104 lines
99 KiB
HTML
104 lines
99 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>4.16.2 Streams</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewselflink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" class="tocview
|
||
|
|
functional iteration via <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span> and
|
||
|
|
<span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValLink" data-pltdoc="x">stream-rest</a></span>. The <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> form constructs a lazy
|
||
|
|
stream, but plain lists can be used as streams, and functions such as
|
||
|
|
<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> and <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> also create streams.</p><p><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left"><span class="hspace"> </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="stt"> </span><a href="streams.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/stream</span></a><span class="RktPn">)</span></td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <a href="https://pkgs.racket-lang.org/package/base" title="Install this package using `raco pkg install base`"><span class="stt">base</span></a></span></td></tr></table></div><div class="SIntrapara">The bindings documented in this section are provided by the <a href="streams.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/stream</span></a> and <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket</span></a> libraries, but not <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/base</span></a>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream~3f))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">v</span> can be used as a <a href="streams.html#%28tech._stream%29" class="techoutside" data-pltdoc="x"><span class="techinside">stream</span></a>,
|
||
|
|
<span class="RktVal">#f</span> otherwise.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-empty~3f))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-empty~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-empty?</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">s</span> has no elements, <span class="RktVal">#f</span>
|
||
|
|
otherwise.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-first))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-first</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-empty~3f%29%29" class="RktValLink" data-pltdoc="x">stream-empty?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the value(s) of the first element in <span class="RktVar">s</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-rest))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-rest</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt
|
||
|
|
element.</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/stream..rkt)._stream-cons))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-cons%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-cons</a></span></span><span class="hspace"> </span><span class="RktVar">first-expr</span><span class="hspace"> </span><span class="RktVar">rest-expr</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-cons%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-cons</a></span><span class="hspace"> </span><span class="RktPn">#:eager</span><span class="hspace"> </span><span class="RktVar">first-expr</span><span class="hspace"> </span><span class="RktVar">rest-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-cons%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-cons</a></span><span class="hspace"> </span><span class="RktVar">first-expr</span><span class="hspace"> </span><span class="RktPn">#:eager</span><span class="hspace"> </span><span class="RktVar">rest-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-cons%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-cons</a></span><span class="hspace"> </span><span class="RktPn">#:eager</span><span class="hspace"> </span><span class="RktVar">first-expr</span><span class="hspace"> </span><span class="RktPn">#:eager</span><span class="hspace"> </span><span class="RktVar">rest-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a stream whose first element is determined by
|
||
|
|
<span class="RktVar">first-expr</span> and whose rest is determined by
|
||
|
|
<span class="RktVar">rest-expr</span>.</div></p><p>If <span class="RktVar">first-expr</span> is not preceded by <span class="RktPn">#:eager</span>, then
|
||
|
|
<span class="RktVar">first-expr</span> is not evaluated immediately. Instead,
|
||
|
|
<span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span> on the result stream forces the evaluation of
|
||
|
|
<span class="RktVar">first-expr</span> (once) to produce the first element of the
|
||
|
|
stream. If evaluating <span class="RktVar">first-expr</span> raises an exception or
|
||
|
|
tries to force itself, then an <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> exception is raised, and
|
||
|
|
future attempts to force evaluation will trigger another exception.</p><p>If <span class="RktVar">rest-expr</span> is not preceded by <span class="RktPn">#:eager</span>, then
|
||
|
|
<span class="RktVar">rest-expr</span> is not evaluated immediately. Instead,
|
||
|
|
<span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValLink" data-pltdoc="x">stream-rest</a></span> on the result stream produces another stream
|
||
|
|
that is like the one produced by <span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-lazy%29%29" class="RktStxLink" data-pltdoc="x">stream-lazy</a></span><span class="stt"> </span><span class="RktVar">rest-expr</span><span class="RktPn">)</span>.</p><p>The first element of the stream as produced by <span class="RktVar">first-expr</span>
|
||
|
|
must be a single value. The <span class="RktVar">rest-expr</span> must produce a stream
|
||
|
|
when it is evaluated, otherwise the <span class="RktSym"><a href="exns.html#%28def._%28%28quote._~23~25kernel%29._exn~3afail~3acontract~3f%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract?</a></span> exception is raised.</p><p class="SHistory">Changed in version 8.0.0.12 of package <span class="stt">base</span>: Added <span class="RktPn">#:eager</span> options.</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/stream..rkt)._stream-lazy))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-lazy%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-lazy</a></span></span><span class="hspace"> </span><span class="RktVar">stream-expr</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-lazy%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream-lazy</a></span><span class="hspace"> </span><span class="RktPn">#:who</span><span class="hspace"> </span><span class="RktVar">who-expr</span><span class="hspace"> </span><span class="RktVar">stream-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktPn">(</span><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="stt"> </span><span class="RktVar">stream-expr</span><span class="RktPn">)</span>, but the result is a stream
|
||
|
|
instead of a <a href="Delayed_Evaluation.html#%28tech._promise%29" class="techoutside" data-pltdoc="x"><span class="techinside">promise</span></a>, and <span class="RktVar">stream-expr</span> must produce a
|
||
|
|
stream when it is eventually forced. The stream produced by
|
||
|
|
<span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-lazy%29%29" class="RktStxLink" data-pltdoc="x">stream-lazy</a></span> has the same content as the stream produced by
|
||
|
|
<span class="RktVar">stream-expr</span>; that is, operations like <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span>
|
||
|
|
on the result stream will force <span class="RktVar">stream-expr</span> and retry on its
|
||
|
|
result.</div></p><p>If evaluating <span class="RktVar">stream-expr</span> raises an exception or tries to
|
||
|
|
force itself, then an <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3acontract%29%29" class="RktValLink" data-pltdoc="x">exn:fail:contract</a></span> exception is raised, and future
|
||
|
|
attempts to force evaluation will trigger another exception.</p><p>If <span class="RktVar">who-expr</span> is provided, it is evaluated when constructing
|
||
|
|
the delayed stream. If <span class="RktVar">stream-expr</span> later produces a value
|
||
|
|
that is not a stream, and if <span class="RktVar">who-expr</span> produced a symbol
|
||
|
|
value, then the symbol is used for the error message.</p><p class="SHistory">Added in version 8.0.0.12 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-force))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-force%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-force</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Forces the evaluation of a delayed stream from <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream-lazy%29%29" class="RktStxLink" data-pltdoc="x">stream-lazy</a></span>,
|
||
|
|
from the <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValLink" data-pltdoc="x">stream-rest</a></span> of a <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>, etc.,
|
||
|
|
returning the forced stream. If <span class="RktVar">s</span> is not a delayed stream,
|
||
|
|
then <span class="RktVar">s</span> is returned.</div></p><p>Normally, <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-force%29%29" class="RktValLink" data-pltdoc="x">stream-force</a></span> is not needed, because operations
|
||
|
|
like <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span>, <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValLink" data-pltdoc="x">stream-rest</a></span>, and
|
||
|
|
<span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-empty~3f%29%29" class="RktValLink" data-pltdoc="x">stream-empty?</a></span> force a delayed stream as needed. In rare
|
||
|
|
cases, <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-force%29%29" class="RktValLink" data-pltdoc="x">stream-force</a></span> can be useful to reveal the underlying
|
||
|
|
implementation of a stream (e.g., a stream that is an instance of a
|
||
|
|
structure type that has the <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._prop~3astream%29%29" class="RktValLink" data-pltdoc="x">prop:stream</a></span> property).</p><p class="SHistory">Added in version 8.0.0.12 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/stream..rkt)._stream))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream</a></span></span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A shorthand for nested <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>es ending with
|
||
|
|
<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>. As a match pattern, <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxLink" data-pltdoc="x">stream</a></span>
|
||
|
|
matches a stream with as many elements as <span class="RktVar">e</span>s,
|
||
|
|
and each element must match the corresponding <span class="RktVar">e</span> pattern.</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/stream..rkt)._stream*))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%2A%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">stream*</a></span></span><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">tail</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A shorthand for nested <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>es, but the <span class="RktVar">tail</span>
|
||
|
|
must produce a stream when it is forced, and that stream is used as the rest of the stream instead of
|
||
|
|
<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>. Similar to <span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list%2A%29%29" class="RktValLink" data-pltdoc="x">list*</a></span> but for streams.
|
||
|
|
As a match pattern, <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%2A%29%29" class="RktStxLink" data-pltdoc="x">stream*</a></span> is similar to a <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxLink" data-pltdoc="x">stream</a></span> pattern,
|
||
|
|
but the <span class="RktVar">tail</span> pattern matches the “rest” of the stream after the last <span class="RktVar">e</span>.</div></p><p class="SHistory">Added in version 6.3 of package <span class="stt">base</span>.<br/>Changed in version 8.0.0.12: Changed to delay <span class="RktSym">rest-expr</span> even
|
||
|
|
if zero <span class="RktSym">expr</span>s are provided.</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/stream..rkt)._in-stream))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._in-stream%29%29" class="RktValDef RktValLink" data-pltdoc="x">in-stream</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><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></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a sequence that is equivalent to <span class="RktVar">s</span>.
|
||
|
|
</div><div class="SIntrapara">An <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._in-stream%29%29" class="RktValLink" data-pltdoc="x">in-stream</a></span> application can provide better performance for streams iteration when it appears directly 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> clause.</div><div class="SIntrapara">See <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> for information on the reachability of stream elements
|
||
|
|
during an iteration.</div></p><p class="SHistory">Changed in version 6.7.0.4 of package <span class="stt">base</span>: Improved element-reachability guarantee for streams in <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><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/stream..rkt)._empty-stream))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._empty-stream%29%29" class="RktValDef RktValLink" data-pltdoc="x">empty-stream</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A stream with no elements.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-~3elist))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-~3elist%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream->list</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="pairs.html#%28def._%28%28quote._~23~25kernel%29._list~3f%29%29" class="RktValLink" data-pltdoc="x">list?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a list whose elements are the elements of <span class="RktVar">s</span>, each
|
||
|
|
of which must be a single value. If <span class="RktVar">s</span> is infinite, this
|
||
|
|
function does not terminate.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-length))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-length%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-length</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the number of elements of <span class="RktVar">s</span>. If <span class="RktVar">s</span> is
|
||
|
|
infinite, this function does not terminate.</div></p><p>In the case of lazy streams, this function forces evaluation only of
|
||
|
|
the sub-streams, and not the stream’s elements.</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/stream..rkt)._stream-ref))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-ref%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-ref</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the <span class="RktVar">i</span>th element of <span class="RktVar">s</span> (which may be
|
||
|
|
multiple values).</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-tail))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-tail%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-tail</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream equivalent to <span class="RktVar">s</span>, except that the first
|
||
|
|
<span class="RktVar">i</span> elements are omitted.</div></p><p>In case extracting elements from <span class="RktVar">s</span> involves a side effect,
|
||
|
|
they will not be extracted until the first element is extracted from
|
||
|
|
the resulting stream.</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/stream..rkt)._stream-take))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-take%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-take</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">i</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream of the first <span class="RktVar">i</span> elements of <span class="RktVar">s</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-append))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-append%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-append</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream that contains all elements of each stream in the
|
||
|
|
order they appear in the original streams. The new stream is
|
||
|
|
constructed lazily, while the last given stream is used in the tail
|
||
|
|
of the result.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-map))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-map%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-map</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure~3f%29%29" class="RktValLink" data-pltdoc="x">procedure?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream that contains <span class="RktVar">f</span> applied to each element of
|
||
|
|
<span class="RktVar">s</span>. The new stream is constructed lazily.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-andmap))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-andmap%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-andmap</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">f</span> returns a true result on every
|
||
|
|
element of <span class="RktVar">s</span>. If <span class="RktVar">s</span> is infinite and <span class="RktVar">f</span>
|
||
|
|
never returns a false result, this function does not terminate.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-ormap))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-ormap%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-ormap</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">f</span> returns a true result on some
|
||
|
|
element of <span class="RktVar">s</span>. If <span class="RktVar">s</span> is infinite and <span class="RktVar">f</span>
|
||
|
|
never returns a true result, this function does not terminate.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-for-each))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-for-each%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-for-each</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Applies <span class="RktVar">f</span> to each element of <span class="RktVar">s</span>. If <span class="RktVar">s</span> is
|
||
|
|
infinite, this function does not terminate.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-fold))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-fold%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-fold</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </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"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">i</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Folds <span class="RktVar">f</span> over each element of <span class="RktVar">s</span> with <span class="RktVar">i</span> as
|
||
|
|
the initial accumulator. If <span class="RktVar">s</span> is infinite, this function
|
||
|
|
does not terminate. The <span class="RktVar">f</span> function takes the accumulator as
|
||
|
|
its first argument and the next stream element as its second.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-count))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-count%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-count</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure~3f%29%29" class="RktValLink" data-pltdoc="x">procedure?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the number of elements in <span class="RktVar">s</span> for which <span class="RktVar">f</span>
|
||
|
|
returns a true result. If <span class="RktVar">s</span> is infinite, this function
|
||
|
|
does not terminate.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-filter))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-filter%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-filter</a></span></span><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">f</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream whose elements are the elements of <span class="RktVar">s</span> for
|
||
|
|
which <span class="RktVar">f</span> returns a true result. Although the new stream is
|
||
|
|
constructed lazily, if <span class="RktVar">s</span> has an infinite number of elements
|
||
|
|
where <span class="RktVar">f</span> returns a false result in between two elements
|
||
|
|
where <span class="RktVar">f</span> returns a true result, then operations on this
|
||
|
|
stream will not terminate during the infinite sub-stream.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream-add-between))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-add-between%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream-add-between</a></span></span><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span><span class="RktVar">e</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">s</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream~3f%29%29" class="RktValLink" data-pltdoc="x">stream?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">e</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stream whose elements are the elements of <span class="RktVar">s</span>, but
|
||
|
|
with <span class="RktVar">e</span> between each pair of elements in <span class="RktVar">s</span>. The
|
||
|
|
new stream is constructed lazily.</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/stream..rkt)._for/stream))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2Fstream%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for/stream</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body-or-break</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </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/stream..rkt)._for*/stream))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2A%2Fstream%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">for*/stream</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">for-clause</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">body-or-break</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </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%2Flist%29%29" class="RktStxLink" data-pltdoc="x">for/list</a></span> and <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>, respectively, but the
|
||
|
|
results are lazily collected into a <a href="streams.html#%28tech._stream%29" class="techoutside" data-pltdoc="x"><span class="techinside">stream</span></a> instead of a list.</div></p><p>Unlike most <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, these forms are evaluated lazily, so each
|
||
|
|
<span class="RktVar">body</span> will not be evaluated until the resulting stream is forced. This
|
||
|
|
allows <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> and <span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2A%2Fstream%29%29" class="RktStxLink" data-pltdoc="x">for*/stream</a></span> to iterate over infinite
|
||
|
|
sequences, unlike their finite counterparts.</p><p>Please note that these forms do not support returning <a href="eval-model.html#%28tech._multiple._value%29" class="techoutside" data-pltdoc="x"><span class="techinside">multiple values</span></a>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._for%2Fstream%29%29" class="RktStxLink" data-pltdoc="x">for/stream</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace"> </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"> </span><span class="RktSym">i</span><span class="hspace"> </span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<stream></span></p></td></tr><tr><td><span class="stt">> </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->list</a></span><span class="hspace"> </span><span class="RktPn">(</span><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><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace"> </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"> </span><span class="RktSym">i</span><span class="hspace"> </span><span class="RktSym">i</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(1 4 9)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-ref%29%29" class="RktValLink" data-pltdoc="x">stream-ref</a></span><span class="hspace"> </span><span class="RktPn">(</span><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><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">i</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span cl
|
||
|
|
<a href="struct-generics.html#%28tech._generic._interface%29" class="techoutside" data-pltdoc="x"><span class="techinside">generic interface</span></a> (see <a href="struct-generics.html" data-pltdoc="x">Generic Interfaces</a>) for
|
||
|
|
streams.</div></p><p>To supply method implementations, the <span class="RktPn">#:methods</span> keyword
|
||
|
|
should be used in a structure type definition. The following three
|
||
|
|
methods should be implemented:</p><ul><li><p><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-empty~3f%29%29" class="RktValLink" data-pltdoc="x">stream-empty?</a></span> : accepts one argument</p></li><li><p><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span> : accepts one argument</p></li><li><p><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-rest%29%29" class="RktValLink" data-pltdoc="x">stream-rest</a></span> : accepts one argument</p></li></ul><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">list-stream</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">v</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:methods</span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._gen~3astream%29%29" class="RktValLink" data-pltdoc="x">gen:stream</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </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"> </span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-empty~3f%29%29" class="RktValLink" data-pltdoc="x">stream-empty?</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxLink" data-pltdoc="x">stream</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._empty~3f%29%29" class="RktValLink" data-pltdoc="x">empty?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">list-stream-v</span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxLink" data-pltdoc="x">stream</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream-first%29%29" class="RktValLink" data-pltdoc="x">stream-first</a></span><span class="hspace"> </span><span class="RktSym"><a href="streams.html#%28form._%28%28lib._racket%2Fstream..rkt%29._stream%29%29" class="RktStxLink" data-pltdoc="x">stream</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="pairs.html#%28def._%28%28lib._racket%2Flist..rkt%29._first%29%29" class="RktValLink" data-pltdoc="x">first</a></span><span clas
|
||
|
|
extensions to the stream API. Using the <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._prop~3astream%29%29" class="RktValLink" data-pltdoc="x">prop:stream</a></span> property
|
||
|
|
is discouraged; use the <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._gen~3astream%29%29" class="RktValLink" data-pltdoc="x">gen:stream</a></span> <a href="struct-generics.html#%28tech._generic._interface%29" class="techoutside" data-pltdoc="x"><span class="techinside">generic interface</span></a>
|
||
|
|
instead. Accepts a vector of three procedures taking the same arguments
|
||
|
|
as the methods in <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._gen~3astream%29%29" class="RktValLink" data-pltdoc="x">gen:stream</a></span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/stream..rkt)._stream/c))"></a><span title="Provided from: racket/stream, racket | Package: base"><span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">stream/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes streams. All elements of the stream must match
|
||
|
|
<span class="RktVar">c</span>.</div></p><p>If the <span class="RktVar">c</span> argument is a flat contract or a chaperone contract, then the
|
||
|
|
result will be a chaperone contract. Otherwise, the result will be an
|
||
|
|
impersonator contract.</p><p>When an <span class="RktSym"><a href="streams.html#%28def._%28%28lib._racket%2Fstream..rkt%29._stream%2Fc%29%29" class="RktValLink" data-pltdoc="x">stream/c</a></span> contract is applied to a stream, the result is not
|
||
|
|
<span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input. The result will be either a <a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or
|
||
|
|
<a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the input depending on the type of contract.</p><p>Contracts on streams are evaluated lazily by necessity (since streams may be
|
||
|
|
infinite). Contract violations will not be raised until the value in violation
|
||
|
|
is retrieved from the stream. As an exception to this rule, streams that are
|
||
|
|
lists are checked immediately, as if <span class="RktVar">c</span> had been used with
|
||
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span>.</p><p>If a contract is applied to a stream, and that stream is subsequently used as
|
||
|
|
the tail of another stream (as the second parameter to <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>),
|
||
|
|
the new elements will not be checked with the contract, but the tail’s elements
|
||
|
|
will still be enforced.</p><p class="SHistory">Added in version 6.1.1.8 of package <span class="stt">base</span>.</p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="sequences.html" title="backward to "4.16.1 Sequences"" data-pltdoc="x">← prev</a> <a href="sequences_streams.html" title="up to "4.16 Sequences and Streams"" data-pltdoc="x">up</a> <a href="Generators.html" title="forward to "4.16.3 Generators"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
|