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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>8.10 Collapsible 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" cl
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to avoid a particular pathological build up of contract wrappers on higher-order
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values. The <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="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>, and <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> contract
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combinators support collapsing for vector contracts and function contracts for
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functions returning a single value.</p><p>Intuitively, a collapsible contract is a tree structure.
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The <a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-ho%2Fc%29%29" data-pltdoc="x">tree nodes</a> represent higher-order contracts
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(e.g., <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>) and the <a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-leaf%2Fc%29%29" data-pltdoc="x">tree leaves</a>
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represent sequences of flat contracts.
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Two trees can collapse into one tree via the <span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._merge%29%29" class="RktValLink" data-pltdoc="x">merge</a></span> procedure,
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which removes unnecessary flat contracts from the leaves.</p><p>For more information on the motivation and design of collapsible contracts,
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see [<a href="doc-bibliography.html#%28cite._.Feltey18%29" data-pltdoc="x">Feltey18</a>].
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For the theoretical foundations, see [<a href="doc-bibliography.html#%28cite._.Greenberg15%29" data-pltdoc="x">Greenberg15</a>].</p><p><span style="font-weight: bold">Warning</span>: the features described in this section are experimental
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and may not be sufficient to implement new collapsible contracts. Implementing
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new collapsible contracts requires the use of unsafe chaperones and impersonators
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which are only supported for vector and procedure values. This documentation exists
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primarily to allow future maintenance of the <span class="RktSym">racket/contract/collapsible</span>
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library. <span style="font-weight: bold">End Warning</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/guts..rkt)._get/build-collapsible-late-neg-projection))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._get%2Fbuild-collapsible-late-neg-projection%29%29" class="RktValDef RktValLink" data-pltdoc="x">get/build-collapsible-late-neg-projection</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span></p></blockquote></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="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="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="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="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="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span><span class="RktPn">)</span><span class="RktPn">)</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></td></tr></table></blockquote></div><div class="SIntrapara">Returns the <span class="RktVar">collapsible-late-neg</span> projection for <span class="RktVar">c</span>.</div></p><p>If <span class="RktVar">c</span> does not have a <span class="RktVar">collapsible-late-neg</span> projection,
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then this function uses the original projection for it and constructs a leaf
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as its collapsible representation.</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/guts..rkt)._collapsible-contract-continuation-mark-key))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._collapsible-contract-continuation-mark-key%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-contract-continuation-mark-key</a></span></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contmarks.html#%28def._%28%28quote._~23~25kernel%29._continuation-mark-key~3f%29%29" class="RktValLink" data-pltdoc="x">continuation-mark-key?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Key used by continuation marks that are present during collapsible contract checking.
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The value of these marks are <span class="RktVal">#t</span> if the current contract is collapsible.</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/guts..rkt)._with-collapsible-contract-continuation-mark))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._with-collapsible-contract-continuation-mark%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">with-collapsible-contract-continuation-mark</a></span></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">Inserts a continuation mark that informs the contract profiler that the current contract
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is collapsible.</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/collapsible..rkt)._prop~3acollapsible-contract))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._prop~3acollapsible-contract%29%29" class="RktValDef RktValLink" data-pltdoc="x">prop:collapsible-contract</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="structprops.html#%28def._%28%28quote._~23~25kernel%29._struct-type-property~3f%29%29" class="RktValLink" data-pltdoc="x">struct-type-property?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Structures implementing this property are usable as collapsible contracts. The value
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associated with this property should be constructed by calling
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<span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._build-collapsible-contract-property%29%29" class="RktValLink" data-pltdoc="x">build-collapsible-contract-property</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/collapsible..rkt)._collapsible-contract~3f))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-contract?</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="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</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">A predicate recognizing structures with the <span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._prop~3acollapsible-contract%29%29" class="RktValLink" data-pltdoc="x">prop:collapsible-contract</a></span> property.</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/collapsible..rkt)._merge))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._merge%29%29" class="RktValDef RktValLink" data-pltdoc="x">merge</a></span></span><span class="hspace"> </span><span class="RktVar">new-cc</span><span class="hspace"> </span><span class="RktVar">new-neg</span><span class="hspace"> </span><span class="RktVar">old-cc</span><span class="hspace"> </span><span class="RktVar">old-neg</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">new-cc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">new-neg</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">old-cc</span><span class="hspace"> </span>:<span clas
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The <span class="RktVar">new-neg</span> and <span class="RktVar">old-neg</span> arguments are expected to be
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blame parties similar to those passed to a <a href="Building_New_Contract_Combinators.html#%28tech._late._neg._projection%29" class="techoutside" data-pltdoc="x"><span class="techinside">late neg projection</span></a>.</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/collapsible..rkt)._collapsible-guard))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-guard%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-guard</a></span></span><span class="hspace"> </span><span class="RktVar">cc</span><span class="hspace"> </span><span class="RktVar">val</span><span class="hspace"> </span><span class="RktVar">neg-party</span><span class="RktPn">)</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></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">cc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-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="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">neg-party</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">Similar to a <a href="Building_New_Contract_Combinators.html#%28tech._late._neg._projection%29" class="techoutside" data-pltdoc="x"><span class="techinside">late neg projection</span></a>, this function guards the value <span class="RktVar">val</span>
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with the collapsible contract <span class="RktVar">cc</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/collapsible..rkt)._collapsible-contract-property~3f))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract-property~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-contract-property?</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="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</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">This predicate indicates that a value can be used as the property for
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<span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._prop~3acollapsible-contract%29%29" class="RktValLink" data-pltdoc="x">prop:collapsible-contract</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><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top" colspan="3"><span class="RktPn">(</span><a name="(def._((lib._racket/contract/collapsible..rkt)._build-collapsible-contract-property))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._build-collapsible-contract-property%29%29" class="RktValDef RktValLink" data-pltdoc="x">build-collapsible-contract-property</a></span></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">#:try-merge</span><span class="hspace"> </span><span class="RktVar">try-merge</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">#:collapsible-guard</span><span class="hspace"> </span><span class="RktVar">collapsible-guard</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="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract-property~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract-property?</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">try-merge</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"><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="RktVal">#f</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="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span></td></tr><tr><td><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="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span></td></tr><tr><td><span class="hspace"> &n
|
||
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The <span class="RktVar">try-merge</span> argument is similar to <span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._merge%29%29" class="RktValLink" data-pltdoc="x">merge</a></span>, but may return <span class="RktVal">#f</span> instead
|
||
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of a collapsible contract and may be specialized to a particular collapsible contract.
|
||
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|
The <span class="RktVar">collapsible-guard</span> argument should be specialized to the particular collapsible
|
||
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|
contract being implemented.</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>struct</p></div></div><p class="RForeground"><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="stt"> </span><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-ho/c-latest-ctc))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-ho/c-missing-party))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-ho/c-latest-blame))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-ho/c~3f))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._struct~3acollapsible-ho/c))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-ho/c))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-ho%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-ho/c</a></span></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">latest-blame</span><span class="stt"> </span><span class="RktSym">missing-party</span><span class="stt"> </span><span class="RktSym">latest-ctc</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">latest-blame</span><span class="hspace"> </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></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">missing-party</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="RktSym">latest-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._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A common parent structure for collapsible contracts for higher-order values.
|
||
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The <span class="RktSym">latest-blame</span> field holds the blame object for the most recent
|
||
|
|
contract attached. Similarly, the <span class="RktSym">missing-party</span> field holds the latest
|
||
|
|
missing party passed to the contract. The <span class="RktSym">latest-contract</span> field stores
|
||
|
|
the most recent contract attached to the value.</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>struct</p></div></div><table cellspacing="0" cellpadding="0" class="RForeground"><tr><td><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></td><td><span class="hspace"> </span></td><td><span class="nobreak"><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c-missing-party-list))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c-blame-list))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c-contract-list))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c-proj-list))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c~3f))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._struct~3acollapsible-leaf/c))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-leaf/c))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-leaf%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-leaf/c</a></span></span></span></td><td><span class="hspace"> </span><span class="RktPn">(</span></td><td><span class="nobreak"><span class="RktSym">proj-list</span></span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktSym">contract-list</span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktSym">blame-list</span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktSym">missing-party-list</span><span class="RktPn">))</span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">proj-list</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._listof%29%29" class="RktValLink" data-pltdoc="x">listof</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="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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">contract-list</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a
|
||
|
|
field holds a list of partially applied <a href="Building_New_Contract_Combinators.html#%28tech._late._neg._projection%29" class="techoutside" data-pltdoc="x"><span class="techinside">late neg projections</span></a>. The <span class="RktSym">contract-list</span>,
|
||
|
|
<span class="RktSym">blame-list</span>, and <span class="RktSym">missing-party-list</span> fields hold a list of contracts,
|
||
|
|
blame objects, and blame missing parties respectively.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><table cellspacing="0" cellpadding="0" class="together"><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/collapsible..rkt)._impersonator-prop~3acollapsible))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._impersonator-prop~3acollapsible%29%29" class="RktValDef RktValLink" data-pltdoc="x">impersonator-prop:collapsible</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator-property~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator-property?</a></span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><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/collapsible..rkt)._has-impersonator-prop~3acollapsible~3f))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._has-impersonator-prop~3acollapsible~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">has-impersonator-prop:collapsible?</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="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</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></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="together"><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/collapsible..rkt)._get-impersonator-prop~3acollapsible))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._get-impersonator-prop~3acollapsible%29%29" class="RktValDef RktValLink" data-pltdoc="x">get-impersonator-prop:collapsible</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="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-property~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-property?</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></td></tr></table></blockquote></div><div class="SIntrapara">An impersonator property (and its acc
|
||
|
|
values that are guarded with a collapsible contract.</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>struct</p></div></div><p class="RForeground"><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="stt"> </span><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-property-ref))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-property-neg-party))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-property-c-c))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-property~3f))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._struct~3acollapsible-property))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-property))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-property%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-property</a></span></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym">c-c</span><span class="stt"> </span><span class="RktSym">neg-party</span><span class="stt"> </span><span class="RktSym">ref</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">c-c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-contract~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-contract?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">neg-party</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="RktSym">ref</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">#f</span><span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">The parent struct of properties that should be attached to chaperones or impersonators
|
||
|
|
of values protected with a collapsible contract. The <span class="RktSym">c-c</span> field stores the collapsible
|
||
|
|
contract that is or will in the future be attached to the the value. The <span class="RktSym">neg-party</span> field
|
||
|
|
stores the latest missing blame party passed to the contract on the value. The <span class="RktSym">ref</span> field
|
||
|
|
is mutable and stores a reference to the chaperone or impersonator to which this property is
|
||
|
|
attached. This is necessary to determine whether an unknown chaperone has been attached to a value
|
||
|
|
after it has been protected by a collapsible contract.
|
||
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</div><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>struct</p></div></div><table cellspacing="0" cellpadding="0" class="RForeground"><tr><td><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></td><td><span class="hspace"> </span></td><td><span class="nobreak"><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-count-property-prev))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-count-property-count))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-count-property~3f))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._struct~3acollapsible-count-property))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-count-property))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-count-property%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-count-property</a></span></span><span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-property%29%29" class="RktValLink" data-pltdoc="x">collapsible-property</a></span></span></td><td><span class="hspace"> </span><span class="RktPn">(</span></td><td><span class="nobreak"><span class="RktSym">count</span></span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktSym">prev</span><span class="RktPn">))</span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">count</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._natural-number%2Fc%29%29" class="RktValLink" data-pltdoc="x">natural-number/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">prev</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="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-count-property~3f%29%29" class="RktValLink" data-pltdoc="x">collapsible-count-property?</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">This property is associated with the <span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._impersonator-prop~3acollapsible%29%29" class="RktValLink" data-pltdoc="x">impersonator-prop:collapsible</a></span> property before
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the value completely enters the collapsible mode. These properties keep track of the number of
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contracts on a value in the <span class="RktVar">count</span> field, and hold a reference to the previous
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<a name="(tech._count._property)"></a><span style="font-style: italic">count property</span> in the <span class="RktSym">prev</span> field or the original value without a contract. This
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allows the contract system to traverse the chain of attached contracts and merge them into a single
|
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collapsible contract to protect the original value.
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</div><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>struct</p></div></div><table cellspacing="0" cellpadding="0" class="RForeground"><tr><td><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></td><td><span class="hspace"> </span></td><td><span class="nobreak"><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-wrapper-property-checking-wrapper))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-wrapper-property~3f))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._struct~3acollapsible-wrapper-property))"></a><a name="(def._((lib._racket/contract/collapsible..rkt)._collapsible-wrapper-property))"></a><span title="Provided from: racket/contract/collapsible, racket/contract, racket | Package: base"><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-wrapper-property%29%29" class="RktValDef RktValLink" data-pltdoc="x">collapsible-wrapper-property</a></span></span><span class="hspace"> </span><span class="RktSym"><a href="collapsible.html#%28def._%28%28lib._racket%2Fcontract%2Fcollapsible..rkt%29._collapsible-property%29%29" class="RktValLink" data-pltdoc="x">collapsible-property</a></span></span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktPn">(</span><span class="nobreak"><span class="RktSym">checking-wrapper</span><span class="RktPn">)</span></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">checking-wrapper</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">This property is used when a value is guarded by a collapsible contract. The
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<span class="RktSym">checking-wrapper</span> field holds a chaperone or impersonator that dispatches to the
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collapsible contract stored in this property to perform any necessary contract checks. When
|
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the value receives another contract and merging happens, the checking wrapper will remain the
|
||
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same even though the specific collapsible contract attached to the value may change.</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="racket_contract_base.html" title="backward to "8.9 racket/contract/base"" data-pltdoc="x">← prev</a> <a href="contracts.html" title="up to "8 Contracts"" data-pltdoc="x">up</a> <a href="Legacy_Contracts.html" title="forward to "8.11 Legacy Contracts"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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