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185 lines
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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>13.4 Reading</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,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="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="tocviewselflink" 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><
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<span class="RktVar">in</span> has a handler associated to it via
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._port-read-handler%29%29" class="RktValLink" data-pltdoc="x">port-read-handler</a></span>, then the handler is called. Otherwise, the
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default reader is used, as parameterized by the
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-readtable%29%29" class="RktValLink" data-pltdoc="x">current-readtable</a></span> parameter, as well as many other
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parameters.</div></p><p>See <a href="reader.html" data-pltdoc="x">The Reader</a> for information on the default reader and
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<a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a> for the protocol of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</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._((quote._~23~25kernel)._read-syntax))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-syntax</a></span></span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">source-name</span><span class="hspace"> </span><span class="RktVar">in</span><span class="RktOpt">]</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="stxops.html#%28def._%28%28quote._~23~25kernel%29._syntax~3f%29%29" class="RktValLink" data-pltdoc="x">syntax?</a></span><span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._eof-object~3f%29%29" class="RktValLink" data-pltdoc="x">eof-object?</a></span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">source-name</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._object-name%29%29" class="RktValLink" data-pltdoc="x">object-name</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-input-port%29%29" class="RktValLink" data-pltdoc="x">current-input-port</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-input-port%29%29" class="RktValLink" data-pltdoc="x">current-input-port</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>, but produces a <a href="syntax-model.html#%28tech._syntax._object%29" class="techoutside" data-pltdoc="x"><span class="techinside">syntax object</span></a> with
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source-location information. The <span class="RktVar">source-name</span> is used as the
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source field of the syntax object; it can be an arbitrary value, but
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it should generally be a path for the source file.</div></p><p>See <a href="reader.html" data-pltdoc="x">The Reader</a> for information on the default reader in
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> mode and <a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a> for
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the protocol of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span>.</p><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="finger.png" alt="+" width="24" height="24"/></span>See also <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=stx-obj.html&version=8.6" class="Sq" data-pltdoc="x">Syntax Objects</a> in <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=index.html&version=8.6" class="Sq" data-pltdoc="x">The Racket Guide</a>.</p></blockquote></blockquote></blockquote><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read/recursive))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValDef RktValLink" data-pltdoc="x">read/recursive</a></span></span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">in</span><span class="hspace"> </span><span class="RktVar">start</span><span class="hspace"> </span><span class="RktVar">readtable</span><span class="hspace"> </span><span class="RktVar">graph?</span><span class="RktOpt">]</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">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-input-port%29%29" class="RktValLink" data-pltdoc="x">current-input-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">start</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="characters.html#%28def._%28%28quote._~23~25kernel%29._char~3f%29%29" class="RktValLink" data-pltdoc="x">char?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">readtable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="readtables.html#%28def._%28%28quote._~23~25kernel%29._readtable~3f%29%29" class="RktValLink" data-pltdoc="x">readtable?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><
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extent of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span> within a reader-extension procedure (see
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<a href="reader-procs.html" data-pltdoc="x">Reader-Extension Procedures</a>). The main effect of using
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> instead of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span> is that
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graph-structure annotations (see <a href="reader.html#%28part._parse-graph%29" data-pltdoc="x">Reading Graph Structure</a>) in the
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nested read are considered part of the overall read, at least when the
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<span class="RktVar">graph?</span> argument is true; since the result is wrapped in a
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placeholder, however, it is not directly inspectable.</div></p><p>If <span class="RktVar">start</span> is provided and not <span class="RktVal">#f</span>, it is effectively
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prefixed to the beginning of <span class="RktVar">in</span>’s stream for the read. (To
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prefix multiple characters, use <span class="RktSym"><a href="port-lib.html#%28def._%28%28lib._racket%2Fport..rkt%29._input-port-append%29%29" class="RktValLink" data-pltdoc="x">input-port-append</a></span>.)</p><p>The <span class="RktVar">readtable</span> argument is used for top-level parsing to
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satisfy the read request, including various delimiters of a built-in
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top-level form (such as parentheses and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">.</span><span class="hspace"></span></span> for reading a hash
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table); recursive parsing within the read (e.g., to
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read the elements of a list) instead uses the current readtable as
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determined by the <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-readtable%29%29" class="RktValLink" data-pltdoc="x">current-readtable</a></span> parameter. A reader
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macro might call <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> with a character and
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readtable to effectively invoke the readtable’s behavior for the
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character. If <span class="RktVar">readtable</span> is <span class="RktVal">#f</span>, the default
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readtable is used for top-level parsing.</p><p>When <span class="RktVar">graph?</span> is <span class="RktVal">#f</span>, graph structure annotations in
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the read datum are local to the datum.</p><p>When called within the dynamic extent of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>, the
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> procedure can produce a special-comment value
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(see <a href="special-comments.html" data-pltdoc="x">Special Comments</a>) when the input stream’s first
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non-whitespace content parses as a comment.</p><p>See <a href="readtables.html" data-pltdoc="x">Readtables</a> for an extended example that uses
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span>.</p><p class="SHistory">Changed in version 6.2 of package <span class="stt">base</span>: Adjusted use of <span class="RktVar">readtable</span> to
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more consistently apply to the delimiters of
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a built-in 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>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-syntax/recursive))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-syntax/recursive</a></span></span></td><td valign="top"><span class="hspace"> </span><span class="RktOpt">[</span></td><td valign="top"><span class="RktVar">source-name</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">in</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">start</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">readtable</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">graph?</span><span class="RktOpt">]</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">source-name</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="inspectors.html#%28def._%28%28quote._~23~25kernel%29._object-name%29%29" class="RktValLink" data-pltdoc="x">object-name</a></span><span class="hspace"> </span><span class="RktVar">in</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~2
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encapsulates S-expression structure with source-location
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information. As with <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span>, when
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span> is used within the dynamic extent of
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span>, the result from
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<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span> is either a special-comment value,
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end-of-file, or opaque graph-structure placeholder (not a syntax
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object). The placeholder can be embedded in an S-expression or syntax
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object returned by a reader macro, etc., and it will be replaced with
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the actual syntax object before the outermost <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span>
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returns.</div></p><p>Using <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> within the dynamic extent of
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> does not allow graph structure for reading to be
|
||
|
|
included in the outer <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> parsing, and neither does
|
||
|
|
using <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span> within the dynamic extent of
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>. In those cases, <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> and
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span> produce results like <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span> and
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span>, except that a special-comment value is returned
|
||
|
|
when the input stream starts with a comment (after whitespace).</p><p>See <a href="readtables.html" data-pltdoc="x">Readtables</a> for an extended example that uses
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span>.</p><p class="SHistory">Changed in version 6.2 of package <span class="stt">base</span>: Adjusted use of <span class="RktVar">readtable</span>
|
||
|
|
in the same way as for
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</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._((quote._~23~25kernel)._read-language))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-language</a></span></span><span class="hspace"> </span><span class="RktOpt">[</span><span class="RktVar">in</span><span class="hspace"> </span><span class="RktVar">fail-thunk</span><span class="RktOpt">]</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="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="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="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._current-input-port%29%29" class="RktValLink" data-pltdoc="x">current-input-port</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">fail-thunk</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#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span clas
|
||
|
|
soon as a <a href="Reading.html#%28tech._reader._language%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader language</span></a> (or its absence) is determined, and
|
||
|
|
using the <a href="syntax-model.html#%28tech._current._namespace%29" class="techoutside" data-pltdoc="x"><span class="techinside">current namespace</span></a> to load a reader module instead
|
||
|
|
of its <a href="Namespaces.html#%28tech._root._namespace%29" class="techoutside" data-pltdoc="x"><span class="techinside">root namespace</span></a> (if those are different).</div></p><p>A <a name="(tech._reader._language)"></a><span style="font-style: italic">reader language</span> is specified by <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> (see <a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a>) at the beginning of the
|
||
|
|
input, though possibly after comment forms. The default
|
||
|
|
<a href="readtables.html#%28tech._readtable%29" class="techoutside" data-pltdoc="x"><span class="techinside">readtable</span></a> is used by <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span> (instead of the
|
||
|
|
value of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-readtable%29%29" class="RktValLink" data-pltdoc="x">current-readtable</a></span>), and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#reader</span><span class="hspace"></span></span> forms
|
||
|
|
(which might produce comments) are not allowed before <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span>
|
||
|
|
or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span>.</p><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="finger.png" alt="+" width="24" height="24"/></span>See also <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=language-get-info.html&version=8.6" class="Sq" data-pltdoc="x">Source-Handling Configuration</a> in <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=index.html&version=8.6" class="Sq" data-pltdoc="x">The Racket Guide</a>.</p></blockquote></blockquote></blockquote><p>When it finds a <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> specification, instead
|
||
|
|
of dispatching to a <span class="RktSym">read</span> or <span class="RktSym">read-syntax</span>
|
||
|
|
function as <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span> and <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> do,
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span> dispatches to the <span class="RktSym">get-info</span>
|
||
|
|
function (if any) exported by the same module. The arguments to
|
||
|
|
<span class="RktSym">get-info</span> are the same as for <span class="RktSym">read</span>
|
||
|
|
as described in <a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a>. The result of the
|
||
|
|
<span class="RktSym">get-info</span> function is the result of
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span> if it is a function of two arguments; if
|
||
|
|
<span class="RktSym">get-info</span> produces any other kind of result, the
|
||
|
|
<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. If no <span class="RktSym">get-info</span> function is
|
||
|
|
exported, <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span> returns <span class="RktVal">#f</span>.</p><p><div class="SIntrapara">The function produced by <span class="RktSym">get-info</span> reflects information
|
||
|
|
about the expected syntax of the input stream. The first argument to the
|
||
|
|
function serves as a key on such information; acceptable keys and the
|
||
|
|
interpretation of results is up to external tools, such as DrRacket (see
|
||
|
|
<a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?tag=%28part._%28.%27%28lib._scribblings%2Ftools%2Ftools..scrbl%29.%27._.%27lang-languages-customization.%27%29%29&version=8.6" class="Sq" data-pltdoc="x">the DrRacket documentation</a>).
|
||
|
|
If no information is available for a given key, the result should be
|
||
|
|
the second argument.
|
||
|
|
</div><div class="SIntrapara"><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">scribble-manual-info</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stringport.html#%28def._%28%28quote._~23~25kernel%29._open-input-string%29%29" class="RktValLink" data-pltdoc="x">open-input-string</a></span><span class="hspace"> </span><span class="RktVal">"#lang scribble/manual"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">scribble-manual-info</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">color-lexer</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<procedure:scribble-inside-lexer></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">scribble-manual-info</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">something-else</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote></div></p></div></p><p>The <span class="RktSym">get-info</span> function itself is applied to five
|
||
|
|
arguments: the input port being read, the module path from which the
|
||
|
|
<span class="RktSym">get-info</span> function was extracted, and the source line
|
||
|
|
(positive exact integer or <span class="RktVal">#f</span>), column (non-negative exact
|
||
|
|
integer or <span class="RktVal">#f</span>), and position (positive exact integer or
|
||
|
|
<span class="RktVal">#f</span>) of the start of the <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span>
|
||
|
|
form. The <span class="RktSym">get-info</span> function may further read from the
|
||
|
|
given input port to determine its result, but it should read no
|
||
|
|
further than necessary. The <span class="RktSym">get-info</span> function should
|
||
|
|
not read from the port after returning a function.</p><p>If <span class="RktVar">in</span> starts with a <a href="Reading.html#%28tech._reader._language%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader language</span></a> specification but
|
||
|
|
the relevant module does not export <span class="RktSym">get-info</span> (but
|
||
|
|
perhaps does export <span class="RktSym">read</span> and
|
||
|
|
<span class="RktSym">read-syntax</span>), then the result of <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span>
|
||
|
|
is <span class="RktVal">#f</span>.</p><p>If <span class="RktVar">in</span> has a <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> specification,
|
||
|
|
but parsing and resolving the specification raises an exception, the
|
||
|
|
exception is propagated by <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-language%29%29" class="RktValLink" data-pltdoc="x">read-language</a></span>. Having at least
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#l</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> (after comments and whitespace) counts as
|
||
|
|
starting a <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> specification.</p><p>If <span class="RktVar">in</span> does not specify a <a href="Reading.html#%28tech._reader._language%29" class="techoutside" data-pltdoc="x"><span class="techinside">reader language</span></a> with
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span>, then <span class="RktVar">fail-thunk</span> is
|
||
|
|
called. The default <span class="RktVar">fail-thunk</span> raises
|
||
|
|
<span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3aread%29%29" class="RktValLink" data-pltdoc="x">exn:fail:read</a></span> or <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3afail~3aread~3aeof%29%29" class="RktValLink" data-pltdoc="x">exn:fail:read:eof</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-case-sensitive))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-case-sensitive%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-case-sensitive</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-case-sensitive%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-case-sensitive</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing and printing of symbols. When this
|
||
|
|
parameter’s value is <span class="RktVal">#f</span>, the reader case-folds symbols (e.g.,
|
||
|
|
producing <span class="RktVal">'</span><span class="RktVal">hi</span> when the input is any one of <span class="RktInBG"><span class="hspace"></span><span class="RktIn">hi</span><span class="hspace"></span></span>,
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">Hi</span><span class="hspace"></span></span>, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">HI</span><span class="hspace"></span></span>, or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">hI</span><span class="hspace"></span></span>). The parameter also
|
||
|
|
affects the way that <span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._write%29%29" class="RktValLink" data-pltdoc="x">write</a></span> prints symbols containing
|
||
|
|
uppercase characters; if the parameter’s value is <span class="RktVal">#f</span>, then
|
||
|
|
symbols are printed with uppercase characters quoted by a
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">\</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">|</span><span class="hspace"></span></span>. The parameter’s value is overridden by
|
||
|
|
quoting <span class="RktInBG"><span class="hspace"></span><span class="RktIn">\</span><span class="hspace"></span></span> or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">|</span><span class="hspace"></span></span> vertical-bar quotes and the
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#cs</span><span class="hspace"></span></span> and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#ci</span><span class="hspace"></span></span> prefixes; see
|
||
|
|
<a href="reader.html#%28part._parse-symbol%29" data-pltdoc="x">Reading Symbols</a> for more information. While a module is
|
||
|
|
loaded, the parameter is set to <span class="RktVal">#t</span> (see
|
||
|
|
<span class="RktSym"><a href="eval.html#%28def._%28%28quote._~23~25kernel%29._current-load%29%29" class="RktValLink" data-pltdoc="x">current-load</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-square-bracket-as-paren))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-square-bracket-as-paren%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-square-bracket-as-paren</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-square-bracket-as-paren%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-square-bracket-as-paren</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">[</span><span class="hspace"></span></span> and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">]</span><span class="hspace"></span></span>
|
||
|
|
are treated as parentheses. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more
|
||
|
|
information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-curly-brace-as-paren))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-curly-brace-as-paren%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-curly-brace-as-paren</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-curly-brace-as-paren%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-curly-brace-as-paren</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">{</span><span class="hspace"></span></span> and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">}</span><span class="hspace"></span></span>
|
||
|
|
are treated as parentheses. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more
|
||
|
|
information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-square-bracket-with-tag))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-square-bracket-with-tag%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-square-bracket-with-tag</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-square-bracket-with-tag%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-square-bracket-with-tag</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">[</span><span class="hspace"></span></span> and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">]</span><span class="hspace"></span></span>
|
||
|
|
are treated as parentheses, but the resulting list tagged with
|
||
|
|
<span class="RktSym">#%brackets</span>. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more information.</div></p><p class="SHistory">Added in version 6.3.0.5 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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-curly-brace-with-tag))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-curly-brace-with-tag%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-curly-brace-with-tag</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-curly-brace-with-tag%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-curly-brace-with-tag</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">{</span><span class="hspace"></span></span> and
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">}</span><span class="hspace"></span></span> are treated as parentheses, but the resulting list
|
||
|
|
tagged with <span class="RktSym">#%braces</span>. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more
|
||
|
|
information.</div></p><p class="SHistory">Added in version 6.3.0.5 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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-box))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-box%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-box</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-box%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-box</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#&</span><span class="hspace"></span></span> input. See
|
||
|
|
<a href="reader.html#%28part._parse-box%29" data-pltdoc="x">Reading Boxes</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-compiled))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-compiled%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-compiled</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-compiled%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-compiled</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#~</span><span class="hspace"></span></span> compiled input. See
|
||
|
|
<a href="reader.html" data-pltdoc="x">The Reader</a> and <span class="RktSym"><a href="eval.html#%28def._%28%28quote._~23~25kernel%29._current-compile%29%29" class="RktValLink" data-pltdoc="x">current-compile</a></span> for more
|
||
|
|
information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-bar-quote))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-bar-quote%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-bar-quote</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-bar-quote%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-bar-quote</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing and printing of <span class="RktInBG"><span class="hspace"></span><span class="RktIn">|</span><span class="hspace"></span></span> in
|
||
|
|
symbols. See <a href="reader.html#%28part._parse-symbol%29" data-pltdoc="x">Reading Symbols</a> and <a href="printing.html" data-pltdoc="x">The Printer</a> for
|
||
|
|
more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-graph))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-graph%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-graph</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-graph%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-graph</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A parameter value that controls parsing input with sharing in
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span> mode. See <a href="reader.html#%28part._parse-graph%29" data-pltdoc="x">Reading Graph Structure</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-syntax-accept-graph))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax-accept-graph%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-syntax-accept-graph</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax-accept-graph%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-syntax-accept-graph</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A parameter value that controls parsing input with sharing in
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> mode. See <a href="reader.html#%28part._parse-graph%29" data-pltdoc="x">Reading Graph Structure</a> for more information.</div></p><p class="SHistory">Added in version 8.4.0.8 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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-decimal-as-inexact))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-decimal-as-inexact%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-decimal-as-inexact</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-decimal-as-inexact%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-decimal-as-inexact</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input numbers with a decimal point
|
||
|
|
or exponent (but no explicit exactness tag). See
|
||
|
|
<a href="reader.html#%28part._parse-number%29" data-pltdoc="x">Reading Numbers</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-single-flonum))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-single-flonum%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-single-flonum</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-single-flonum%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-single-flonum</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input numbers that have a
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">f</span><span class="hspace"></span></span>, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">F</span><span class="hspace"></span></span>, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">s</span><span class="hspace"></span></span>, or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">S</span><span class="hspace"></span></span> precision
|
||
|
|
character. See <a href="reader.html#%28part._parse-number%29" data-pltdoc="x">Reading Numbers</a> for more information.</div></p><p class="SHistory">Added in version 7.3.0.5 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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-dot))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-dot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-dot</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-dot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-dot</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input with a dot, which is normally
|
||
|
|
used for literal cons cells. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more
|
||
|
|
information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-infix-dot))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-infix-dot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-infix-dot</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-infix-dot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-infix-dot</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input with two dots to trigger infix
|
||
|
|
conversion. See <a href="reader.html#%28part._parse-pair%29" data-pltdoc="x">Reading Pairs and Lists</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-cdot))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-cdot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-cdot</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-cdot%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-cdot</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input with a dot, in a C
|
||
|
|
structure accessor style. See <a href="reader.html#%28part._parse-cdot%29" data-pltdoc="x">Reading with C-style Infix-Dot Notation</a> for more
|
||
|
|
information.</div></p><p class="SHistory">Added in version 6.3.0.5 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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-quasiquote))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-quasiquote%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-quasiquote</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-quasiquote%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-quasiquote</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls parsing input with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">`</span><span class="hspace"></span></span> or
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">,</span><span class="hspace"></span></span> which is normally used for <span class="RktSym"><a href="quasiquote.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._quasiquote%29%29" class="RktStxLink" data-pltdoc="x">quasiquote</a></span>,
|
||
|
|
<span class="RktSym"><a href="quasiquote.html#%28form._%28%28quote._~23~25kernel%29._unquote%29%29" class="RktStxLink" data-pltdoc="x">unquote</a></span>, and <span class="RktSym"><a href="quasiquote.html#%28form._%28%28quote._~23~25kernel%29._unquote-splicing%29%29" class="RktStxLink" data-pltdoc="x">unquote-splicing</a></span> abbreviations. See
|
||
|
|
<a href="reader.html#%28part._parse-quote%29" data-pltdoc="x">Reading Quotes</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-reader))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-reader%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-reader</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-reader%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-reader</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that controls whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#reader</span><span class="hspace"></span></span>, <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span>,
|
||
|
|
or <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> are allowed for selecting a parser. See
|
||
|
|
<a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-accept-lang))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-lang%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-lang</a></span></span><span class="RktPn"></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="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-lang%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-accept-lang</a></span></span><span class="hspace"> </span><span class="RktVar">on?</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">on?</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that (along with <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-accept-reader%29%29" class="RktValLink" data-pltdoc="x">read-accept-reader</a></span>) controls
|
||
|
|
whether <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#lang</span><span class="hspace"></span></span> and <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#!</span><span class="hspace"></span></span> are allowed for selecting a
|
||
|
|
parser. See <a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._current-readtable))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-readtable%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-readtable</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="readtables.html#%28def._%28%28quote._~23~25kernel%29._readtable~3f%29%29" class="RktValLink" data-pltdoc="x">readtable?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-readtable%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-readtable</a></span></span><span class="hspace"> </span><span class="RktVar">readtable</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">readtable</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="readtables.html#%28def._%28%28quote._~23~25kernel%29._readtable~3f%29%29" class="RktValLink" data-pltdoc="x">readtable?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">A parameter whose value determines a readtable that
|
||
|
|
adjusts the parsing of S-expression input, where <span class="RktVal">#f</span> implies the
|
||
|
|
default behavior. See <a href="readtables.html" data-pltdoc="x">Readtables</a> for more information.</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/private/misc..rkt)._call-with-default-reading-parameterization))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._call-with-default-reading-parameterization%29%29" class="RktValDef RktValLink" data-pltdoc="x">call-with-default-reading-parameterization</a></span></span><span class="hspace"> </span><span class="RktVar">thunk</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">thunk</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#%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></table></blockquote></div><div class="SIntrapara">Calls <span class="RktVar">thunk</span> in <a href="eval-model.html#%28tech._tail._position%29" class="techoutside" data-pltdoc="x"><span class="techinside">tail position</span></a> of a <span class="RktSym"><a href="parameters.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._parameterize%29%29" class="RktStxLink" data-pltdoc="x">parameterize</a></span>
|
||
|
|
to set all reader <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameters</span></a> above to their default values.</div></p><p>Using the default parameter values ensures consistency, and it also
|
||
|
|
provides safety when reading from untrusted sources, since the default
|
||
|
|
values disable evaluation of arbitrary code via <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=guide&rel=Module_Syntax.html%23%2528part._hash-lang%2529&version=8.6" class="RktModLink Sq" data-pltdoc="x"><span class="RktMod">#lang</span></a> or
|
||
|
|
<span class="RktInBG"><span class="hspace"></span><span class="RktIn">#reader</span><span class="hspace"></span></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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._current-reader-guard))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-reader-guard%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-reader-guard</a></span></span><span class="RktPn"></span><span class="RktPn">)</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%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="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="RktPn"> .</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></p></blockquote></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._current-reader-guard%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-reader-guard</a></span></span><span class="hspace"> </span><span class="RktVar">proc</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">proc</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%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="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="RktPn"> .</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></table></blockquote></div><div class="SIntrapara">A parameter whose value converts or rejects (by raising an exception)
|
||
|
|
a module-path datum following <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#reader</span><span class="hspace"></span></span>. See
|
||
|
|
<a href="reader.html#%28part._parse-reader%29" data-pltdoc="x">Reading via an Extension</a> for more information.</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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._read-on-demand-source))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-on-demand-source%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-on-demand-source</a></span></span><span class="RktPn"></span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#t</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="Manipulating_Paths.html#%28def._%28%28quote._~23~25kernel%29._path~3f%29%29" class="RktValLink" data-pltdoc="x">path?</a></span><span class="hspace"> </span><span class="RktSym"><a href="Manipulating_Paths.html#%28def._%28%28quote._~23~25kernel%29._complete-path~3f%29%29" class="RktValLink" data-pltdoc="x">complete-path?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-on-demand-source%29%29" class="RktValDef RktValLink" data-pltdoc="x">read-on-demand-source</a></span></span><span class="hspace"> </span><span class="RktVar">mode</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">mode</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#t</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="Manipulating_Paths.html#%28def._%28%28quote._~23~25kernel%29._path~3f%29%29" class="RktValLink" data-pltdoc="x">path?</a></span><span class="hspace"> </span><span class="RktSym"><a href="Manipulating_Paths.html#%28def._%28%28quote._~23~25kernel%29._complete-path~3f%29%29" class="RktValLink" data-pltdoc="x">complete-path?</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that enables lazy parsing of compiled code, so that
|
||
|
|
closure bodies and syntax objects are extracted (and validated) from
|
||
|
|
marshaled compiled code on demand. Normally, this parameter is set by
|
||
|
|
the default <a href="eval.html#%28tech._load._handler%29" class="techoutside" data-pltdoc="x"><span class="techinside">load handler</span></a> when <span class="RktSym"><a href="eval.html#%28def._%28%28quote._~23~25kernel%29._load-on-demand-enabled%29%29" class="RktValLink" data-pltdoc="x">load-on-demand-enabled</a></span>
|
||
|
|
is <span class="RktVal">#t</span>.</div></p><p>A <span class="RktVal">#f</span> value for <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-on-demand-source%29%29" class="RktValLink" data-pltdoc="x">read-on-demand-source</a></span> disables lazy
|
||
|
|
parsing of compiled code. A <span class="RktVal">#t</span> value enables lazy parsing. A
|
||
|
|
<a href="pathutils.html#%28tech._path%29" class="techoutside" data-pltdoc="x"><span class="techinside">path</span></a> value furthers enable lazy retrieval from disk—<wbr></wbr>instead
|
||
|
|
of keeping unparsed compiled code in memory—<wbr></wbr>when the
|
||
|
|
<a name="(idx._(gentag._268._(lib._scribblings/reference/reference..scrbl)))"></a><span class="stt">PLT_DELAY_FROM_ZO</span> environment variable is set (to
|
||
|
|
any value) on start-up.</p><p>If the file at <span class="RktVar">mode</span> as a <a href="pathutils.html#%28tech._path%29" class="techoutside" data-pltdoc="x"><span class="techinside">path</span></a> changes before the
|
||
|
|
delayed code is parsed when lazy retrieval from disk is enabled, then
|
||
|
|
the on-demand parse most likely will encounter garbage, leading to an
|
||
|
|
exception.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._port-read-handler))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._port-read-handler%29%29" class="RktValDef RktValLink" data-pltdoc="x">port-read-handler</a></span></span><span class="hspace"> </span><span class="RktVar">in</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._case-~3e%29%29" class="RktStxLink" data-pltdoc="x">case-></a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</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="RktPn">(</span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="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="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="port-ops.html#%28def._%28%28quote._~23~25kernel%29._input-port~3f%29%29" class="RktValLink" data-pltdoc="x">input-port?</a></span></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._port-read-handler%29%29" class="RktValDef RktValLink" data-pltdoc="x">port-read-handler</a></span></span><span class="hspace"> </span><span class="RktVar">in</span><span class="hspace"> </span><span class="RktVar">proc</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></td></tr><tr><
|
||
|
|
handler called to read from the port when the built-in <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>
|
||
|
|
or <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span> procedure is applied to the port. (The
|
||
|
|
port read handler is not used for <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read/recursive</a></span> or
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%2Frecursive%29%29" class="RktValLink" data-pltdoc="x">read-syntax/recursive</a></span>.)</div></p><p>A port read handler is applied to either one argument or two
|
||
|
|
arguments:</p><ul><li><p>A single argument is supplied when the port is used
|
||
|
|
with <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>; the argument is the port being read. The return
|
||
|
|
value is the value that was read from the port (or end-of-file).</p></li><li><p>Two arguments are supplied when the port is used with
|
||
|
|
<span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read-syntax%29%29" class="RktValLink" data-pltdoc="x">read-syntax</a></span>; the first argument is the port being read, and
|
||
|
|
the second argument is a value indicating the source. The return
|
||
|
|
value is a syntax object that was read from the port (or end-of-file).</p></li></ul><p>The default port read handler reads standard Racket expressions with
|
||
|
|
Racket’s built-in parser (see <a href="reader.html" data-pltdoc="x">The Reader</a>). It handles a
|
||
|
|
special result from a custom input port (see
|
||
|
|
<span class="RktSym"><a href="customport.html#%28def._%28%28quote._~23~25kernel%29._make-input-port%29%29" class="RktValLink" data-pltdoc="x">make-input-port</a></span>) by treating it as a single expression,
|
||
|
|
except that special-comment values (see
|
||
|
|
<a href="special-comments.html" data-pltdoc="x">Special Comments</a>) are treated as whitespace.</p><p>The default port read handler itself can be customized through a
|
||
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