18 lines
22 KiB
HTML
18 lines
22 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>4.10 Quoting: quote and '</title><link rel="stylesheet" type="text/css" href="../scribble.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 Guide</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="intro.html" class="tocviewlink" data-pltdoc="x">Welcome to Racket</a></td></tr><tr><td align="right">2 </td><td><a href="to-scheme.html" class="tocviewlink" data-pltdoc="x">Racket Essentials</a></td></tr><tr><td align="right">3 </td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4 </td><td><a href="scheme-forms.html" class="tocviewselflink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5 </td><td><a href="define-struct.html" class="tocviewlink" data-pltdoc="x">Programmer-<wbr></wbr>Defined Datatypes</a></td></tr><tr><td align="right">6 </td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8 </td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9 </td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Exceptions and Control</a></td></tr><tr><td align="right">11 </td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions</a></td></tr><tr><td align="right">12 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">13 </td><td><a href="classes.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">14 </td><td><a href="units.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">15 </td><td><a href="reflection.html" class="tocviewlink" data-pltdoc="x">Reflection and Dynamic Evaluation</a></td></tr><tr><td align="right">16 </td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">17 </td><td><a href="languages.html" class="tocviewlink" data-pltdoc="x">Creating Languages</a></td></tr><tr>
|
||
|
|
that the <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Reading.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read</a></span> function parses as a single element. The value
|
||
|
|
of the <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">quote</a></span> form is the same value that <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Reading.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read</a></span> would
|
||
|
|
produce given <span class="RktVar">datum</span>.</p><p>The <span class="RktVar">datum</span> can be a symbol, a boolean, a number, a (character
|
||
|
|
or byte) string, a character, a keyword, an empty list, a pair (or
|
||
|
|
list) containing more such values, a vector containing more such
|
||
|
|
values, a hash table containing more such values, or a box containing
|
||
|
|
another such value.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktSym">apple</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'apple</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktVal">#t</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktVal">42</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">42</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'()</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">#</span><span class="RktVal">(</span><span class="RktVal">"z"</span><span class="hspace"> </span><span class="RktVal">x</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym">the-end</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'((1 2 3) #("z" x) . the-end)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktPn">.</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">'(1 2 3)</span></p></td></tr></table></blockquote></div></p><p>As the last example above shows, the <span class="RktVar">datum</span> does not have to
|
||
|
|
match the normalized printed form of a value. A <span class="RktVar">datum</span> cannot
|
||
|
|
be a printed representation that starts with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#<</span><span class="hspace"></span></span>, so it
|
||
|
|
cannot be <a href="void_undefined.html" class="RktModLink" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<void></span></span></a>, <a href="void_undefined.html" class="RktModLink" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<undefined></span></span></a>, or a procedure.</p><p>The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">quote</a></span> form is rarely used for a <span class="RktVar">datum</span> that is a
|
||
|
|
boolean, number, or string by itself, since the printed forms of those
|
||
|
|
values can already be used as constants. The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">quote</a></span> form is
|
||
|
|
more typically used for symbols and lists, which have other meanings
|
||
|
|
(identifiers, function calls, etc.) when not quoted.</p><p>An expression</p><blockquote class="leftindent"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><span class="RktVal">'</span><span class="RktVar">datum</span></td></tr></table></blockquote></blockquote><p>is a shorthand for</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktKw">quote</span><span class="hspace"> </span><span class="RktVar">datum</span><span class="RktPn">)</span></p></blockquote><p>and this shorthand is almost always used instead of
|
||
|
|
<span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">quote</a></span>. The shorthand applies even within the <span class="RktVar">datum</span>,
|
||
|
|
so it can produce a list containing <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=quote.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._quote%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">quote</a></span>.</p><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="magnify.png" alt="+" width="24" height="24"/></span><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=reader.html%23%2528part._parse-quote%2529&version=8.6" class="Sq" data-pltdoc="x">Reading Quotes</a> in <a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=index.html&version=8.6" class="Sq" data-pltdoc="x">The Racket Reference</a> provides more on the <span class="RktVal">'</span> shorthand.</p></blockquote></blockquote></blockquote><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktVal">'</span><span class="RktVal">apple</span></td></tr><tr><td><p><span class="RktRes">'apple</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktVal">'</span><span class="RktVal">"hello"</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktVal">)</span></td></tr><tr><td><p><span class="RktRes">'(1 2 3)</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">you</span><span class="hspace"> </span><span class="RktVal">can</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">me</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">(you can (quote me))</span></p></td></tr></table></blockquote></div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="set_.html" title="backward to "4.9 Assignment: set!"" data-pltdoc="x">← prev</a> <a href="scheme-forms.html" title="up to "4 Expressions and Definitions"" data-pltdoc="x">up</a> <a href="qq.html" title="forward to "4.11 Quasiquoting: quasiquote and lsquo"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
|