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<title>Keyword Procedures (Guile Reference Manual)</title>
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<div class="subsubsection-level-extent" id="Keyword-Procedures">
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<p>
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Previous: <a href="Keyword-Read-Syntax.html" accesskey="p" rel="prev">Keyword Read Syntax</a>, Up: <a href="Keywords.html" accesskey="u" rel="up">Keywords</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<h4 class="subsubsection" id="Keyword-Procedures-1"><span>6.6.7.4 Keyword Procedures<a class="copiable-link" href="#Keyword-Procedures-1"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-keyword_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">keyword?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-keyword_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fkeyword_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_keyword_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fkeyword_005fp"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if the argument <var class="var">obj</var> is a keyword, else
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<code class="code">#f</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-keyword_002d_003esymbol"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">keyword->symbol</strong> <var class="def-var-arguments">keyword</var><a class="copiable-link" href="#index-keyword_002d_003esymbol"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fkeyword_005fto_005fsymbol"><span class="category-def">C Function: </span><span><strong class="def-name">scm_keyword_to_symbol</strong> <var class="def-var-arguments">(keyword)</var><a class="copiable-link" href="#index-scm_005fkeyword_005fto_005fsymbol"> ¶</a></span></dt>
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<dd><p>Return the symbol with the same name as <var class="var">keyword</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-symbol_002d_003ekeyword"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">symbol->keyword</strong> <var class="def-var-arguments">symbol</var><a class="copiable-link" href="#index-symbol_002d_003ekeyword"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fsymbol_005fto_005fkeyword"><span class="category-def">C Function: </span><span><strong class="def-name">scm_symbol_to_keyword</strong> <var class="def-var-arguments">(symbol)</var><a class="copiable-link" href="#index-scm_005fsymbol_005fto_005fkeyword"> ¶</a></span></dt>
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<dd><p>Return the keyword with the same name as <var class="var">symbol</var>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fis_005fkeyword"><span class="category-def">C Function: </span><span><code class="def-type">int</code> <strong class="def-name">scm_is_keyword</strong> <code class="def-code-arguments">(SCM obj)</code><a class="copiable-link" href="#index-scm_005fis_005fkeyword"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">scm_is_true (scm_keyword_p (<var class="var">obj</var>))</code>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005ffrom_005flocale_005fkeyword"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_from_locale_keyword</strong> <code class="def-code-arguments">(const char *name)</code><a class="copiable-link" href="#index-scm_005ffrom_005flocale_005fkeyword"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005ffrom_005flocale_005fkeywordn"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_from_locale_keywordn</strong> <code class="def-code-arguments">(const char *name, size_t len)</code><a class="copiable-link" href="#index-scm_005ffrom_005flocale_005fkeywordn"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">scm_symbol_to_keyword (scm_from_locale_symbol
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(<var class="var">name</var>))</code> and <code class="code">scm_symbol_to_keyword (scm_from_locale_symboln
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(<var class="var">name</var>, <var class="var">len</var>))</code>, respectively.
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</p>
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<p>Note that these functions should <em class="emph">not</em> be used when <var class="var">name</var> is a
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C string constant, because there is no guarantee that the current locale
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will match that of the execution character set, used for string and
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character constants. Most modern C compilers use UTF-8 by default, so
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in such cases we recommend <code class="code">scm_from_utf8_keyword</code>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005ffrom_005flatin1_005fkeyword"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_from_latin1_keyword</strong> <code class="def-code-arguments">(const char *name)</code><a class="copiable-link" href="#index-scm_005ffrom_005flatin1_005fkeyword"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005ffrom_005futf8_005fkeyword"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_from_utf8_keyword</strong> <code class="def-code-arguments">(const char *name)</code><a class="copiable-link" href="#index-scm_005ffrom_005futf8_005fkeyword"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">scm_symbol_to_keyword (scm_from_latin1_symbol
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(<var class="var">name</var>))</code> and <code class="code">scm_symbol_to_keyword (scm_from_utf8_symbol
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(<var class="var">name</var>))</code>, respectively.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fc_005fbind_005fkeyword_005farguments"><span class="category-def">C Function: </span><span><code class="def-type">void</code> <strong class="def-name">scm_c_bind_keyword_arguments</strong> <code class="def-code-arguments">(const char *subr, SCM rest, scm_t_keyword_arguments_flags flags, SCM keyword1, SCM *argp1, …, SCM keywordN, SCM *argpN, <code class="code">SCM_UNDEFINED</code>)</code><a class="copiable-link" href="#index-scm_005fc_005fbind_005fkeyword_005farguments"> ¶</a></span></dt>
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<dd>
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<p>Extract the specified keyword arguments from <var class="var">rest</var>, which is not
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modified. If the keyword argument <var class="var">keyword1</var> is present in
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<var class="var">rest</var> with an associated value, that value is stored in the
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variable pointed to by <var class="var">argp1</var>, otherwise the variable is left
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unchanged. Similarly for the other keywords and argument pointers up to
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<var class="var">keywordN</var> and <var class="var">argpN</var>. The argument list to
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<code class="code">scm_c_bind_keyword_arguments</code> must be terminated by
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<code class="code">SCM_UNDEFINED</code>.
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</p>
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<p>Note that since the variables pointed to by <var class="var">argp1</var> through
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<var class="var">argpN</var> are left unchanged if the associated keyword argument is not
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present, they should be initialized to their default values before
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calling <code class="code">scm_c_bind_keyword_arguments</code>. Alternatively, you can
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initialize them to <code class="code">SCM_UNDEFINED</code> before the call, and then use
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<code class="code">SCM_UNBNDP</code> after the call to see which ones were provided.
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</p>
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<p>If an unrecognized keyword argument is present in <var class="var">rest</var> and
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<var class="var">flags</var> does not contain <code class="code">SCM_ALLOW_OTHER_KEYS</code>, or if
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non-keyword arguments are present and <var class="var">flags</var> does not contain
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<code class="code">SCM_ALLOW_NON_KEYWORD_ARGUMENTS</code>, an exception is raised.
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<var class="var">subr</var> should be the name of the procedure receiving the keyword
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arguments, for purposes of error reporting.
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</p>
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<p>For example:
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</p>
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<div class="example">
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<pre class="example-preformatted">SCM k_delimiter;
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SCM k_grammar;
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SCM sym_infix;
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SCM my_string_join (SCM strings, SCM rest)
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{
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SCM delimiter = SCM_UNDEFINED;
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SCM grammar = sym_infix;
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scm_c_bind_keyword_arguments ("my-string-join", rest, 0,
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k_delimiter, &delimiter,
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k_grammar, &grammar,
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SCM_UNDEFINED);
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if (SCM_UNBNDP (delimiter))
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delimiter = scm_from_utf8_string (" ");
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return scm_string_join (strings, delimiter, grammar);
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}
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void my_init ()
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{
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k_delimiter = scm_from_utf8_keyword ("delimiter");
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k_grammar = scm_from_utf8_keyword ("grammar");
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sym_infix = scm_from_utf8_symbol ("infix");
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scm_c_define_gsubr ("my-string-join", 1, 0, 1, my_string_join);
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}
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</pre></div>
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</dd></dl>
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</div>
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<hr>
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Previous: <a href="Keyword-Read-Syntax.html">Keyword Read Syntax</a>, Up: <a href="Keywords.html">Keywords</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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