28 lines
No EOL
18 KiB
HTML
28 lines
No EOL
18 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<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>8.4 Lazy 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="tocviewlink" 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="tocviewselflink" 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="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._contract-struct%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">contract-<wbr></wbr>struct</span></span></a></td></tr><tr><td><a href="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._define-contract-struct%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>contract-<wbr></wbr>struct</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="parametric-contracts.html" title="backward to "8.3 Parametric Contracts"" data-pltdoc="x">← prev</a> <a href="contracts.html" title="up to "8 Contracts"" data-pltdoc="x">up</a> <a href="Structure_Type_Property_Contracts.html" title="forward to "8.5 Structure Type Property 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=""Lazy_Data-structure_Contracts"">8.4<tt> </tt><a name="(part._.Lazy_.Data-structure_.Contracts)"></a>Lazy 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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/ds..rkt)._contract-struct))"></a><span title="Provided from: racket/contract, racket | Package: base"><span class="RktSym"><a href="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._contract-struct%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">contract-struct</a></span></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote><p><span style="background-color: yellow"><span style="font-weight: bold">NOTE:</span></span> This library is deprecated; use <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>, instead. Lazy struct contracts no longer require a separate
|
|
struct declaration; instead <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>
|
|
and <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fc%29%29" class="RktStxLink" data-pltdoc="x">struct/c</a></span> work directly with
|
|
<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> and <span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>.</p></blockquote></div></p><p>Like <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>, but with two differences:
|
|
they do not
|
|
define field mutators, and they define two contract constructors:
|
|
<span class="RktVar">id</span><span class="RktSym">/c</span> and <span class="RktVar">id</span><span class="RktSym">/dc</span>. The
|
|
first is a procedure that accepts as many arguments as there are
|
|
fields and returns a contract for struct values whose fields match the
|
|
arguments. The second is a syntactic form that also produces contracts
|
|
on the structs, but the contracts on later fields may depend on the
|
|
values of earlier fields.</p><p>The generated contract combinators are <span style="font-style: italic">lazy</span>: they only verify
|
|
the contract holds for the portion of some data structure that is
|
|
actually inspected. More precisely, a lazy data structure contract is
|
|
not checked until a selector extracts a field of a struct.</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktPn">(</span><span class="RktVar">id</span><span class="RktSym">/dc</span><span class="hspace"> </span><span class="RktVar">field-spec</span><span class="hspace"> </span><span class="RktMeta">...</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">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-id</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"><span class="RktPn">[</span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">]</span></td></tr></table></td></tr></table></blockquote><p>In each <span class="RktVar">field-spec</span> case, the first <span class="RktVar">field-id</span>
|
|
specifies which field the contract applies to; the fields must be
|
|
specified in the same order as the original
|
|
<span class="RktSym"><a href="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._contract-struct%29%29" class="RktStxLink" data-pltdoc="x">contract-struct</a></span>. The first case is for when the
|
|
contract on the field does not depend on the value of any other
|
|
field. The second case is for when the contract on the field does
|
|
depend on some other fields, and the parenthesized <span class="RktVar">field-id</span>s
|
|
indicate which fields it depends on; these dependencies can only be to
|
|
earlier fields.</p></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/contract/private/ds..rkt)._define-contract-struct))"></a><span title="Provided from: racket/contract, racket | Package: base"><span class="RktSym"><a href="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._define-contract-struct%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-contract-struct</a></span></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"><blockquote><p><span style="background-color: yellow"><span style="font-weight: bold">NOTE:</span></span> This library is deprecated; use <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>, instead. Lazy struct contracts no longer require a separate
|
|
struct declaration; instead <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>
|
|
and <span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fstruct-dc..rkt%29._struct%2Fc%29%29" class="RktStxLink" data-pltdoc="x">struct/c</a></span> work directly with
|
|
<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> and <span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>.</p></blockquote></div></p><p>Like <span class="RktSym"><a href="Lazy_Data-structure_Contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fds..rkt%29._contract-struct%29%29" class="RktStxLink" data-pltdoc="x">contract-struct</a></span>, but where the constructor’s name is
|
|
<span class="RktSym">make-</span><span class="RktVar">id</span>, much like <span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span>.</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="parametric-contracts.html" title="backward to "8.3 Parametric Contracts"" data-pltdoc="x">← prev</a> <a href="contracts.html" title="up to "8 Contracts"" data-pltdoc="x">up</a> <a href="Structure_Type_Property_Contracts.html" title="forward to "8.5 Structure Type Property Contracts"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |