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    <title>Keywords</title>
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    <section class="sect1" title="Keywords" epub:type="subchapter" id="Keywords">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both">Keywords</h2>
          </div>
        </div>
      </div>
      <p>Keywords are similar to symbols.
They are used mainly for specifying keyword arguments.
</p>
      <p>Historically keywords have been self-evaluating (you did not need to
quote them).  This has changed: you must quote a keyword if you
want a literal keyword value, and not quote it if it is used
as a keyword argument.
</p>
      <div class="literallayout">
        <p><a id="idm139667877565968" class="indexterm"/><span id="meta-keyword"/><em class="replaceable"><code>keyword</code></em> <code class="literal">::=</code> <a class="link" href="Lexical-syntax.xhtml#meta-identifier"><em class="replaceable"><code>identifier</code></em></a><code class="literal"><span class="bold"><strong>:</strong></span></code><br/>
  | <code class="literal"><span class="bold"><strong>#:</strong></span></code><a class="link" href="Lexical-syntax.xhtml#meta-identifier"><em class="replaceable"><code>identifier</code></em></a><br/>
</p>
      </div>
      <p>The two syntaxes have the same meaning: The former is nicer-looking;
the latter is more portable (and required if you use the
<code class="literal">--r7rs</code> command-line flag).
</p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p><span class="emphasis"><em>Details:</em></span>
In r7rs and other Scheme standards the colon character
does not have any special meaning, so <code class="literal">foo:</code> or <code class="literal">foo:bar</code>
are just regular identifiers.  Therefore some other Scheme variants
that have keywords (including Guile and Racket) use the <code class="literal">#:</code> syntax.
Kawa has some hacks so that <span class="emphasis"><em>most</em></span>
standard Scheme programs that have colons in identifiers will work.
However, for best compatibility, use the <code class="literal">--r7rs</code> command-line flag
(which turns colon into a regular character in a symbol), and the
<code class="literal">#:</code> syntax.
</p>
        </blockquote>
      </div>
      <p>A keyword is a single token; therefore no whitespace is allowed between
the <em class="replaceable"><code>identifier</code></em> and the colon or after the <code class="literal">#:</code>;
these characters are not considered part of the name of the keyword.
</p>
      <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667877554544" class="indexterm"/> <code class="function">keyword?</code> <em class="replaceable"><code>obj</code></em></p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Return <code class="literal">#t</code> if <em class="replaceable"><code>obj</code></em> is a keyword, and otherwise returns <code class="literal">#f</code>.
</p>
        </blockquote>
      </div>
      <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667877549968" class="indexterm"/> <code class="function">keyword-&gt;string</code> <em class="replaceable"><code>keyword</code></em></p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Returns the name of <em class="replaceable"><code>keyword</code></em> as a string.
The name does not include the final <code class="literal">#\:</code>.
</p>
        </blockquote>
      </div>
      <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667877545680" class="indexterm"/> <code class="function">string-&gt;keyword</code> <em class="replaceable"><code>string</code></em></p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Returns the keyword whose name is <em class="replaceable"><code>string</code></em>.
(The <em class="replaceable"><code>string</code></em> does not include a final <code class="literal">#\:</code>.)
</p>
        </blockquote>
      </div>
    </section>
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