)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-enough-integers-at-the-end)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._syntax/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._syntax%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">syntax/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that recognizes syntax objects whose
|
|
<span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax-e%29%29" class="RktValLink" data-pltdoc="x">syntax-e</a></span> content matches <span class="RktVar">c</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/struct-dc..rkt)._struct/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">struct/c</a></span></span><span class="hspace"> </span><span class="RktVar">struct-id</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes instances of the structure
|
|
type named by <span class="RktVar">struct-id</span>, and whose field values match the
|
|
contracts produced by the <span class="RktVar">contract-expr</span>s.</div></p><p>Contracts for immutable fields must be either flat or <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>.
|
|
Contracts for mutable fields may be impersonator contracts.
|
|
If all fields are immutable and the <span class="RktVar">contract-expr</span>s evaluate
|
|
to <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>, a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> is produced. If all the
|
|
<span class="RktVar">contract-expr</span>s are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>, a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a> is
|
|
produced. Otherwise, an impersonator contract is produced.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/struct-dc..rkt)._struct/dc))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fdc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">struct/dc</a></span></span><span class="hspace"> </span><span class="RktVar">struct-id</span><span class="hspace"> </span><span class="RktVar">field-spec</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">maybe-inv</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">field-spec</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">[</span><span class="RktVar">field-name</span><span class="hspace"> </span><span class="RktVar">maybe-lazy</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">[</span><span class="RktVar">field-name</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">dep-field-name</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-lazy</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-contract-type</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-dep-state</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">field-name</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">field-id</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktPn">#:selector</span><span class="hspace"> </span><span class="RktVar">selector-id</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktPn">#:parent</span><span class="hspace"> </span><span class="RktVar">struct-id</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-lazy</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:lazy</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-contract-type</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:flat</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:chaperone</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:impersonator</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-dep-state</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:depends-on-state</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-inv</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:inv</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">dep-field-name</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">invariant-expr</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes instances of the structure
|
|
type named by <span class="RktVar">struct-id</span>, and whose field values match the
|
|
contracts produced by the <span class="RktVar">field-spec</span>s.</div></p><p>If the <span class="RktVar">field-spec</span> lists the names of other fields,
|
|
then the contract depends on values in those fields, and the <span class="RktVar">contract-expr</span>
|
|
expression is evaluated each time a selector is applied, building a new contract
|
|
for the fields based on the values of the <span class="RktVar">dep-field-name</span> fields (the
|
|
<span class="RktVar">dep-field-name</span> syntax is the same as the <span class="RktVar">field-name</span> syntax).
|
|
If the field is a dependent field and no <span class="RktSym">contract-type</span> annotation
|
|
appears, then it is assumed that the contract is
|
|
a chaperone, but not always a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> (and thus the entire <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">struct/dc</a></span>
|
|
contract is not a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>).
|
|
If this is not the case, and the contract is
|
|
always flat then the field must be annotated with
|
|
the <span class="RktPn">#:flat</span>, or the field must be annotated with
|
|
<span class="RktPn">#:impersonator</span> (in which case, it must be a mutable field).</p><p>A <span class="RktVar">field-name</span> is either an identifier naming a field in the first
|
|
case, an identifier naming a selector in the second case indicated
|
|
by the <span class="RktPn">#:selector</span> keyword, or
|
|
a field id for a struct that is a parent of <span class="RktVar">struct-id</span>, indicated
|
|
by the <span class="RktPn">#:parent</span> keyword.</p><p>If the <span class="RktPn">#:lazy</span> keyword appears, then the contract
|
|
on the field is checked lazily (only when a selector is applied);
|
|
<span class="RktPn">#:lazy</span> contracts cannot be put on mutable fields.</p><p>If a dependent contract depends on some mutable state, then use the
|
|
<span class="RktPn">#:depends-on-state</span> keyword argument (if a field’s dependent contract
|
|
depends on a mutable field, this keyword is automatically inferred).
|
|
The presence of this keyword means that the contract expression is evaluated
|
|
each time the corresponding field is accessed (or mutated, if it is a mutable
|
|
field). Otherwise, the contract expression for a dependent field contract
|
|
is evaluated when the contract is applied to a value.</p><p>If the <span class="RktPn">#:inv</span> clause appears, then the invariant expression is
|
|
evaluated (and must return a non-<span class="RktVal">#f</span> value) when the contract
|
|
is applied to a struct.</p><p>Contracts for immutable fields must be either flat or <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>.
|
|
Contracts for mutable fields may be impersonator contracts.
|
|
If all fields are immutable and the <span class="RktVar">contract-expr</span>s evaluate
|
|
to <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>, a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> is produced. If all the
|
|
<span class="RktVar">contract-expr</span>s are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>, a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a> is
|
|
produced. Otherwise, an impersonator contract is produced.</p><p>As an example, the function <span class="RktSym">bst/c</span> below
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|
returns a contract for binary search trees whose values
|
|
are all between <span class="RktSym">lo</span> and <span class="RktSym">hi</span>.
|
|
The lazy annotations ensure that this contract does not
|
|
change the running time of operations that do not
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inspect the entire tree.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">bt</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktSym">right</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bst/c</span><span class="hspace"> </span><span class="RktSym">lo</span><span class="hspace"> </span><span class="RktSym">hi</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">struct/dc</a></span><span class="hspace"> </span><span class="RktSym">bt</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._between%2Fc%29%29" class="RktValLink" data-pltdoc="x">between/c</a></span><span class="hspace"> </span><span class="RktSym">lo</span><span class="hspace"> </span><span class="RktSym">hi</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">left</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:lazy</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bst/c</span><span class="hspace"> </span><span class="RktSym">lo</span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">right</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:lazy</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bst/c</span><span class="hspace"> </span><span class="RktSym">val</span><span class="hspace"> </span><span class="RktSym">hi</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">not-really-a-bst</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bst/c</span><span class="hspace"> </span><span class="RktVal"><span class="nobreak">-i</span>nf.0</span><span class="hspace"> </span><span class="RktVal">+inf.0</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt</span><span class="hspace"> </span><span class="RktVal">5</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt</span><span class="hspace"> </span><span class="RktVal">4</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt</span><span class="hspace"> </span><span class="RktVal">6</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">bt-right</span><span class="hspace"> </span><span class="RktSym">not-really-a-bst</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">bt-val</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt-left</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt-left</span><span class="hspace"> </span><span class="RktSym">not-really-a-bst</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">bt-right</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">bt-left</span><span class="hspace"> </span><span class="RktSym">not-really-a-bst</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">not-really-a-bst: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (between/c 4 5)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 6</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the val field of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">a part of the or/c of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">the right field of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">a part of the or/c of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">the left field of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">a part of the or/c of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(or/c</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">#f</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(struct/dc</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">bt</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(val (between/c -inf.0 +inf.0))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(left (val) #:lazy ...)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(right (val) #:lazy ...)))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition not-really-a-bst)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition not-really-a-bst)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:4:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.0.1.6 of package <span class="stt">base</span>: Added <span class="RktPn">#:inv</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._parameter/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._parameter%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">parameter/c</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">in</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">out</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:impersonator?</span><span class="hspace"> </span><span class="RktVar">impersonator?</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">out</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVar">in</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">impersonator?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#t</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract on parameters whose values must match
|
|
<span class="RktVar">out</span>. When the value in the contracted parameter
|
|
is set, it must match <span class="RktVar">in</span>.</div></p><p>If <span class="RktVar">impersonator?</span> is a true value, then
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._parameter%2Fc%29%29" class="RktValLink" data-pltdoc="x">parameter/c</a></span> always returns an <a href="contracts.html#%28tech._impersonator._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator
|
|
contract</span></a>. If it is <span class="RktVal">#f</span>, then the result will be a
|
|
<a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a> when both <span class="RktVar">in</span> and
|
|
<span class="RktVar">out</span> are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>, and an <a href="contracts.html#%28tech._impersonator._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator contract</span></a> otherwise.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">current-snack</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._parameter%2Fc%29%29" class="RktValLink" data-pltdoc="x">parameter/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="parameters.html#%28def._%28%28quote._~23~25kernel%29._make-parameter%29%29" class="RktValLink" data-pltdoc="x">make-parameter</a></span><span class="hspace"> </span><span class="RktVal">"potato-chip"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">baked/c</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-named-contract%29%29" class="RktValLink" data-pltdoc="x">flat-named-contract</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">baked/c</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">s</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="regexp.html#%28def._%28%28quote._~23~25kernel%29._regexp-match%29%29" class="RktValLink" data-pltdoc="x">regexp-match</a></span><span class="hspace"> </span><span class="RktVal">#rx"baked"</span><span class="hspace"> </span><span class="RktSym">s</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">current-dinner</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._parameter%2Fc%29%29" class="RktValLink" data-pltdoc="x">parameter/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="hspace"> </span><span class="RktSym">baked/c</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="parameters.html#%28def._%28%28quote._~23~25kernel%29._make-parameter%29%29" class="RktValLink" data-pltdoc="x">make-parameter</a></span><span class="hspace"> </span><span class="RktVal">"turkey"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">s</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string-append%29%29" class="RktValLink" data-pltdoc="x">string-append</a></span><span class="hspace"> </span><span class="RktVal">"roasted "</span><span class="hspace"> </span><span class="RktSym">s</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">current-snack</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">not-a-snack</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">current-snack: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: string?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: 'not-a-snack</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the parameter of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(parameter/c string?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition current-snack)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="parameters.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._parameterize%29%29" class="RktStxLink" data-pltdoc="x">parameterize</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">current-dinner</span><span class="hspace"> </span><span class="RktVal">"tofurkey"</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">current-dinner</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">current-dinner: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: baked/c</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: "roasted tofurkey"</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the parameter of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(parameter/c string? baked/c)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition current-dinner)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition current-dinner)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:4:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._procedure-arity-includes/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._procedure-arity-includes%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">procedure-arity-includes/c</a></span></span><span class="hspace"> </span><span class="RktVar">n</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">n</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract for procedures that accept <span class="RktVar">n</span> argument
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(i.e,. the <span class="RktSym"><a href="procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure~3f%29%29" class="RktValLink" data-pltdoc="x">procedure?</a></span> contract is implied).</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/hash..rkt)._hash/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">hash/c</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">key</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">val</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVar">immutable</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVar">flat?</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">key</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">val</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">immutable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#t</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">dont-care</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">flat?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes <span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash%29%29" class="RktValLink" data-pltdoc="x">hash</a></span> tables with keys and values
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as specified by the <span class="RktVar">key</span> and <span class="RktVar">val</span> arguments.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">good-hash</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash%29%29" class="RktValLink" data-pltdoc="x">hash</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">#t</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">bad-hash</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash%29%29" class="RktValLink" data-pltdoc="x">hash</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">"elephant"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">"monkey"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">"manatee"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">bad-hash: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: boolean?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: "elephant"</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the values of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(hash/c integer? boolean?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition bad-hash)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition bad-hash)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara">There are a number of technicalities that control how <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span> contracts
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behave.
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</div><div class="SIntrapara"><ul><li><p>If the <span class="RktVar">flat?</span> argument is <span class="RktVal">#t</span>, then the resulting contract is
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a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>, and the <span class="RktVar">key</span> and <span class="RktVar">val</span> arguments must also be
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<a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">hash/c: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: flat-contract?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: (-> integer? integer?)</span></p></td></tr></table></blockquote></div></p><p>Such <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> will be unsound if applied to mutable hash tables,
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as they will not check future mutations to the hash table.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">original-h</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._make-hasheq%29%29" class="RktValLink" data-pltdoc="x">make-hasheq</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">ctc-h</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span><span class="RktPn">#:flat?</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">original-h</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash-set%21%29%29" class="RktValLink" data-pltdoc="x">hash-set!</a></span><span class="hspace"> </span><span class="RktSym">original-h</span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">"not a boolean"</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash-ref%29%29" class="RktValLink" data-pltdoc="x">hash-ref</a></span><span class="hspace"> </span><span class="RktSym">ctc-h</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"not a boolean"</span></p></td></tr></table></blockquote></div></p></li><li><p>If the <span class="RktVar">immutable</span> argument is <span class="RktVal">#t</span> and the <span class="RktVar">key</span> and
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<span class="RktVar">val</span> arguments are <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span>s, the result will be a
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<span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span>.</p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="hspace"> </span><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></div></p><p>If either the domain or the range is a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span>, then the result will
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be a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></div></p></li><li><p><div class="SIntrapara">If the <span class="RktVar">key</span> argument is a <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span> but not a
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<span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span>, then the resulting contract
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can be applied only to <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span>-based hash tables.
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</div><div class="SIntrapara"><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">h</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._integer~3f%29%29" class="RktValLink" data-pltdoc="x">integer?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._make-hasheq%29%29" class="RktValLink" data-pltdoc="x">make-hasheq</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">h: broke its own contract;</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised equal?-based hash table due to higher-order domain</span></p></td></tr><tr><td><p><span class="RktErr">contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: '#hasheq()</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (hash/c (-> integer? integer?) any/c)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition h)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition h)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p></div><div class="SIntrapara">Also, when such a <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fc%29%29" class="RktValLink" data-pltdoc="x">hash/c</a></span> contract is applied to a hash table, the result is not
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<span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span>
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to the input. The result of applying the contract will be a copy for immutable hash tables,
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and either a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the original hash table
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for mutable hash tables.</div></p></li></ul></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/hash..rkt)._hash/dc))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fdc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">hash/dc</a></span></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">key-id</span><span class="hspace"> </span><span class="RktVar">key-contract-expr</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">value-id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">key-id</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">value-contract-expr</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">hash/dc-option</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">hash/dc-option</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:immutable</span><span class="hspace"> </span><span class="RktVar">immutable?-expr</span><span class="hspace"> </span><span class="RktVar">hash/dc-option</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:kind</span><span class="hspace"> </span><span class="RktVar">kind-expr</span><span class="hspace"> </span><span class="RktVar">hash/dc-option</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Creates a contract for <span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash~3f%29%29" class="RktValLink" data-pltdoc="x">hash?</a></span> tables with keys matching <span class="RktVar">key-contract-expr</span>
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and where the contract on the values can depend on the key itself, since
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<span class="RktVar">key-id</span> will be bound to the corresponding key before evaluating
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the <span class="RktSym">values-contract-expr</span>.</div></p><p>If <span class="RktVar">immutable?-expr</span> is <span class="RktVal">#t</span>, then only <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._immutable~3f%29%29" class="RktValLink" data-pltdoc="x">immutable?</a></span> hashes
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are accepted. If it is <span class="RktVal">#f</span> then <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._immutable~3f%29%29" class="RktValLink" data-pltdoc="x">immutable?</a></span> hashes are always
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rejected. It defaults to <span class="RktVal">'</span><span class="RktVal">dont-care</span>, in which case both mutable and
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immutable hashes are accepted.</p><p>If <span class="RktVar">kind-expr</span> evaluates to <span class="RktVal">'</span><span class="RktVal">flat</span>, then <span class="RktVar">key-contract-expr</span>
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and <span class="RktVar">value-contract-expr</span> are expected to evaluate to <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span>s.
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If it is <span class="RktVal">'</span><span class="RktVal">chaperone</span>, then they are expected to be <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span>s,
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and it may also be <span class="RktVal">'</span><span class="RktVal">impersonator</span>, in which case they may be any <span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span>s.
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The default is <span class="RktVal">'</span><span class="RktVal">chaperone</span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">h</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">hash/dc</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">v</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="RktValLink" data-pltdoc="x">>=/c</a></span><span class="hspace"> </span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash%29%29" class="RktValLink" data-pltdoc="x">hash</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">3</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">h</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fhash..rkt%29._hash%2Fdc%29%29" class="RktStxLink" data-pltdoc="x">hash/dc</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">v</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3e~3d%2Fc%29%29" class="RktValLink" data-pltdoc="x">>=/c</a></span><span class="hspace"> </span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash%29%29" class="RktValLink" data-pltdoc="x">hash</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="hspace"> </span><span class="RktVal">1</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">4</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">h: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: (>=/c 3)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: 1</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the values of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(hash/dc (k real?) (v (k) (>=/c k)))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition h)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition h)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._channel/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._channel%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">channel/c</a></span></span><span class="hspace"> </span><span class="RktVar">val</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">val</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract that recognizes <a href="channel.html#%28tech._channel%29" class="techoutside" data-pltdoc="x"><span class="techinside">channel</span></a>s that communicate
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values as specified by the <span class="RktVar">val</span> argument.</div></p><p>If the <span class="RktVar">val</span> argument is a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>, then the resulting contract
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is a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>. Otherwise, the resulting contract is an impersonator
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contract. When a channel contract is applied to a channel, the resulting channel
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is not <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">chan</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._channel%2Fc%29%29" class="RktValLink" data-pltdoc="x">channel/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="threads.html#%28def._%28%28quote._~23~25kernel%29._thread%29%29" class="RktValLink" data-pltdoc="x">thread</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-get%29%29" class="RktValLink" data-pltdoc="x">channel-get</a></span><span class="hspace"> </span><span class="RktSym">chan</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<thread></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">chan</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">not-a-string</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">chan: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: string?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: 'not-a-string</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (channel/c string?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition chan)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/misc..rkt)._prompt-tag/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._prompt-tag%2Fc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">prompt-tag/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">maybe-call/cc</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-call/cc</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:call/cc</span><span class="hspace"> </span><span class="RktVar">contract</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:call/cc</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="values.html#%28def._%28%28quote._~23~25kernel%29._values%29%29" class="RktValLink" data-pltdoc="x">values</a></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace"> </span></td><td><span class="RktVar">contract</span></td><td><span class="hspace"> </span></td><td>:</td><td><span class="hspace"> </span></td><td><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Takes any number of contracts and returns a contract that recognizes
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continuation prompt tags and will check any aborts or prompt handlers that
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use the contracted prompt tag.</div></p><p>Each <span class="RktVar">contract</span> will check the corresponding value passed to
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an <span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._abort-current-continuation%29%29" class="RktValLink" data-pltdoc="x">abort-current-continuation</a></span> and handled by the handler of a
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call to <span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._call-with-continuation-prompt%29%29" class="RktValLink" data-pltdoc="x">call-with-continuation-prompt</a></span>.</p><p>If all of the <span class="RktVar">contract</span>s are <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>, the resulting
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contract will also be a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> contract. Otherwise, the contract is
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an <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> contract.</p><p>If <span class="RktVar">maybe-call/cc</span> is provided, then the provided contracts
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are used to check the return values from a continuation captured with
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<span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._call-with-current-continuation%29%29" class="RktValLink" data-pltdoc="x">call-with-current-continuation</a></span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym"><a href="creatingunits.html#%28form._%28%28lib._racket%2Funit..rkt%29._tag%29%29" class="RktStxLink" data-pltdoc="x">tag</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._prompt-tag%2Fc%29%29" class="RktStxLink" data-pltdoc="x">prompt-tag/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._make-continuation-prompt-tag%29%29" class="RktValLink" data-pltdoc="x">make-continuation-prompt-tag</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._call-with-continuation-prompt%29%29" class="RktValLink" data-pltdoc="x">call-with-continuation-prompt</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._number-~3estring%29%29" class="RktValLink" data-pltdoc="x">number->string</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._call-with-composable-continuation%29%29" class="RktValLink" data-pltdoc="x">call-with-composable-continuation</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">k</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="cont.html#%28def._%28%28quote._~23~25kernel%29._abort-current-continuation%29%29" class="RktValLink" data-pltdoc="x">abort-current-continuation</a></span><span class="hspace"> </span><span class="RktSym"><a href="creatingunits.html#%28form._%28%28lib._racket%2Funit..rkt%29._tag%29%29" class="RktStxLink" data-pltdoc="x">tag</a></span><span class="hspace"> </span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym"><a href="creatingunits.html#%28form._%28%28lib._racket%2Funit..rkt%29._tag%29%29" class="RktStxLink" data-pltdoc="x">tag</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">k</span><span class="hspace"> </span><span class="RktVal">"not a number"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">tag: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: number?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: "not a number"</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the 1st argument of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(prompt-tag/c</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(-> number? string?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">#:call/cc)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition tag)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._continuation-mark-key/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._continuation-mark-key%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">continuation-mark-key/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Takes a single contract and returns a contract that recognizes
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continuation marks and will check any mappings of marks to values
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or any accesses of the mark value.</div></p><p>If the argument <span class="RktVar">contract</span> is a <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contract</span></a>, the resulting
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contract will also be a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> contract. Otherwise, the contract is
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an <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> contract.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">mark-key</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._continuation-mark-key%2Fc%29%29" class="RktValLink" data-pltdoc="x">continuation-mark-key/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="contmarks.html#%28def._%28%28quote._~23~25kernel%29._make-continuation-mark-key%29%29" class="RktValLink" data-pltdoc="x">make-continuation-mark-key</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="wcm.html#%28form._%28%28quote._~23~25kernel%29._with-continuation-mark%29%29" class="RktStxLink" data-pltdoc="x">with-continuation-mark</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">mark-key</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">s</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._append%29%29" class="RktValLink" data-pltdoc="x">append</a></span><span class="hspace"> </span><span class="RktSym">s</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">truffle</span><span class="hspace"> </span><span class="RktVal">fudge</span><span class="hspace"> </span><span class="RktVal">ganache</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29" class="RktStxLink" data-pltdoc="x">let</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">mark-value</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="contmarks.html#%28def._%28%28quote._~23~25kernel%29._continuation-mark-set-first%29%29" class="RktValLink" data-pltdoc="x">continuation-mark-set-first</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="contmarks.html#%28def._%28%28quote._~23~25kernel%29._current-continuation-marks%29%29" class="RktValLink" data-pltdoc="x">current-continuation-marks</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">mark-key</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">mark-value</span><span class="hspace"> </span><span class="RktVal">"chocolate-bar"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">mark-key: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: symbol?</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: "chocolate-bar"</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the 1st argument of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(continuation-mark-key/c</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(-> symbol? (listof symbol?)))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition mark-key)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._evt/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._evt%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">evt/c</a></span></span><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._chaperone-contract~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone-contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes <a href="sync.html#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable event</span></a>s whose
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<a href="sync.html#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a>s are checked by the given
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<span class="RktVar">contract</span>s.</div></p><p>The resulting contract is always a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> contract and its
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arguments must all be <a href="contracts.html#%28tech._chaperone._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone contracts</span></a>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">my-evt</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._evt%2Fc%29%29" class="RktValLink" data-pltdoc="x">evt/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._always-evt%29%29" class="RktValLink" data-pltdoc="x">always-evt</a></span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">failing-evt</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._evt%2Fc%29%29" class="RktValLink" data-pltdoc="x">evt/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._alarm-evt%29%29" class="RktValLink" data-pltdoc="x">alarm-evt</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="time.html#%28def._%28%28quote._~23~25kernel%29._current-inexact-milliseconds%29%29" class="RktValLink" data-pltdoc="x">current-inexact-milliseconds</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">50</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym">my-evt</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<always-evt></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym">failing-evt</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">failing-evt: broke its own contract</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">promised: event that produces 2 values</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">produced: event that produces 1 values</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (evt/c number? number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (definition failing-evt)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: (definition failing-evt)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/base..rkt)._flat-rec-contract))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-rec-contract%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">flat-rec-contract</a></span></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">flat-contract-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a recursive <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>. A
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<span class="RktVar">flat-contract-expr</span> can refer to <span class="RktVar">id</span> to refer
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recursively to the generated contract.</div></p><p>For example, the contract</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-rec-contract%29%29" class="RktStxLink" data-pltdoc="x">flat-rec-contract</a></span><span class="hspace"> </span><span class="RktSym">sexp</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._cons%2Fc%29%29" class="RktValLink" data-pltdoc="x">cons/c</a></span><span class="hspace"> </span><span class="RktSym">sexp</span><span class="hspace"> </span><span class="RktSym">sexp</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="RktPn">)</span></td></tr></table></blockquote><p>is a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that checks for (a limited form of)
|
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S-expressions. It says that a <span class="RktVar">sexp</span> is either two
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|
<span class="RktVar">sexp</span>s combined with <span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span>, or a number, or a symbol.</p><p>Note that if the contract is applied to a circular value, contract
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checking will not terminate.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/base..rkt)._flat-murec-contract))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-murec-contract%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">flat-murec-contract</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">flat-contract-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span><span class="RktMeta">...+</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A generalization of <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-rec-contract%29%29" class="RktStxLink" data-pltdoc="x">flat-rec-contract</a></span> for defining several
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|
mutually recursive <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> simultaneously. Each <span class="RktVar">id</span> is
|
|
visible in the entire <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._flat-murec-contract%29%29" class="RktStxLink" data-pltdoc="x">flat-murec-contract</a></span> form, and the
|
|
result of the final <span class="RktVar">body</span> is the result of the entire form.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><a name="(form._((lib._racket/contract/private/misc..rkt)._any))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">any</a></span></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Represents a contract that is always satisfied. In particular, it can accept
|
|
multiple values. It can only be used in a result position of contracts like
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|
<span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span>. Using <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span> elsewhere is a syntax error.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._promise/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._promise%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">promise/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a contract on a promise. The contract does not force the
|
|
promise, but when the promise is forced, the contract checks that the
|
|
result value meets the contract <span class="RktVar">c</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._flat-contract))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract%29%29" class="RktValDef RktValLink" data-pltdoc="x">flat-contract</a></span></span><span class="hspace"> </span><span class="RktVar">predicate</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">predicate</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> from <span class="RktVar">predicate</span>. A value
|
|
satisfies the contract if the predicate returns a true value.</div></p><p>This function is a holdover from before predicates could be used
|
|
directly as <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a>. It exists today for backwards compatibility.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._flat-contract-predicate))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-predicate%29%29" class="RktValDef RktValLink" data-pltdoc="x">flat-contract-predicate</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Extracts the predicate from a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a>.</div></p><p>Note that most <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contracts</span></a> can be used directly as predicates, but not all.
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|
This function can be used to build predicates for ordinary Racket values that double
|
|
as contracts, such as numbers and symbols. When building a <a href="contracts.html#%28tech._contract._combinator%29" class="techoutside" data-pltdoc="x"><span class="techinside">contract combinator</span></a>
|
|
that needs to explicitly convert ordinary racket values to flat contracts, consider
|
|
using <span class="RktSym"><a href="Building_New_Contract_Combinators.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._coerce-flat-contract%29%29" class="RktValLink" data-pltdoc="x">coerce-flat-contract</a></span> instead of <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._flat-contract-predicate%29%29" class="RktValLink" data-pltdoc="x">flat-contract-predicate</a></span> so
|
|
that the combinator can raise errors that use the combinator’s name in the error
|
|
message.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/base..rkt)._property/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._property%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">property/c</a></span></span><span class="hspace"> </span><span class="RktVar">accessor</span><span class="hspace"> </span><span class="RktVar">ctc</span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktPn">#:name</span><span class="hspace"> </span><span class="RktVar">name</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">accessor</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">ctc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">name</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._object-name%29%29" class="RktValLink" data-pltdoc="x">object-name</a></span><span class="hspace"> </span><span class="RktVar">accessor</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a <a href="contracts.html#%28tech._flat._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">flat contract</span></a> that checks that the first-order property
|
|
accessed by <span class="RktVar">accessor</span> satisfies <span class="RktVar">ctc</span>. The resulting contract
|
|
is equivalent to</div></p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">ctc</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">accessor</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote><p>except that more information is included in error messages produced by
|
|
violations of the contract. The <span class="RktVar">name</span> argument is used to describe the
|
|
property being checked in error messages.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">sum-triple</span><span class="hspace"> </span><span class="RktSym">lst</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._property%2Fc%29%29" class="RktValLink" data-pltdoc="x">property/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._length%29%29" class="RktValLink" data-pltdoc="x">length</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._~3d%2Fc%29%29" class="RktValLink" data-pltdoc="x">=/c</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._number~3f%29%29" class="RktValLink" data-pltdoc="x">number?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._first%29%29" class="RktValLink" data-pltdoc="x">first</a></span><span class="hspace"> </span><span class="RktSym">lst</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._second%29%29" class="RktValLink" data-pltdoc="x">second</a></span><span class="hspace"> </span><span class="RktSym">lst</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._third%29%29" class="RktValLink" data-pltdoc="x">third</a></span><span class="hspace"> </span><span class="RktSym">lst</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sum-triple</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">6</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">sum-triple</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">sum-triple: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">expected: (=/c 3)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">given: 2</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: the length of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">an and/c case of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">the 1st argument of</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(-></span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(and/c</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(listof number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(property/c length (=/c 3)))</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">number?)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (function sum-triple)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:2:0</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 7.3.0.11 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/private/misc..rkt)._suggest/c))"></a><span title="Provided from: racket/contract/base, racket/contract, racket | Package: base"><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._suggest%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">suggest/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span><span class="RktVar">field</span><span class="hspace"> </span><span class="RktVar">message</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">field</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">message</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that behaves like <span class="RktVar">c</span>, except
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that it adds an extra line to the error message on a contract
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violation.</div></p><p>The <span class="RktVar">field</span> and <span class="RktVar">message</span> strings are added
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following the guidelines in
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<a href="exns.html#%28part._err-msg-conventions%29" data-pltdoc="x">Error Message Conventions</a>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">allow-calls?</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._suggest%2Fc%29%29" class="RktValLink" data-pltdoc="x">suggest/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%2A%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>*</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:pre</span><span class="hspace"> </span><span class="RktSym">allow-calls?</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">"suggestion"</span><span class="hspace"> </span><span class="RktVal">"maybe you should set! allow-calls? to #t"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">f</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">f: contract violation</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">#:pre condition</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">suggestion: maybe you should set! allow-calls? to #t</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">in: (->* () #:pre ... any)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">contract from: (function f)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">blaming: top-level</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">(assuming the contract is correct)</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace"> </span><span class="RktErr">at: eval:3:0</span></p></td></tr></table></blockquote></div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="contracts.html" title="backward to "8 Contracts"" data-pltdoc="x">← prev</a> <a href="contracts.html" title="up to "8 Contracts"" data-pltdoc="x">up</a> <a href="function-contracts.html" title="forward to "8.2 Function Contracts"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |