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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>3.18&nbsp;Iterations and Comprehensions: for, for/list, ...</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="icons.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,&quot;tocview_0&quot;);">&#9658;</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&nbsp;</td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2&nbsp;</td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3&nbsp;</td><td><a href="syntax.html" class="tocviewselflink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4&nbsp;</td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5&nbsp;</td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6&nbsp;</td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7&nbsp;</td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8&nbsp;</td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9&nbsp;</td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10&nbsp;</td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11&nbsp;</td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12&nbsp;</td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13&nbsp;</td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14&nbsp;</td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15&nbsp;</td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16&nbsp;</td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17&nbsp;</td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18&nbsp;</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,&quot;tocview_1&quot;);">&#9660;</a></td><td>3&nbsp;</td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr></table><div class="tocviewsublist" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">3.1&nbsp;</td><td><a href="module.html" class="tocviewlink" data-pltdoc="x">Modules:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">module</span></span>, <span class="RktSym"><span class="RktStxLink">module*</span></span>, ...</a></td></tr><tr><td align="right">3.2&nbsp;</td><td><a href="require.html" class="tocviewlink" data-pltdoc="x">Importing and Exporting:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">require</span></span> and <span class="RktSym"><span class="RktStxLink">provide</span></span></a></td></tr><tr><td align="right">3.3&nbsp;</td><td><a href="quote.html" class="tocviewlink" data-pltdoc="x">Literals:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">quote</span></span> and <span class="RktSym"><span class="RktStxLink">#%datum</span></span></a></td></tr><tr><td align="right">3.4&nbsp;</td><td><a href="__expression.html" class="tocviewlink" data-pltdoc="x">Expression Wrapper:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">#%expression</span></span></a></td></tr><tr><td align="right">3.5&nbsp;</td><td><a href="__top.html" class="tocviewlink" data-pltdoc="x">Variable References and <span class="RktSym"><span class="RktStxLink">#%top</span></span></a></td></tr><tr><td align="right">3.6&nbsp;</td><td><a href="Locations____variable-reference.html" class="tocviewlink" data-pltdoc="x">Locations:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">#%variable-<wbr></wbr>reference</span></span></a></td></tr><tr><td align="right">3.7&nbsp;</td><td><a href="application.html" class="tocviewlink" data-pltdoc="x">Procedure Applications and <span class="RktSym"><span class="RktStxLink">#%app</span></span></a></td></tr><tr><td align="right">3.8&nbsp;</td><td><a href="lambda.html" class="tocviewlink" data-pltdoc="x">Procedure Expressions:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">lambda</span></span> and <span class="RktSym"><span class="RktStxLink">case-<wbr></wbr>lambda</span></span></a></td></tr><tr><td align="right">3.9&nbsp;</td><td><a href="let.html" class="tocviewlink" data-pltdoc="x">Local Binding:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">let</span></span>, <span class="RktSym"><span class="RktStxLink">let*</span></span>, <span class="RktSym"><span class="RktStxLink">letrec</span></span>, ...</a></td></tr><tr><td align="right">3.10&nbsp;</td><td><a href="local.html" class="tocviewlink" data-pltdoc="x">Local Definitions:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">local</span></span></a></td></tr><tr><td align="right">3.11&nbsp;</td><td><a href="shared.html" class="tocviewlink" data-pltdoc="x">Constructing Graphs:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">shared</span></span></a></td></tr><tr><td align="right">3.12&nbsp;</td><td><a href="if.html" class="tocviewlink" data-pltdoc="x">Conditionals:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">if</span></span>, <span class="RktSym"><span class="RktStxLink">cond</span></span>, <span class="RktSym"><span class="RktStxLink">and</span></span>, and <span class="RktSym"><span class="RktStxLink">or</span></span></a></td></tr><tr><td align="right">3.13&nbsp;</td><td><a href="case.html" class="tocviewlink" data-pltdoc="x">Dispatch:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">case</span></span></a></td></tr><tr><td align="right">3.14&nbsp;</td><td><a href="define.html" class="tocviewlink" data-pltdoc="x">Definitions:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">define</span></span>, <span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>syntax</span></span>, ...</a></td></tr><tr><td align="right">3.15&nbsp;</td><td><a href="begin.html" class="tocviewlink" data-pltdoc="x">Sequencing:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">begin</span></span>, <span class="RktSym"><span class="RktStxLink">begin0</span></span>, and <span class="RktSym"><span class="RktStxLink">begin-<wbr></wbr>for-<wbr></wbr>syntax</span></span></a></td></tr><tr><td align="right">3.16&nbsp;</td><td><a href="when_unless.html" class="tocviewlink" data-pltdoc="x">Guarded Evaluation:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">when</span></span> and <span class="RktSym"><span class="RktStxLink">unless</span></span></a></td></tr><tr><td align="right">3.17&nbsp;</td><td><a href="set_.html" class="tocviewlink" data-pltdoc="x">Assignment:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">set!</span></span> and <span class="RktSym"><span class="RktStxLink">set!-<wbr></wbr>values</span></span></a></td></tr><tr><td align="right">3.18&nbsp;</td><td><a href="for.html" class="tocviewselflink" data-pltdoc="x">Iterations and Comprehensions:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">for</span></span>, <span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>list</span></span>, ...</a></td></tr><tr><td align="right">3.19&nbsp;</td><td><a href="wcm.html" class="tocviewlink" data-pltdoc="x">Continuation Marks:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">with-<wbr></wbr>continuation-<wbr></wbr>mark</span></span></a></td></tr><tr><td align="right">3.20&nbsp;</td><td><a href="quasiquote.html" class="tocviewlink" data-pltdoc="x">Quasiquoting:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">quasiquote</span></span>, <span class="RktSym"><span class="RktStxLink">unquote</span></span>, and <span class="RktSym"><span class="RktStxLink">unquote-<wbr></wbr>splicing</span></span></a></td></tr><tr><td align="right">3.21&nbsp;</td><td><a href="Syntax_Quoting__quote-syntax.html" class="tocviewlink" data-pltdoc="x">Syntax Quoting:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">quote-<wbr></wbr>syntax</span></span></a></td></tr><tr><td align="right">3.22&nbsp;</td><td><a href="__top-interaction.html" class="tocviewlink" data-pltdoc="x">Interaction Wrapper:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">#%top-<wbr></wbr>interaction</span></span></a></td></tr><tr><td align="right">3.23&nbsp;</td><td><a href="block.html" class="tocviewlink" data-pltdoc="x">Blocks:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">block</span></span></a></td></tr><tr><td align="right">3.24&nbsp;</td><td><a href="stratified-body.html" class="tocviewlink" data-pltdoc="x">Internal-<wbr></wbr>Definition Limiting:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">#%stratified-<wbr></wbr>body</span></span></a></td></tr><tr><td align="right">3.25&nbsp;</td><td><a href="performance-hint.html" class="tocviewlink" data-pltdoc="x">Performance Hints:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">begin-<wbr></wbr>encourage-<wbr></wbr>inline</span></span></a></td></tr><tr><td align="right">3.26&nbsp;</td><td><a href="lazy-require.html" class="tocviewlink" data-pltdoc="x">Importing Modules Lazily:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">lazy-<wbr></wbr>require</span></span></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,&quot;tocview_2&quot;);">&#9658;</a></td><td>3.18&nbsp;</td><td><a href="for.html" class="tocviewselflink" data-pltdoc="x">Iterations and Comprehensions:<span class="mywbr"> &nbsp;</span> <span class="RktSym"><span class="RktStxLink">for</span></span>, <span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>list</span></span>, ...</a></td></tr></table><div class="tocviewsublistbottom" style="display: none;" id="tocview_2"><table cellspacing="0" cellpadding="0"><tr><td align="right">3.18.1&nbsp;</td><td><a href="for.html#%28part._.Iteration_and_.Comprehension_.Forms%29" class="tocviewlink" data-pltdoc="x">Iteration and Comprehension Forms</a></td></tr><tr><td align="right">3.18.2&nbsp;</td><td><a href="for.html#%28part._.Deriving_.New_.Iteration_.Forms%29" class="tocviewlink" data-pltdoc="x">Deriving New Iteration Forms</a></td></tr><tr><td align="right">3.18.3&nbsp;</td><td><a href="for.html#%28part._.Do_.Loops%29" class="tocviewlink" data-pltdoc="x">Do Loops</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><span class="tocsublinknumber">3.18.1<tt>&nbsp;</tt></span><a href="for.html#%28part._.Iteration_and_.Comprehension_.Forms%29" class="tocsubseclink" data-pltdoc="x">Iteration and Comprehension Forms</a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>list</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>vector</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhash%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>hash</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheq%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>hasheq</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheqv%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>hasheqv</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhashalw%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>hashalw</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>and</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>or</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fsum%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>sum</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fproduct%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>product</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flists%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>lists</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>first</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>last</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>fold</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>foldr</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flist%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>list</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flists%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>lists</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fvector%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>vector</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhash%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>hash</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhasheq%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>hasheq</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhasheqv%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>hasheqv</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhashalw%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>hashalw</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fand%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>and</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2For%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>or</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fsum%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>sum</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fproduct%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>product</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffirst%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>first</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flast%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>last</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>fold</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>foldr</span></span></a></td></tr><tr><td><span class="tocsublinknumber">3.18.2<tt>&nbsp;</tt></span><a href="for.html#%28part._.Deriving_.New_.Iteration_.Forms%29" class="tocsubseclink" data-pltdoc="x">Deriving New Iteration Forms</a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>fold/<span class="mywbr"> &nbsp;</span>derived</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>fold/<span class="mywbr"> &nbsp;</span>derived</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for/<span class="mywbr"> &nbsp;</span>foldr/<span class="mywbr"> &nbsp;</span>derived</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%2Fderived%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">for*/<span class="mywbr"> &nbsp;</span>foldr/<span class="mywbr"> &nbsp;</span>derived</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-sequence-syntax%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>sequence-<wbr></wbr>syntax</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">:<span class="mywbr"> &nbsp;</span>do-<wbr></wbr>in</span></span></a></td></tr><tr><td><a href="for.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-clause-syntax-protect%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">for-<wbr></wbr>clause-<wbr></wbr>syntax-<wbr></wbr>protect</span></span></a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-splicing-for-clause-syntax%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">define-<wbr></wbr>splicing-<wbr></wbr>for-<wbr></wbr>clause-<wbr></wbr>syntax</span></span></a></td></tr><tr><td><span class="tocsublinknumber">3.18.3<tt>&nbsp;</tt></span><a href="for.html#%28part._.Do_.Loops%29" class="tocsubseclink" data-pltdoc="x">Do Loops</a></td></tr><tr><td><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._do%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">do</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, &quot;8.6&quot;, &quot;../&quot;);"/></form>&nbsp;&nbsp;<a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;8.6&quot;);">top</a><span class="tocsettoggle">&nbsp;&nbsp;<a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright">&nbsp;&nbsp;<a href="set_.html" title="backward to &quot;3.17 Assignment: set! and set!-values&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="syntax.html" title="up to &quot;3 Syntactic Forms&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="wcm.html" title="forward to &quot;3.19 Continuation Marks: with-continuation-mark&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div><h4 x-source-module="(lib &quot;scribblings/reference/reference.scrbl&quot;)" x-source-pkg="racket-doc" x-part-tag="&quot;for&quot;">3.18<tt>&nbsp;</tt><a name="(part._for)"></a>Iterations and Comprehensions: <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>, ...</h4><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="finger.png" alt="+" width="24" height="24"/></span><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&amp;rel=for.html&amp;version=8.6" class="Sq" data-pltdoc="x">Iterations and Comprehensions</a> in <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&amp;rel=index.html&amp;version=8.6" class="Sq" data-pltdoc="x">The Racket Guide</a> introduces iterations and comprehensions.</p></blockquote></blockquote></blockquote><p>The <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> iteration forms are based on SRFI-42
[<a href="doc-bibliography.html#%28cite._.S.R.F.I-42%29" data-pltdoc="x">SRFI-42</a>].</p><h5 x-source-module="(lib &quot;scribblings/reference/reference.scrbl&quot;)" x-source-pkg="racket-doc" x-part-tag="&quot;Iteration_and_Comprehension_Forms&quot;">3.18.1<tt>&nbsp;</tt><a name="(part._.Iteration_and_.Comprehension_.Forms)"></a>Iteration and Comprehension Forms</h5><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/private/base..rkt)._for))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">for-clause</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">[</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktVar">seq-expr</span><span class="RktPn">]</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">seq-expr</span><span class="RktPn">]</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:when</span><span class="hspace">&nbsp;</span><span class="RktVar">guard-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:unless</span><span class="hspace">&nbsp;</span><span class="RktVar">guard-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:do</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktVar">do-body</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">]</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktVar">break-clause</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:splice</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">splicing-id</span><span class="hspace">&nbsp;</span><span class="RktPn">. </span><span class="RktVar">form</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">break-clause</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:break</span><span class="hspace">&nbsp;</span><span class="RktVar">guard-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:final</span><span class="hspace">&nbsp;</span><span class="RktVar">guard-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">body-or-break</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktVar">body</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktVar">break-clause</span></td></tr></table></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace">&nbsp;&nbsp;</span></td><td><span class="RktVar">seq-expr</span></td><td><span class="hspace">&nbsp;</span></td><td>:</td><td><span class="hspace">&nbsp;</span></td><td><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._sequence~3f%29%29" class="RktValLink" data-pltdoc="x">sequence?</a></span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Iteratively evaluates <span class="RktVar">body</span>s. The <span class="RktVar">for-clause</span>s
introduce bindings whose scope includes <span class="RktVar">body</span> and that
determine the number of times that <span class="RktVar">body</span> is evaluated.
A <span class="RktVar">break-clause</span> either among the <span class="RktVar">for-clause</span>s
or <span class="RktVar">body</span>s stops further iteration.</div></p><p>In the simple case, each <span class="RktVar">for-clause</span> has one of its first two
forms, where <span class="RktPn">[</span><span class="RktVar">id</span><span class="stt"> </span><span class="RktVar">seq-expr</span><span class="RktPn">]</span> is a shorthand for <span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">id</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktVar">seq-expr</span><span class="RktPn">]</span>. In this simple case, the <span class="RktVar">seq-expr</span>s are evaluated
left-to-right, and each must produce a sequence value (see
<a href="sequences.html" data-pltdoc="x">Sequences</a>).</p><p>The <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form iterates by drawing an element from each
sequence; if any sequence is empty, then the iteration stops, and
<a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&amp;rel=void_undefined.html&amp;version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#&lt;void&gt;</span></span></a> is the result of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> expression. Otherwise
a location is created for each <span class="RktVar">id</span> to hold the values of each
element; the sequence produced by a <span class="RktVar">seq-expr</span> must return as
many values for each iteration as corresponding <span class="RktVar">id</span>s.</p><p>The <span class="RktVar">id</span>s are then bound in the <span class="RktVar">body</span>, which is
evaluated, and whose results are ignored. Iteration continues with the
next element in each sequence and with fresh locations for each
<span class="RktVar">id</span>.</p><p>A <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form with zero <span class="RktVar">for-clause</span>s is equivalent to a
single <span class="RktVar">for-clause</span> that binds an unreferenced <span class="RktVar">id</span> to
a sequence containing a single element. All of the <span class="RktVar">id</span>s must
be distinct according to <span class="RktSym"><a href="stxcmp.html#%28def._%28%28quote._~23~25kernel%29._bound-identifier~3d~3f%29%29" class="RktValLink" data-pltdoc="x">bound-identifier=?</a></span>.</p><p>If any <span class="RktVar">for-clause</span> has the form <span class="RktPn">#:when</span><span class="stt"> </span><span class="RktVar">guard-expr</span>,
then only the preceding clauses (containing no <span class="RktPn">#:when</span>, <span class="RktPn">#:unless</span>, or <span class="RktPn">#:do</span>)
determine iteration as above, and the <span class="RktVar">body</span> is effectively
wrapped as</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._when%29%29" class="RktStxLink" data-pltdoc="x">when</a></span><span class="hspace">&nbsp;</span><span class="RktVar">guard-expr</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-patterns.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._......%252B%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">...+</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>using the remaining <span class="RktVar">for-clause</span>s. A <span class="RktVar">for-clause</span> of
the form <span class="RktPn">#:unless</span><span class="stt"> </span><span class="RktVar">guard-expr</span> corresponds to the same transformation
with <span class="RktSym"><a href="when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._unless%29%29" class="RktStxLink" data-pltdoc="x">unless</a></span> in place of <span class="RktSym"><a href="when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._when%29%29" class="RktStxLink" data-pltdoc="x">when</a></span>. A <span class="RktVar">for-clause</span> of
the form <span class="RktPn">#:do</span><span class="stt"> </span><span class="RktPn">[</span><span class="RktVar">do-body</span><span class="stt"> </span><span class="RktMeta"><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> similarly creates nesting and
corresponds to</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><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">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">do-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-patterns.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._......%252B%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">...+</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>where the <span class="RktVar">do-body</span> forms may introduce definitions that are
visible in the remaining <span class="RktVar">for-clause</span>s.</p><p>A <span class="RktPn">#:break</span><span class="stt"> </span><span class="RktVar">guard-expr</span> clause is similar to a
<span class="RktPn">#:unless</span><span class="stt"> </span><span class="RktVar">guard-expr</span> clause, but when <span class="RktPn">#:break</span>
avoids evaluation of the <span class="RktVar">body</span>s, it also effectively ends all
sequences within the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form. A <span class="RktPn">#:final</span><span class="stt"> </span><span class="RktVar">guard-expr</span> clause is similar to <span class="RktPn">#:break</span><span class="stt"> </span><span class="RktVar">guard-expr</span>, but
instead of immediately ending sequences and skipping the
<span class="RktVar">body</span>s, it allows at most one more element from each later
sequence and at most one more evaluation of the following
<span class="RktVar">body</span>s. Among the <span class="RktVar">body</span>s, besides stopping the
iteration and preventing later <span class="RktVar">body</span> evaluations, a
<span class="RktPn">#:break</span><span class="stt"> </span><span class="RktVar">guard-expr</span> or <span class="RktPn">#:final</span><span class="stt"> </span><span class="RktVar">guard-expr</span>
clause starts a new internal-definition context.</p><p>A <span class="RktPn">#:splice</span><span class="stt"> </span><span class="RktPn">(</span><span class="RktVar">splicing-id</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">form</span><span class="RktPn">)</span> clause is replaced by the
sequence of forms that are produced by expanding <span class="RktPn">(</span><span class="RktVar">splicing-id</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">form</span><span class="RktPn">)</span>, where <span class="RktVar">splicing-id</span> is bound using
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-splicing-for-clause-syntax%29%29" class="RktStxLink" data-pltdoc="x">define-splicing-for-clause-syntax</a></span>. The binding context of
that expansion includes previous binding from any clause preceding
both the <span class="RktPn">#:splice</span> form and a <span class="RktPn">#:when</span>,
<span class="RktPn">#:unless</span>, <span class="RktPn">#:do</span>, <span class="RktPn">#:break</span>, or
<span class="RktPn">#:final</span> form. The result of a <span class="RktPn">#:splice</span> expansion can
include more <span class="RktPn">#:splice</span> forms to further interleave clause
binding and expansion. Support for <span class="RktPn">#:splicing</span> clauses is
intended less for direct use in source <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> forms than for
building new forms that expand to <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>.</p><p>In the case of <a href="pairs.html#%28tech._list%29" class="techoutside" data-pltdoc="x"><span class="techinside">list</span></a> and <a href="streams.html#%28tech._stream%29" class="techoutside" data-pltdoc="x"><span class="techinside">stream</span></a> sequences, the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form itself does not keep each element reachable. If a
list or stream produced by a <span class="RktVar">seq-expr</span> is otherwise
unreachable, and if the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> body can no longer reference an
<span class="RktVar">id</span> for a list element, then the element is subject to
<a href="eval-model.html#%28tech._garbage._collection%29" class="techoutside" data-pltdoc="x"><span class="techinside">garbage collection</span></a>. The <span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._make-do-sequence%29%29" class="RktValLink" data-pltdoc="x">make-do-sequence</a></span> sequence
constructor supports additional sequences that behave like lists and
streams in this way.</p><p>If a <span class="RktVar">seq-expr</span> is a quoted literal list, vector, exact integer,
string, byte string, immutable hash, or expands to such a literal,
then it may be treated as if a sequence transformer such as
<span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span> was used, unless the <span class="RktVar">seq-expr</span> has a true
value for the <a name="(idx._(gentag._110._(lib._scribblings/reference/reference..scrbl)))"></a><span class="RktVal">'</span><span class="RktVal">for:no-implicit-optimization</span> syntax
property; in most cases this improves performance.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(1 a #t)(1 a #f)(3 c #t)(3 c #f)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:do</span><span class="hspace">&nbsp;</span><span class="RktPn">[</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">&nbsp;</span><span class="RktSym">neg-i</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal"><span class="nobreak">-1</span></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">neg-i</span><span class="hspace">&nbsp;</span><span class="RktVal">0</span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">j</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(-1)(0)(1)(-2)(0)(2)(-3)(0)(3)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">#hash</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktVal">"a"</span><span class="hspace">&nbsp;</span><span class="RktPn">. </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVal">"b"</span><span class="hspace">&nbsp;</span><span class="RktPn">. </span><span class="RktVal">20</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(a 1)(b 20)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:break</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(1 a #t)(1 a #f)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:final</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(1 a #t)(1 a #f)(2 b #t)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:break</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._or%29%29" class="RktStxLink" data-pltdoc="x">or</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(1 a #t)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"here"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">here</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.7.0.4 of package <span class="stt">base</span>: Added support for the optional second result.<br/>Changed in version 7.8.0.11: Added support for implicit optimization.<br/>Changed in version 8.4.0.2: Added <span class="RktPn">#:do</span>.<br/>Changed in version 8.4.0.3: Added <span class="RktPn">#:splice</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/list))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/list</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"> Iterates like
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but that the last expression in the <span class="RktVar">body</span>s must
produce a single value, and the result of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>
expression is a list of the results in order.
When evaluation of a <span class="RktVar">body</span> is skipped due to a <span class="RktPn">#:when</span>
or <span class="RktPn">#:unless</span> clause, the result list includes no corresponding
element.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'((1 #\a #t) (1 #\a #f) (3 #\c #t) (3 #\c #f))</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:break</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'((1 #\a #t) (1 #\a #f))</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">any</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(any)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'()</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/private/base..rkt)._for/vector))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/vector</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-length</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-length</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</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">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:length</span><span class="hspace">&nbsp;</span><span class="RktVar">length-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:length</span><span class="hspace">&nbsp;</span><span class="RktVar">length-expr</span><span class="hspace">&nbsp;</span><span class="RktPn">#:fill</span><span class="hspace">&nbsp;</span><span class="RktVar">fill-expr</span></td></tr></table></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace">&nbsp;&nbsp;</span></td><td><span class="RktVar">length-expr</span></td><td><span class="hspace">&nbsp;</span></td><td>:</td><td><span class="hspace">&nbsp;</span></td><td><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></td></tr></table></blockquote></div><div class="SIntrapara">Iterates like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>, but results are accumulated into
a vector instead of a list.</div></p><p>If the optional <span class="RktPn">#:length</span> clause is specified, the result of
<span class="RktVar">length-expr</span> determines the length of the result vector. In
that case, the iteration can be performed more efficiently, and it
terminates when the vector is full or the requested number of
iterations have been performed, whichever comes first. If
<span class="RktVar">length-expr</span> specifies a length longer than the number of
iterations, then the remaining slots of the vector are initialized to
the value of <span class="RktVar">fill-expr</span>, which defaults to <span class="RktVal">0</span> (i.e.,
the default argument of <span class="RktSym"><a href="vectors.html#%28def._%28%28quote._~23~25kernel%29._make-vector%29%29" class="RktValLink" data-pltdoc="x">make-vector</a></span>).</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxLink" data-pltdoc="x">for/vector</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'#("1" "2" "3")</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxLink" data-pltdoc="x">for/vector</a></span><span class="hspace">&nbsp;</span><span class="RktPn">#:length</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'#("1" "2")</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxLink" data-pltdoc="x">for/vector</a></span><span class="hspace">&nbsp;</span><span class="RktPn">#:length</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'#("1" "2" "3" 0)</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxLink" data-pltdoc="x">for/vector</a></span><span class="hspace">&nbsp;</span><span class="RktPn">#:length</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktPn">#:fill</span><span class="hspace">&nbsp;</span><span class="RktVal">"?"</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'#("1" "2" "3" "?")</span></p></td></tr></table></blockquote></div></p><p>The <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fvector%29%29" class="RktStxLink" data-pltdoc="x">for/vector</a></span> form may allocate a vector and mutate it after
each iteration of <span class="RktVar">body</span>, which means that capturing a
continuation during <span class="RktVar">body</span> and applying it multiple times may
mutate a shared vector.</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/hash))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhash%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/hash</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/hasheq))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheq%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/hasheq</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/hasheqv))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheqv%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/hasheqv</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/hashalw))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhashalw%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/hashalw</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>, but the result is an immutable <a href="hashtables.html#%28tech._hash._table%29" class="techoutside" data-pltdoc="x"><span class="techinside">hash
table</span></a>; <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhash%29%29" class="RktStxLink" data-pltdoc="x">for/hash</a></span> creates a table using <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> to
distinguish keys, <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheq%29%29" class="RktStxLink" data-pltdoc="x">for/hasheq</a></span> produces a table using
<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>, <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhasheqv%29%29" class="RktStxLink" data-pltdoc="x">for/hasheqv</a></span> produces a table 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>, and <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhashalw%29%29" class="RktStxLink" data-pltdoc="x">for/hashalw</a></span> produces a table using
<span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal-always~3f%29%29" class="RktValLink" data-pltdoc="x">equal-always?</a></span>.
The last expression in the <span class="RktVar">body</span>s must return
two values: a key and a value to extend the hash table accumulated by
the iteration.</div></p><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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhash%29%29" class="RktStxLink" data-pltdoc="x">for/hash</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'#hash((1 . "1") (2 . "2") (3 . "3"))</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 8.5.0.3 of package <span class="stt">base</span>: Added the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fhashalw%29%29" class="RktStxLink" data-pltdoc="x">for/hashalw</a></span> form.</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/private/base..rkt)._for/and))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/and</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"> Iterates like
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but when last expression of <span class="RktVar">body</span> produces
<span class="RktVal">#f</span>, then iteration terminates, and the result of the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span> expression is <span class="RktVal">#f</span>. If the <span class="RktVar">body</span>
is never evaluated, then the result of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span>
expression is <span class="RktVal">#t</span>. Otherwise, the result is the (single)
result from the last evaluation of <span class="RktVar">body</span>.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">"x"</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktPn">. </span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3c%29%29" class="RktValLink" data-pltdoc="x">&lt;</a></span><span class="RktPn"> .</span><span class="hspace">&nbsp;</span><span class="RktVal">3</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">4</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:break</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fand%29%29" class="RktStxLink" data-pltdoc="x">for/and</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</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><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/private/base..rkt)._for/or))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/or</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"> Iterates like
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but when last expression of <span class="RktVar">body</span> produces
a value other than <span class="RktVal">#f</span>, then iteration terminates, and
the result of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxLink" data-pltdoc="x">for/or</a></span> expression is the same
(single) value. If the <span class="RktVar">body</span> is never evaluated, then the
result of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxLink" data-pltdoc="x">for/or</a></span> expression is
<span class="RktVal">#f</span>. Otherwise, the result is <span class="RktVal">#f</span>.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxLink" data-pltdoc="x">for/or</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">"x"</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktPn">. </span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3c%29%29" class="RktValLink" data-pltdoc="x">&lt;</a></span><span class="RktPn"> .</span><span class="hspace">&nbsp;</span><span class="RktVal">3</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><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxLink" data-pltdoc="x">for/or</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">1</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2For%29%29" class="RktStxLink" data-pltdoc="x">for/or</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</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></table></blockquote></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/sum))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fsum%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/sum</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Iterates like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but each result of the last <span class="RktVar">body</span>
is accumulated into a result with <span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span>.</div></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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fsum%29%29" class="RktStxLink" data-pltdoc="x">for/sum</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">10</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><table cellspacing="0" cellpadding="0" class="together"><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/private/base..rkt)._for/product))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fproduct%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/product</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Iterates like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but each result of the last <span class="RktVar">body</span>
is accumulated into a result with <span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span>.</div></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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Fproduct%29%29" class="RktStxLink" data-pltdoc="x">for/product</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">24</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><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/lists))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flists%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/lists</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-result</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</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">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktVar">result-expr</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>, but the last <span class="RktVar">body</span> expression
should produce as many values as given <span class="RktVar">id</span>s.
The <span class="RktVar">id</span>s are bound to
the reversed lists accumulated so far in the <span class="RktVar">for-clause</span>s and
<span class="RktVar">body</span>s.</div></p><p>If a <span class="RktVar">result-expr</span> is provided, it is used as with <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>
when iteration terminates;
otherwise, the result is as many lists as supplied <span class="RktVar">id</span>s.</p><p>The scope of <span class="RktVar">id</span> bindings is the same as for accumulator
identifiers in <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>. Mutating a <span class="RktVar">id</span> affects the
accumulated lists, and mutating it in a way that produces a non-list
can cause a final <span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Flist..rkt%29._reverse%29%29" class="RktValLink" data-pltdoc="x">reverse</a></span> for each <span class="RktVar">id</span> to fail.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flists%29%29" class="RktStxLink" data-pltdoc="x">for/lists</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">l1</span><span class="hspace">&nbsp;</span><span class="RktSym">l2</span><span class="hspace">&nbsp;</span><span class="RktSym">l3</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"abc"</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">#t</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktRes">'(1 1 3 3)</span></p></td></tr><tr><td><p><span class="RktRes">'(#\a #\a #\c #\c)</span></p></td></tr><tr><td><p><span class="RktRes">'(#t #f #t #f)</span></p></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flists%29%29" class="RktStxLink" data-pltdoc="x">for/lists</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">acc</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">tvp</span><span class="hspace">&nbsp;</span><span class="RktVal">tofu</span><span class="hspace">&nbsp;</span><span class="RktVal">seitan</span><span class="hspace">&nbsp;</span><span class="RktVal">tvp</span><span class="hspace">&nbsp;</span><span class="RktVal">tofu</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:unless</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._member%29%29" class="RktValLink" data-pltdoc="x">member</a></span><span class="hspace">&nbsp;</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(tvp tofu seitan)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flists%29%29" class="RktStxLink" data-pltdoc="x">for/lists</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">firsts</span><span class="hspace">&nbsp;</span><span class="RktSym">seconds</span><span class="hspace">&nbsp;</span><span class="RktPn">#:result</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">firsts</span><span class="hspace">&nbsp;</span><span class="RktSym">seconds</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">pr</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">. </span><span class="RktVal">2</span><span class="RktVal">)</span><span class="hspace">&nbsp;</span><span class="RktVal">(</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">. </span><span class="RktVal">4</span><span class="RktVal">)</span><span class="hspace">&nbsp;</span><span class="RktVal">(</span><span class="RktVal">5</span><span class="hspace">&nbsp;</span><span class="RktVal">. </span><span class="RktVal">6</span><span class="RktVal">)</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._car%29%29" class="RktValLink" data-pltdoc="x">car</a></span><span class="hspace">&nbsp;</span><span class="RktSym">pr</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._cdr%29%29" class="RktValLink" data-pltdoc="x">cdr</a></span><span class="hspace">&nbsp;</span><span class="RktSym">pr</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'((1 3 5) (2 4 6))</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 7.1.0.2 of package <span class="stt">base</span>: Added the <span class="RktPn">#:result</span> form.</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/private/base..rkt)._for/first))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/first</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"> Iterates like
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but after <span class="RktVar">body</span> is evaluated the first
time, then the iteration terminates, and the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="RktStxLink" data-pltdoc="x">for/first</a></span>
result is the (single) result of <span class="RktVar">body</span>. If the
<span class="RktVar">body</span> is never evaluated, then the result of the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="RktStxLink" data-pltdoc="x">for/first</a></span> expression is <span class="RktVal">#f</span>.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="RktStxLink" data-pltdoc="x">for/first</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">"x"</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">"2"</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffirst%29%29" class="RktStxLink" data-pltdoc="x">for/first</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</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></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/private/base..rkt)._for/last))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/last</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara"> Iterates like
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="RktStxLink" data-pltdoc="x">for/last</a></span> result is the (single)
result of the last evaluation of <span class="RktVar">body</span>. If the
<span class="RktVar">body</span> is never evaluated, then the result of the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="RktStxLink" data-pltdoc="x">for/last</a></span> expression is <span class="RktVal">#f</span>.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="RktStxLink" data-pltdoc="x">for/last</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktVal">5</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;</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-&gt;string</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">"4"</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flast%29%29" class="RktStxLink" data-pltdoc="x">for/last</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._error%29%29" class="RktValLink" data-pltdoc="x">error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"doesn't get here"</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></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><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/fold))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/fold</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-result</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</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">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktVar">result-expr</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Iterates like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>. Before iteration starts, the
<span class="RktVar">init-expr</span>s are evaluated to produce initial accumulator
values. At the start of each iteration, a location is generated
for each <span class="RktVar">accum-id</span>, and the corresponding current accumulator
value is placed into the location. The last expression in
<span class="RktVar">body</span> must produce as many values as <span class="RktVar">accum-id</span>s, and
those values become the current accumulator values. When iteration
terminates, if a <span class="RktVar">result-expr</span> is provided then the result of the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span> is the result of evaluating <span class="RktVar">result-expr</span>
(with <span class="RktVar">accum-id</span>s in scope and bound to their final values),
otherwise the results of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span> expression are the
accumulator values.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">sum</span><span class="hspace">&nbsp;</span><span class="RktVal">0</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">rev-roots</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._null%29%29" class="RktValLink" data-pltdoc="x">null</a></span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</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">&nbsp;</span><span class="RktSym">sum</span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sqrt%29%29" class="RktValLink" data-pltdoc="x">sqrt</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">rev-roots</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"><tr><td><p><span class="RktRes">10</span></p></td></tr><tr><td><p><span class="RktRes">'(2 1.7320508075688772 1.4142135623730951 1)</span></p></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">seen</span><span class="hspace">&nbsp;</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="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Flist..rkt%29._reverse%29%29" class="RktValLink" data-pltdoc="x">reverse</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">0</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</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">&nbsp;</span><span class="RktSym">seen</span><span class="hspace">&nbsp;</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktSym">seen</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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><span class="hspace">&nbsp;</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">&nbsp;</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">&nbsp;</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="hashtables.html#%28def._%28%28quote._~23~25kernel%29._hash-set%29%29" class="RktValLink" data-pltdoc="x">hash-set</a></span><span class="hspace">&nbsp;</span><span class="RktSym">seen</span><span class="hspace">&nbsp;</span><span class="RktSym">x</span><span class="hspace">&nbsp;</span><span class="RktVal">#t</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><p><span class="RktRes">'(0 1 2 3 4)</span></p></td></tr></table></blockquote></div></p><p>The binding and evaluation order of <span class="RktVar">accum-id</span>s and
<span class="RktVar">init-expr</span>s do not completely follow the textual,
left-to-right order relative to the <span class="RktVar">for-clause</span>s. Instead, the
sequence expressions in <span class="RktVar">for-clause</span>s that determine the
outermost iteration are evaluated first, then the <span class="RktVar">init-expr</span>s
are evaluated and the <span class="RktVar">accum-id</span>s are bound, and finally the
outermost iteration&rsquo;s identifiers are bound. One consequence is that
the <span class="RktVar">accum-id</span>s are not bound in <span class="RktVar">for-clause</span>s for the
outermost initialization. At the same time, when a <span class="RktVar">accum-id</span>
is used as a <span class="RktVar">for-clause</span> binding for the outermost iteration,
the <span class="RktVar">for-clause</span> binding shadows the <span class="RktVar">accum-id</span> binding
in the loop body (which is what you would expect syntactically).
A fresh variable for each <span class="RktVar">accum-id</span> (at a
fresh location) is bound in each nested iteration that is created by a
later group for <span class="RktVar">for-clause</span>s (after a <span class="RktPn">#:when</span> or
<span class="RktPn">#:unless</span>, for example).</p><p class="SHistory">Changed in version 6.11.0.1 of package <span class="stt">base</span>: Added the <span class="RktPn">#:result</span> form.</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/private/base..rkt)._for/foldr))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/foldr</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">accum-option</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">accum-option</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktVar">result-expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:delay</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:delay-as</span><span class="hspace">&nbsp;</span><span class="RktVar">delayed-id</span></td></tr><tr><td align="right" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktPn">#:delay-with</span><span class="hspace">&nbsp;</span><span class="RktVar">delayer-id</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>, but analogous to <span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Flist..rkt%29._foldr%29%29" class="RktValLink" data-pltdoc="x">foldr</a></span> rather than
<span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Flist..rkt%29._foldl%29%29" class="RktValLink" data-pltdoc="x">foldl</a></span>: the given sequences are still iterated in the same order, but
the loop body is evaluated in reverse order. Evaluation of a <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span>
expression uses space proportional to the number of iterations it performs, and
all elements produced by the given sequences are retained until backwards
evaluation of the loop body begins (assuming the element is, in fact,
referenced in the body).</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">&gt; </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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">in-printing</span><span class="hspace">&nbsp;</span><span class="RktSym">seq</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fsequence..rkt%29._sequence-map%29%29" class="RktValLink" data-pltdoc="x">sequence-map</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._println%29%29" class="RktValLink" data-pltdoc="x">println</a></span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">seq</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">in-printing</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-range%29%29" class="RktValLink" data-pltdoc="x">in-range</a></span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._println%29%29" class="RktValLink" data-pltdoc="x">println</a></span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktOut">1</span></p></td></tr><tr><td><p><span class="RktOut">2</span></p></td></tr><tr><td><p><span class="RktOut">3</span></p></td></tr><tr><td><p><span class="RktOut">3</span></p></td></tr><tr><td><p><span class="RktOut">2</span></p></td></tr><tr><td><p><span class="RktOut">1</span></p></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(1 2 3)</span></p></td></tr></table></blockquote></div></p><p>Furthermore, unlike <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>, the <span class="RktVar">accum-id</span>s are not bound
within <span class="RktVar">guard-expr</span>s or <span class="RktVar">body-or-break</span> forms that appear before
a <span class="RktVar">break-clause</span>.</p><p>While the aforementioned limitations make <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span> less generally
useful than <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>, <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span> provides the additional
capability to iterate lazily via the <span class="RktPn">#:delay</span>, <span class="RktPn">#:delay-as</span>, and
<span class="RktPn">#:delay-with</span> options, which can mitigate many of <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span>&rsquo;s
disadvantages. If at least one such option is specified, the loop body is given
explicit control over when iteration continues: by default, each
<span class="RktVar">accum-id</span> is bound to a <a href="Delayed_Evaluation.html#%28tech._promise%29" class="techoutside" data-pltdoc="x"><span class="techinside">promise</span></a> that, when forced, produces the
<span class="RktVar">accum-id</span>&rsquo;s current value.</p><p>In this mode, iteration does not continue until one such promise is forced,
which triggers any additional iteration necessary to produce a value. If the
loop body is lazy in its <span class="RktVar">accum-id</span>s&#8212;<wbr></wbr>that is, it returns a value
without forcing any of them&#8212;<wbr></wbr>then the loop (or any of its iterations) will
produce a value before iteration has completely finished. If a reference to at
least one such promise is retained, then forcing it will resume iteration from
the point at which it was suspended, even if control has left the dynamic extent
of the loop body.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:delay</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-range%29%29" class="RktValLink" data-pltdoc="x">in-range</a></span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktVal">"--&gt; ~v\n"</span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin0%29%29" class="RktStxLink" data-pltdoc="x">begin0</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktVal">"&lt;-- ~v\n"</span><span class="hspace">&nbsp;</span><span class="RktSym">v</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"><tr><td><p><span class="RktOut">--&gt; 1</span></p></td></tr><tr><td><p><span class="RktOut">--&gt; 2</span></p></td></tr><tr><td><p><span class="RktOut">--&gt; 3</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 3</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 2</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 1</span></p></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(1 2 3)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </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">&nbsp;</span><span class="RktSym">resume</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:delay</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-range%29%29" class="RktValLink" data-pltdoc="x">in-range</a></span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">5</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktVal">"--&gt; ~v\n"</span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin0%29%29" class="RktStxLink" data-pltdoc="x">begin0</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3d%29%29" class="RktValLink" data-pltdoc="x">=</a></span><span class="hspace">&nbsp;</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">v</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktVal">"&lt;-- ~v\n"</span><span class="hspace">&nbsp;</span><span class="RktSym">v</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"><tr><td><p><span class="RktOut">--&gt; 1</span></p></td></tr><tr><td><p><span class="RktOut">--&gt; 2</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 2</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 1</span></p></td></tr></table></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">resume</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td><p><span class="RktOut">--&gt; 3</span></p></td></tr><tr><td><p><span class="RktOut">--&gt; 4</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 4</span></p></td></tr><tr><td><p><span class="RktOut">&lt;-- 3</span></p></td></tr></table></td></tr><tr><td><p><span class="RktRes">'(3 4)</span></p></td></tr></table></blockquote></div></p><p>This extra control over iteration order allows <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span> to both
consume and construct infinite sequences, so long as it is at least sometimes
lazy in its accumulators.</p><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="magnify.png" alt="+" width="24" height="24"/></span>See also <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2Fstream%29%29" class="RktStxLink" data-pltdoc="x">for/stream</a></span> for a more convenient (albeit less flexible) way
to lazily transform infinite sequences. (Internally, <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2Fstream%29%29" class="RktStxLink" data-pltdoc="x">for/stream</a></span> is
defined in terms of <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span>.)</p></blockquote></blockquote></blockquote><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">&gt; </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">&nbsp;</span><span class="RktSym">squares</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">s</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._empty-stream%29%29" class="RktValLink" data-pltdoc="x">empty-stream</a></span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:delay</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-naturals%29%29" class="RktValLink" data-pltdoc="x">in-naturals</a></span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-cons%29%29" class="RktStxLink" data-pltdoc="x">stream-cons</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-~3elist%29%29" class="RktValLink" data-pltdoc="x">stream-&gt;list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-take%29%29" class="RktValLink" data-pltdoc="x">stream-take</a></span><span class="hspace">&nbsp;</span><span class="RktSym">squares</span><span class="hspace">&nbsp;</span><span class="RktVal">10</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(0 1 4 9 16 25 36 49 64 81)</span></p></td></tr></table></blockquote></div></p><p>The suspension introduced by the <span class="RktPn">#:delay</span> option does not ordinarily
affect the loop&rsquo;s eventual return value, but if <span class="RktPn">#:delay</span> and
<span class="RktPn">#:result</span> are combined, the <span class="RktVar">accum-id</span>s will be delayed in the
scope of the <span class="RktVar">result-expr</span> in the same way they are delayed within the
loop body. This can be used to introduce an additional layer of suspension
around the evaluation of the entire loop, if desired.</p><p><div class="SIntrapara"><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </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">&nbsp;</span><span class="RktSym">evaluated-yet?</span><span class="hspace">&nbsp;</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace">&nbsp;</span><span class="RktSym">evaluated-yet?</span><span class="hspace">&nbsp;</span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:delay</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">&gt; </span><span class="RktSym">evaluated-yet?</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></div></p></div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </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">&nbsp;</span><span class="RktSym">evaluated-yet?</span><span class="hspace">&nbsp;</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">&gt; </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">&nbsp;</span><span class="RktSym">start</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">acc</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace">&nbsp;</span><span class="RktSym">evaluated-yet?</span><span class="hspace">&nbsp;</span><span class="RktVal">#t</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:delay</span><span class="hspace">&nbsp;</span><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">acc</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">&gt; </span><span class="RktSym">evaluated-yet?</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="Delayed_Evaluation.html#%28def._%28%28lib._racket%2Fpromise..rkt%29._force%29%29" class="RktValLink" data-pltdoc="x">force</a></span><span class="hspace">&nbsp;</span><span class="RktSym">start</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">&gt; </span><span class="RktSym">evaluated-yet?</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></div></p><p>If the <span class="RktPn">#:delay-as</span> option is provided, then <span class="RktVar">delayed-id</span> is
bound to an additional promise that returns the values of all <span class="RktVar">accum-id</span>s
at once. When multiple <span class="RktVar">accum-id</span>s are provided, forcing this promise can
be slightly more efficient than forcing the promises bound to the
<span class="RktVar">accum-id</span>s individually.</p><p>If the <span class="RktPn">#:delay-with</span> option is provided, the given <span class="RktVar">delayer-id</span>
is used to suspend nested iterations (instead of the default, <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%29%29" class="RktStxLink" data-pltdoc="x">delay</a></span>).
A form of the shape <span class="RktPn">(</span><span class="RktVar">delayer-id</span><span class="stt"> </span><span class="RktVar">recur-expr</span><span class="RktPn">)</span> is constructed and placed
in expression position, where <span class="RktVar">recur-expr</span> is an expression that, when
evaluated, will perform the next iteration and return its result (or results).
Sensible choices for <span class="RktVar">delayer-id</span> include <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._lazy%29%29" class="RktStxLink" data-pltdoc="x">lazy</a></span>,
<span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fsync%29%29" class="RktStxLink" data-pltdoc="x">delay/sync</a></span>, <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fthread%29%29" class="RktStxLink" data-pltdoc="x">delay/thread</a></span>, or any of the other promise
constructors from <a href="Delayed_Evaluation.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/promise</span></a>, as well as <span class="RktSym"><a href="procedures.html#%28form._%28%28lib._racket%2Ffunction..rkt%29._thunk%29%29" class="RktStxLink" data-pltdoc="x">thunk</a></span> from
<a href="procedures.html#%28mod-path._racket%2Ffunction%29" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/function</span></a>. However, beware that choices such as
<span class="RktSym"><a href="procedures.html#%28form._%28%28lib._racket%2Ffunction..rkt%29._thunk%29%29" class="RktStxLink" data-pltdoc="x">thunk</a></span> or <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fname%29%29" class="RktStxLink" data-pltdoc="x">delay/name</a></span> may evaluate their subexpression multiple
times, which can lead to nonsensical results for sequences that have state, as
the state will be shared between all evaluations of the <span class="RktVar">recur-expr</span>.</p><p>If multiple <span class="RktVar">accum-id</span>s are given, the <span class="RktPn">#:delay-with</span> option is
provided, and <span class="RktVar">delayer-id</span> is not bound to one of <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%29%29" class="RktStxLink" data-pltdoc="x">delay</a></span>,
<span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._lazy%29%29" class="RktStxLink" data-pltdoc="x">lazy</a></span>, <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fstrict%29%29" class="RktStxLink" data-pltdoc="x">delay/strict</a></span>, <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fsync%29%29" class="RktStxLink" data-pltdoc="x">delay/sync</a></span>,
<span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fthread%29%29" class="RktStxLink" data-pltdoc="x">delay/thread</a></span>, or <span class="RktSym"><a href="Delayed_Evaluation.html#%28form._%28%28lib._racket%2Fpromise..rkt%29._delay%2Fidle%29%29" class="RktStxLink" data-pltdoc="x">delay/idle</a></span>, the <span class="RktVar">accum-id</span>s will not
be bound at all, even within the loop body. Instead, the <span class="RktPn">#:delay-as</span>
option must be specified to access the accumulator values via
<span class="RktVar">delayed-id</span>.</p><p class="SHistory">Added in version 7.3.0.3 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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, but with an implicit <span class="RktPn">#:when</span><span class="stt"> </span><span class="RktVal">#t</span> between
each pair of <span class="RktSym">for-clauses</span>, so that all sequence iterations are
nested.</div></p><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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%29%29" class="RktStxLink" data-pltdoc="x">for*</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"ab"</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._display%29%29" class="RktValLink" data-pltdoc="x">display</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">(1 a)(1 b)(2 a)(2 b)</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><table cellspacing="0" cellpadding="0" class="together"><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/private/base..rkt)._for*/list))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flist%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/list</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/lists))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flists%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/lists</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/vector))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fvector%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/vector</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-length</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/hash))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhash%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/hash</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/hasheq))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhasheq%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/hasheq</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/hasheqv))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhasheqv%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/hasheqv</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/hashalw))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhashalw%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/hashalw</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/and))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fand%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/and</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/or))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2For%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/or</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/sum))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fsum%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/sum</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/product))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fproduct%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/product</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/first))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffirst%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/first</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/last))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flast%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/last</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/fold))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/fold</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/foldr))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/foldr</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">accum-option</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span>, etc., but with the implicit nesting of
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%29%29" class="RktStxLink" data-pltdoc="x">for*</a></span>.</div></p><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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for*/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktVal">"ab"</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">j</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">'((1 #\a) (1 #\b) (2 #\a) (2 #\b))</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 7.3.0.3 of package <span class="stt">base</span>: Added the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for*/foldr</a></span> form.<br/>Changed in version 8.5.0.3: Added the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Fhashalw%29%29" class="RktStxLink" data-pltdoc="x">for*/hashalw</a></span> form.</p><h5 x-source-module="(lib &quot;scribblings/reference/reference.scrbl&quot;)" x-source-pkg="racket-doc" x-part-tag="&quot;Deriving_New_Iteration_Forms&quot;">3.18.2<tt>&nbsp;</tt><a name="(part._.Deriving_.New_.Iteration_.Forms)"></a>Deriving New Iteration Forms</h5><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/private/base..rkt)._for/fold/derived))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/fold/derived</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">orig-datum</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for/fold</a></span>, but the extra <span class="RktVar">orig-datum</span> is used as the
source for all syntax errors.</div></p><p>A macro that expands to <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for/fold/derived</a></span> should typically use
<span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Parsing_for_Bodies.html%23%2528def._%2528%2528lib._syntax%252Ffor-body..rkt%2529._split-for-body%2529%2529&amp;version=8.6" class="RktValLink Sq" data-pltdoc="x">split-for-body</a></span> to handle the possibility of macros and other
definitions mixed with keywords like <span class="RktPn">#:break</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-syntax%29%29" class="RktStxLink" data-pltdoc="x">for-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktSym">syntax/for-body</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">syntax/parse/define</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Defining_Simple_Macros.html%23%2528form._%2528%2528lib._syntax%252Fparse%252Fdefine..rkt%2529._define-syntax-parse-rule%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-syntax-parse-rule</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">for/digits</span><span class="hspace">&nbsp;</span><span class="RktSym">clauses</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktSym">original</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Parsing_for_Bodies.html%23%2528def._%2528%2528lib._syntax%252Ffor-body..rkt%2529._split-for-body%2529%2529&amp;version=8.6" class="RktValLink Sq" data-pltdoc="x">split-for-body</a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for/fold/derived</a></span><span class="hspace">&nbsp;</span><span class="RktSym">original</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktVal">0</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">clauses</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</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">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">10</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="RktCmt">;</span><span class="RktCmt">&nbsp;</span><span class="RktCmt">If we misuse for/digits, we can get good error reporting</span></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt">&nbsp;</span><span class="RktCmt">because the use of orig-datum allows for source correlation:</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym">for/digits</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">a</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">b</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktVal">5</span><span class="hspace">&nbsp;</span><span class="RktVal">6</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">a</span><span class="hspace">&nbsp;</span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">eval:4:0: for/digits: bad sequence binding clause</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace">&nbsp;&nbsp;</span><span class="RktErr">at: a</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace">&nbsp;&nbsp;</span><span class="RktErr">in: (for/digits (a (in-list (quote (1 2 3)))) (b (in-list</span></p></td></tr><tr><td><p><span class="RktErr">(quote (4 5 6)))) (+ a b))</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym">for/digits</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">a</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">b</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">2</span><span class="hspace">&nbsp;</span><span class="RktVal">4</span><span class="hspace">&nbsp;</span><span class="RktVal">6</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">a</span><span class="hspace">&nbsp;</span><span class="RktSym">b</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">963</span></p></td></tr><tr><td><span class="RktCmt">;</span><span class="RktCmt">&nbsp;</span><span class="RktCmt">Another example: compute the max during iteration:</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Defining_Simple_Macros.html%23%2528form._%2528%2528lib._syntax%252Fparse%252Fdefine..rkt%2529._define-syntax-parse-rule%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-syntax-parse-rule</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">for/max</span><span class="hspace">&nbsp;</span><span class="RktSym">clauses</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktSym">original</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Parsing_for_Bodies.html%23%2528def._%2528%2528lib._syntax%252Ffor-body..rkt%2529._split-for-body%2529%2529&amp;version=8.6" class="RktValLink Sq" data-pltdoc="x">split-for-body</a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for/fold/derived</a></span><span class="hspace">&nbsp;</span><span class="RktSym">original</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">current-max</span><span class="hspace">&nbsp;</span><span class="RktVal"><span class="nobreak">-i</span>nf.0</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">clauses</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">maybe-new-max</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3e%29%29" class="RktValLink" data-pltdoc="x">&gt;</a></span><span class="hspace">&nbsp;</span><span class="RktSym">maybe-new-max</span><span class="hspace">&nbsp;</span><span class="RktSym">current-max</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">maybe-new-max</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">current-max</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">&gt; </span><span class="RktPn">(</span><span class="RktSym">for/max</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">3.14159</span><span class="hspace">&nbsp;</span><span class="RktVal">2.71828</span><span class="hspace">&nbsp;</span><span class="RktVal">1.61803</span><span class="RktVal">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">s</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal"><span class="nobreak">-1</span></span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVal">1</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVal">1</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktSym">s</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">2.71828</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.11.0.1 of package <span class="stt">base</span>: Added the <span class="RktPn">#:result</span> form.</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/private/base..rkt)._for*/fold/derived))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/fold/derived</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">orig-datum</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">maybe-result</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%29%29" class="RktStxLink" data-pltdoc="x">for*/fold</a></span>, but the extra <span class="RktVar">orig-datum</span> is used as the source for all syntax errors.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-syntax%29%29" class="RktStxLink" data-pltdoc="x">for-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktSym">syntax/for-body</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">syntax/parse/define</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Defining_Simple_Macros.html%23%2528form._%2528%2528lib._syntax%252Fparse%252Fdefine..rkt%2529._define-syntax-parse-rule%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-syntax-parse-rule</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">for*/digits</span><span class="hspace">&nbsp;</span><span class="RktSym">clauses</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktSym">original</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">#:with</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Parsing_for_Bodies.html%23%2528def._%2528%2528lib._syntax%252Ffor-body..rkt%2529._split-for-body%2529%2529&amp;version=8.6" class="RktValLink Sq" data-pltdoc="x">split-for-body</a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=stxparse-specifying.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._this-syntax%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">this-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktVar">body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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="hspace">&nbsp;</span><span class="RktSym">tail-expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for*/fold/derived</a></span><span class="hspace">&nbsp;</span><span class="RktSym">original</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktVal">0</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">[</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktPn">#:result</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">clauses</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktSym">pre-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</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">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">post-body</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2A%29%29" class="RktValLink" data-pltdoc="x">*</a></span><span class="hspace">&nbsp;</span><span class="RktSym">k</span><span class="hspace">&nbsp;</span><span class="RktVal">10</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">&gt; </span><span class="RktPn">(</span><span class="RktSym">for*/digits</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">ds</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">8</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="hspace">&nbsp;</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="RktVal">)</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">d</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktSym">ds</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">d</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktErr">eval:10:0: for*/digits: bad sequence binding clause</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace">&nbsp;&nbsp;</span><span class="RktErr">at: ds</span></p></td></tr><tr><td><p><span class="RktErr"></span><span class="hspace">&nbsp;&nbsp;</span><span class="RktErr">in: (for*/digits (ds (in-list (quote ((8 3) (1 1))))) (d</span></p></td></tr><tr><td><p><span class="RktErr">(in-list ds)) d)</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym">for*/digits</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">ds</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">(</span><span class="RktVal">8</span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktVal">)</span><span class="hspace">&nbsp;</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace">&nbsp;</span><span class="RktVal">1</span><span class="RktVal">)</span><span class="RktVal">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">d</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-list%29%29" class="RktValLink" data-pltdoc="x">in-list</a></span><span class="hspace">&nbsp;</span><span class="RktSym">ds</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktSym">d</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">1138</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Changed in version 6.11.0.1 of package <span class="stt">base</span>: Added the <span class="RktPn">#:result</span> form.</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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for/foldr/derived))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/foldr/derived</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">orig-datum</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">accum-option</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._for*/foldr/derived))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%2Fderived%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/foldr/derived</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">orig-datum</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">accum-id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">accum-option</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">body-or-break</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="hspace">&nbsp;</span><span class="RktVar">body</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for/foldr</a></span> and <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffoldr%29%29" class="RktStxLink" data-pltdoc="x">for*/foldr</a></span>, but the extra
<span class="RktVar">orig-datum</span> is used as the source for all syntax errors as in
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for/fold/derived</a></span> and <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2A%2Ffold%2Fderived%29%29" class="RktStxLink" data-pltdoc="x">for*/fold/derived</a></span>.</div></p><p class="SHistory">Added in version 7.3.0.3 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>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._define-sequence-syntax))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-sequence-syntax%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-sequence-syntax</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">id</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">expr-transform-expr</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">clause-transform-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><blockquote class="SubFlow"><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace">&nbsp;&nbsp;</span></td><td><span class="RktVar">expr-transform-expr</span></td><td><span class="hspace">&nbsp;</span></td><td>:</td><td><span class="hspace">&nbsp;</span></td><td><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">&nbsp;</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">-&gt;</span></a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="stxops.html#%28def._%28%28lib._racket%2Fprivate%2Fstx..rkt%29._identifier~3f%29%29" class="RktValLink" data-pltdoc="x">identifier?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span><span class="hspace">&nbsp;</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">-&gt;</span></a></span><span class="RktPn"> .</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table><table cellspacing="0" cellpadding="0" class="argcontract"><tr><td><span class="hspace">&nbsp;&nbsp;</span></td><td><span class="RktVar">clause-transform-expr</span></td><td><span class="hspace">&nbsp;</span></td><td>:</td><td><span class="hspace">&nbsp;</span></td><td><span class="RktPn">(</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span><span class="hspace">&nbsp;</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">-&gt;</span></a></span><span class="RktPn"> .</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Defines <span class="RktVar">id</span> as syntax. An <span class="RktPn">(</span><span class="RktVar">id</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">rest</span><span class="RktPn">)</span> form is
treated specially when used to generate a sequence in a
<span class="RktVar">for-clause</span> of <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> (or one of its variants). In that
case, the procedure result of <span class="RktVar">clause-transform-expr</span> is called
to transform the clause.</div></p><p>When <span class="RktVar">id</span> is used in any other expression position, the result
of <span class="RktVar">expr-transform-expr</span> is used. If it is a procedure of zero
arguments, then the result must be an identifier <span class="RktVar">other-id</span>,
and any use of <span class="RktVar">id</span> is converted to a use of
<span class="RktVar">other-id</span>. Otherwise, <span class="RktVar">expr-transform-expr</span> must
produce a procedure (of one argument) that is used as a macro
transformer.</p><p>When the <span class="RktVar">clause-transform-expr</span> transformer is used, it is
given a <span class="RktVar">for-clause</span> as an argument, where the clause&rsquo;s form is
normalized so that the left-hand side is a parenthesized sequence of
identifiers. The right-hand side is of the form <span class="RktPn">(</span><span class="RktVar">id</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">rest</span><span class="RktPn">)</span>.
The result can be either <span class="RktVal">#f</span>, to indicate that the forms
should not be treated specially (perhaps because the number of bound
identifiers is inconsistent with the <span class="RktPn">(</span><span class="RktVar">id</span><span class="stt"> </span><span class="RktPn">. </span><span class="RktVar">rest</span><span class="RktPn">)</span> form), or a
new <span class="RktVar">for-clause</span> to replace the given one. The new clause might
use <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span>. To protect identifiers in the result of
<span class="RktVar">clause-transform-expr</span>, use <span class="RktSym"><a href="for.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-clause-syntax-protect%29%29" class="RktValLink" data-pltdoc="x">for-clause-syntax-protect</a></span>
instead of <span class="RktSym"><a href="stxcerts.html#%28def._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-protect%29%29" class="RktValLink" data-pltdoc="x">syntax-protect</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">&gt; </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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">check-nat</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._unless%29%29" class="RktStxLink" data-pltdoc="x">unless</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</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">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._raise-argument-error%29%29" class="RktValLink" data-pltdoc="x">raise-argument-error</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">in-digits</span><span class="hspace">&nbsp;</span><span class="RktVal">"exact-nonnegative-integer?"</span><span class="hspace">&nbsp;</span><span class="RktSym">n</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-sequence-syntax%29%29" class="RktStxLink" data-pltdoc="x">define-sequence-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktSym">in-digits</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktRdr">#'</span><span class="RktSym">in-digits/proc</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-case%29%29" class="RktStxLink" data-pltdoc="x">syntax-case</a></span><span class="hspace">&nbsp;</span><span class="RktSym">stx</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">d</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</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="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Library_Syntax_Classes_and_Literal_Sets.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._nat%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">nat</a></span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktRdr">#'</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">d</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">n</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=syntax&amp;rel=Library_Syntax_Classes_and_Literal_Sets.html%23%2528form._%2528%2528lib._syntax%252Fparse..rkt%2529._nat%2529%2529&amp;version=8.6" class="RktStxLink Sq" data-pltdoc="x">nat</a></span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">check-nat</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._not%29%29" class="RktValLink" data-pltdoc="x">not</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._zero~3f%29%29" class="RktValLink" data-pltdoc="x">zero?</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">j</span><span class="hspace">&nbsp;</span><span class="RktSym">d</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._quotient%2Fremainder%29%29" class="RktValLink" data-pltdoc="x">quotient/remainder</a></span><span class="hspace">&nbsp;</span><span class="RktSym">i</span><span class="hspace">&nbsp;</span><span class="RktVal">10</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVal">#t</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVal">#t</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">j</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</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="hspace">&nbsp;</span><span class="RktVal">#f</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">&gt; </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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">in-digits/proc</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">d</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">in-digits</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">d</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">d</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">in-digits</span><span class="hspace">&nbsp;</span><span class="RktVal">1138</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktSym">d</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(8 3 1 1)</span></p></td></tr><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Fprivate%2Fmap..rkt%29._map%29%29" class="RktValLink" data-pltdoc="x">map</a></span><span class="hspace">&nbsp;</span><span class="RktSym">in-digits</span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktVal">137</span><span class="hspace">&nbsp;</span><span class="RktVal">216</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'((7 3 1) (6 1 2))</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><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/private/base..rkt)._~3ado-in))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">:do-in</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">outer-id</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">outer-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">outer-check</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">loop-id</span><span class="hspace">&nbsp;</span><span class="RktVar">loop-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">pos-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">inner-id</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktVar">inner-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">pre-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">post-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktVar">loop-arg</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A form that can only be used as a <span class="RktVar">seq-expr</span> in a
<span class="RktVar">for-clause</span> of <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> (or one of its variants).</div></p><p>Within a <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span>, the pieces of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span> form are
spliced into the iteration essentially as follows:</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._let-values%29%29" class="RktStxLink" data-pltdoc="x">let-values</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">outer-id</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktVar">outer-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">outer-check</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktSym">loop</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">loop-id</span><span class="hspace">&nbsp;</span><span class="RktVar">loop-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace">&nbsp;</span><span class="RktVar">pos-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="let.html#%28form._%28%28quote._~23~25kernel%29._let-values%29%29" class="RktStxLink" data-pltdoc="x">let-values</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">inner-id</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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><span class="hspace">&nbsp;</span><span class="RktVar">inner-expr</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace">&nbsp;</span><span class="RktVar">pre-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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">&nbsp;</span><span class="RktVar">body-bindings</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace">&nbsp;</span><span class="RktVar">post-guard</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">loop</span><span class="hspace">&nbsp;</span><span class="RktVar">loop-arg</span><span class="hspace">&nbsp;</span><span class="RktMeta"><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></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">done-expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">done-expr</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktVar">done-expr</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>where <span class="RktVar">body-bindings</span> and <span class="RktVar">done-expr</span> are from the
context of the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span> use. The identifiers bound by the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> clause are typically part of the <span class="RktPn">(</span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktVar">inner-id</span><span class="stt"> </span><span class="RktMeta"><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><span class="stt"> </span><span class="RktVar">inner-expr</span><span class="RktPn">]</span><span class="stt"> </span><span class="RktMeta"><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> section.</p><p>Beware that <span class="RktVar">body-bindings</span> and <span class="RktVar">done-expr</span> can
contain arbitrary expressions, potentially including <span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span> on
<span class="RktVar">outer-id</span> or <span class="RktVar">inner-id</span> identifiers if they are visible
in the original <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form, so beware of depending on such
identifiers in <span class="RktVar">post-guard</span> and <span class="RktVar">loop-arg</span>.</p><p>The actual <span class="RktSym">loop</span> binding and call has additional loop
arguments to support iterations in parallel with the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span>
form, and the other pieces are similarly accompanied by pieces from
parallel iterations.</p><p>For an example of <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~3ado-in%29%29" class="RktStxLink" data-pltdoc="x">:do-in</a></span>, see <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-sequence-syntax%29%29" class="RktStxLink" data-pltdoc="x">define-sequence-syntax</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/private/base..rkt)._for-clause-syntax-protect))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-clause-syntax-protect%29%29" class="RktValDef RktValLink" data-pltdoc="x">for-clause-syntax-protect</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">stx</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span>&rarr;<span class="hspace">&nbsp;</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></p></blockquote></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">stx</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Provided <span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for-syntax%29%29" class="RktStxLink" data-pltdoc="x">for-syntax</a></span>: Like <span class="RktSym"><a href="stxcerts.html#%28def._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-protect%29%29" class="RktValLink" data-pltdoc="x">syntax-protect</a></span>, just
returns its argument.</div></p><p class="SHistory">Changed in version 8.2.0.4 of package <span class="stt">base</span>: Changed to just return <span class="RktVar">stx</span> instead
of returning &ldquo;armed&rdquo; syntax.</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/private/base..rkt)._define-splicing-for-clause-syntax))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-splicing-for-clause-syntax%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">define-splicing-for-clause-syntax</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktVar">proc-expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Binds <span class="RktVar">id</span> for reference via a <span class="RktPn">#:splicing</span> clause in a
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form. The <span class="RktVar">proc-expr</span> expression is evaluated in
<a href="syntax-model.html#%28tech._phase._level%29" class="techoutside" data-pltdoc="x"><span class="techinside">phase level</span></a> 1, and it must produce a procedure that accepts a
syntax object and returns a syntax object.</div></p><p>The procedure&rsquo;s input is a syntax object that appears after
<span class="RktPn">#:splicing</span>. The result syntax object must be a parenthesized
sequence of forms, and the forms are spliced in place of the
<span class="RktPn">#:splicing</span> clause in the enclosing <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span> form.</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">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-splicing-for-clause-syntax%29%29" class="RktStxLink" data-pltdoc="x">define-splicing-for-clause-syntax</a></span><span class="hspace">&nbsp;</span><span class="RktSym">cross3</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</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">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._syntax-case%29%29" class="RktStxLink" data-pltdoc="x">syntax-case</a></span><span class="hspace">&nbsp;</span><span class="RktSym">stx</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktPn">(</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="hspace">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktSym">m</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span><span class="RktRdr">#'</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-range%29%29" class="RktValLink" data-pltdoc="x">in-range</a></span><span class="hspace">&nbsp;</span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">#:when</span><span class="hspace">&nbsp;</span><span class="RktVal">#t</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">[</span><span class="RktSym">m</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="sequences.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-range%29%29" class="RktValLink" data-pltdoc="x">in-range</a></span><span class="hspace">&nbsp;</span><span class="RktVal">3</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><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">&gt; </span><span class="RktPn">(</span><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%29%29" class="RktStxLink" data-pltdoc="x">for</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">#:splice</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">cross3</span><span class="hspace">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktSym">m</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._println%29%29" class="RktValLink" data-pltdoc="x">println</a></span><span class="hspace">&nbsp;</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">&nbsp;</span><span class="RktSym">n</span><span class="hspace">&nbsp;</span><span class="RktSym">m</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"><tr><td><p><span class="RktOut">'(0 0)</span></p></td></tr><tr><td><p><span class="RktOut">'(0 1)</span></p></td></tr><tr><td><p><span class="RktOut">'(0 2)</span></p></td></tr><tr><td><p><span class="RktOut">'(1 0)</span></p></td></tr><tr><td><p><span class="RktOut">'(1 1)</span></p></td></tr><tr><td><p><span class="RktOut">'(1 2)</span></p></td></tr><tr><td><p><span class="RktOut">'(2 0)</span></p></td></tr><tr><td><p><span class="RktOut">'(2 1)</span></p></td></tr><tr><td><p><span class="RktOut">'(2 2)</span></p></td></tr></table></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 8.4.0.3 of package <span class="stt">base</span>.</p><h5 x-source-module="(lib &quot;scribblings/reference/reference.scrbl&quot;)" x-source-pkg="racket-doc" x-part-tag="&quot;Do_Loops&quot;">3.18.3<tt>&nbsp;</tt><a name="(part._.Do_.Loops)"></a>Do Loops</h5><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/private/more-scheme..rkt)._do))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._do%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">do</a></span></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktVar">id</span><span class="hspace">&nbsp;</span><span class="RktVar">init-expr</span><span class="hspace">&nbsp;</span><span class="RktVar">step-expr-maybe</span><span class="RktPn">]</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktVar">stop?-expr</span><span class="hspace">&nbsp;</span><span class="RktVar">finish-expr</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">expr</span><span class="hspace">&nbsp;</span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt">&nbsp;</span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">step-expr-maybe</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt">&nbsp;</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">&nbsp;</span></td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt">&nbsp;</span></td><td align="left" valign="baseline"><span class="RktVar">step-expr</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Iteratively evaluates the <span class="RktVar">expr</span>s for as long as
<span class="RktVar">stop?-expr</span> returns <span class="RktVal">#f</span>.</div></p><p>To initialize the loop, the <span class="RktVar">init-expr</span>s are evaluated in order
and bound to the corresponding <span class="RktVar">id</span>s. The <span class="RktVar">id</span>s are
bound in all expressions within the form other than the
<span class="RktVar">init-expr</span>s.</p><p>After the <span class="RktVar">id</span>s have been bound, the <span class="RktVar">stop?-expr</span> is
evaluated. If it produces <span class="RktVal">#f</span>, each <span class="RktVar">expr</span> is evaluated
for its side-effect. The <span class="RktVar">id</span>s are then effectively updated
with the values of the <span class="RktVar">step-expr</span>s, where the default
<span class="RktVar">step-expr</span> for <span class="RktVar">id</span> is just <span class="RktVar">id</span>; more
precisely, iteration continues with fresh locations for the
<span class="RktVar">id</span>s that are initialized with the values of the corresponding
<span class="RktVar">step-expr</span>s.</p><p>When <span class="RktVar">stop?-expr</span> produces a true value, then the
<span class="RktVar">finish-expr</span>s are evaluated in order, and the last one is
evaluated in tail position to produce the overall value for the
<span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._do%29%29" class="RktStxLink" data-pltdoc="x">do</a></span> form. If no <span class="RktVar">finish-expr</span> is provided, the value of
the <span class="RktSym"><a href="for.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._do%29%29" class="RktStxLink" data-pltdoc="x">do</a></span> form is <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&amp;rel=void_undefined.html&amp;version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#&lt;void&gt;</span></span></a>.</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, &quot;8.6&quot;, &quot;../&quot;);"/></form>&nbsp;&nbsp;<a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;8.6&quot;);">top</a><span class="tocsettoggle">&nbsp;&nbsp;<a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright">&nbsp;&nbsp;<a href="set_.html" title="backward to &quot;3.17 Assignment: set! and set!-values&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="syntax.html" title="up to &quot;3 Syntactic Forms&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="wcm.html" title="forward to &quot;3.19 Continuation Marks: with-continuation-mark&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div></div></div><div id="contextindicator">&nbsp;</div></body></html>
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