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206 lines
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Fly Evaluation (Guile Reference Manual)</title>
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<div class="subsection-level-extent" id="Fly-Evaluation">
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<p>
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Next: <a href="Compilation.html" accesskey="n" rel="next">Compiling Scheme Code</a>, Previous: <a href="Scheme-Write.html" accesskey="p" rel="prev">Writing Scheme Values</a>, Up: <a href="Read_002fLoad_002fEval_002fCompile.html" accesskey="u" rel="up">Reading and Evaluating Scheme Code</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="subsection" id="Procedures-for-On-the-Fly-Evaluation"><span>6.16.5 Procedures for On the Fly Evaluation<a class="copiable-link" href="#Procedures-for-On-the-Fly-Evaluation"> ¶</a></span></h4>
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<p>Scheme has the lovely property that its expressions may be represented
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as data. The <code class="code">eval</code> procedure takes a Scheme datum and evaluates
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it as code.
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</p>
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<a class="index-entry-id" id="index-eval-2"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-eval"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">eval</strong> <var class="def-var-arguments">exp module_or_state</var><a class="copiable-link" href="#index-eval"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005feval"><span class="category-def">C Function: </span><span><strong class="def-name">scm_eval</strong> <var class="def-var-arguments">(exp, module_or_state)</var><a class="copiable-link" href="#index-scm_005feval"> ¶</a></span></dt>
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<dd><p>Evaluate <var class="var">exp</var>, a list representing a Scheme expression,
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in the top-level environment specified by <var class="var">module_or_state</var>.
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While <var class="var">exp</var> is evaluated (using <code class="code">primitive-eval</code>),
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<var class="var">module_or_state</var> is made the current module. The current module
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is reset to its previous value when <code class="code">eval</code> returns.
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XXX - dynamic states.
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Example: (eval ’(+ 1 2) (interaction-environment))
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</p></dd></dl>
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<a class="index-entry-id" id="index-interaction_002denvironment-1"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-interaction_002denvironment"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">interaction-environment</strong><a class="copiable-link" href="#index-interaction_002denvironment"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005finteraction_005fenvironment"><span class="category-def">C Function: </span><span><strong class="def-name">scm_interaction_environment</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005finteraction_005fenvironment"> ¶</a></span></dt>
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<dd><p>Return a specifier for the environment that contains
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implementation–defined bindings, typically a superset of those
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listed in the report. The intent is that this procedure will
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return the environment in which the implementation would
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evaluate expressions dynamically typed by the user.
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</p></dd></dl>
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<p>See <a class="xref" href="Environments.html">Environments</a>, for other environments.
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</p>
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<p>One does not always receive code as Scheme data, of course, and this is
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especially the case for Guile’s other language implementations
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(see <a class="pxref" href="Other-Languages.html">Support for Other Languages</a>). For the case in which all you have is a
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string, we have <code class="code">eval-string</code>. There is a legacy version of this
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procedure in the default environment, but you really want the one from
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<code class="code">(ice-9 eval-string)</code>, so load it up:
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</p>
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<div class="example">
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<pre class="example-preformatted">(use-modules (ice-9 eval-string))
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-eval_002dstring"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">eval-string</strong> <var class="def-var-arguments">string [#:module=#f] [#:file=#f] [#:line=#f] [#:column=#f] [#:lang=(current-language)] [#:compile?=#f]</var><a class="copiable-link" href="#index-eval_002dstring"> ¶</a></span></dt>
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<dd><p>Parse <var class="var">string</var> according to the current language, normally Scheme.
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Evaluate or compile the expressions it contains, in order, returning the
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last expression.
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</p>
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<p>If the <var class="var">module</var> keyword argument is set, save a module excursion
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(see <a class="pxref" href="Module-System-Reflection.html">Module System Reflection</a>) and set the current module to
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<var class="var">module</var> before evaluation.
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</p>
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<p>The <var class="var">file</var>, <var class="var">line</var>, and <var class="var">column</var> keyword arguments can be
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used to indicate that the source string begins at a particular source
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location.
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</p>
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<p>Finally, <var class="var">lang</var> is a language, defaulting to the current language,
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and the expression is compiled if <var class="var">compile?</var> is true or there is no
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evaluator for the given language.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-scm_005feval_005fstring"><span class="category-def">C Function: </span><span><strong class="def-name">scm_eval_string</strong> <var class="def-var-arguments">(string)</var><a class="copiable-link" href="#index-scm_005feval_005fstring"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005feval_005fstring_005fin_005fmodule"><span class="category-def">C Function: </span><span><strong class="def-name">scm_eval_string_in_module</strong> <var class="def-var-arguments">(string, module)</var><a class="copiable-link" href="#index-scm_005feval_005fstring_005fin_005fmodule"> ¶</a></span></dt>
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<dd><p>These C bindings call <code class="code">eval-string</code> from <code class="code">(ice-9
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eval-string)</code>, evaluating within <var class="var">module</var> or the current module.
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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_005feval_005fstring"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_c_eval_string</strong> <code class="def-code-arguments">(const char *string)</code><a class="copiable-link" href="#index-scm_005fc_005feval_005fstring"> ¶</a></span></dt>
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<dd><p><code class="code">scm_eval_string</code>, but taking a C string in locale encoding instead
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of an <code class="code">SCM</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-apply"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">apply</strong> <var class="def-var-arguments">proc arg … arglst</var><a class="copiable-link" href="#index-apply"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fapply_005f0"><span class="category-def">C Function: </span><span><strong class="def-name">scm_apply_0</strong> <var class="def-var-arguments">(proc, arglst)</var><a class="copiable-link" href="#index-scm_005fapply_005f0"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fapply_005f1"><span class="category-def">C Function: </span><span><strong class="def-name">scm_apply_1</strong> <var class="def-var-arguments">(proc, arg1, arglst)</var><a class="copiable-link" href="#index-scm_005fapply_005f1"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fapply_005f2"><span class="category-def">C Function: </span><span><strong class="def-name">scm_apply_2</strong> <var class="def-var-arguments">(proc, arg1, arg2, arglst)</var><a class="copiable-link" href="#index-scm_005fapply_005f2"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fapply_005f3"><span class="category-def">C Function: </span><span><strong class="def-name">scm_apply_3</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arglst)</var><a class="copiable-link" href="#index-scm_005fapply_005f3"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fapply"><span class="category-def">C Function: </span><span><strong class="def-name">scm_apply</strong> <var class="def-var-arguments">(proc, arg, rest)</var><a class="copiable-link" href="#index-scm_005fapply"> ¶</a></span></dt>
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<dd><a class="index-entry-id" id="index-apply-2"></a>
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<p>Call <var class="var">proc</var> with arguments <var class="var">arg</var> … and the
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elements of the <var class="var">arglst</var> list.
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</p>
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<p><code class="code">scm_apply</code> takes parameters corresponding to a Scheme level
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<code class="code">(lambda (proc arg1 . rest) ...)</code>. So <var class="var">arg1</var> and all but the
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last element of the <var class="var">rest</var> list make up <var class="var">arg</var> …, and the
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last element of <var class="var">rest</var> is the <var class="var">arglst</var> list. Or if <var class="var">rest</var>
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is the empty list <code class="code">SCM_EOL</code> then there’s no <var class="var">arg</var> …, and
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(<var class="var">arg1</var>) is the <var class="var">arglst</var>.
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</p>
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<p><var class="var">arglst</var> is not modified, but the <var class="var">rest</var> list passed to
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<code class="code">scm_apply</code> is modified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-scm_005fcall_005f0"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_0</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fcall_005f0"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f1"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_1</strong> <var class="def-var-arguments">(proc, arg1)</var><a class="copiable-link" href="#index-scm_005fcall_005f1"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f2"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_2</strong> <var class="def-var-arguments">(proc, arg1, arg2)</var><a class="copiable-link" href="#index-scm_005fcall_005f2"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f3"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_3</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3)</var><a class="copiable-link" href="#index-scm_005fcall_005f3"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f4"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_4</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4)</var><a class="copiable-link" href="#index-scm_005fcall_005f4"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f5"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_5</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4, arg5)</var><a class="copiable-link" href="#index-scm_005fcall_005f5"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f6"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_6</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4, arg5, arg6)</var><a class="copiable-link" href="#index-scm_005fcall_005f6"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f7"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_7</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4, arg5, arg6, arg7)</var><a class="copiable-link" href="#index-scm_005fcall_005f7"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f8"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_8</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8)</var><a class="copiable-link" href="#index-scm_005fcall_005f8"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcall_005f9"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_9</strong> <var class="def-var-arguments">(proc, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9)</var><a class="copiable-link" href="#index-scm_005fcall_005f9"> ¶</a></span></dt>
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<dd><p>Call <var class="var">proc</var> with the given arguments.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-scm_005fcall"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call</strong> <var class="def-var-arguments">(proc, ...)</var><a class="copiable-link" href="#index-scm_005fcall"> ¶</a></span></dt>
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<dd><p>Call <var class="var">proc</var> with any number of arguments. The argument list must be
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terminated by <code class="code">SCM_UNDEFINED</code>. For example:
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</p>
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<div class="example">
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<pre class="example-preformatted">scm_call (scm_c_public_ref ("guile", "+"),
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scm_from_int (1),
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scm_from_int (2),
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SCM_UNDEFINED);
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</pre></div>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-scm_005fcall_005fn"><span class="category-def">C Function: </span><span><strong class="def-name">scm_call_n</strong> <var class="def-var-arguments">(proc, argv, nargs)</var><a class="copiable-link" href="#index-scm_005fcall_005fn"> ¶</a></span></dt>
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<dd><p>Call <var class="var">proc</var> with the array of arguments <var class="var">argv</var>, as a
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<code class="code">SCM*</code>. The length of the arguments should be passed in
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<var class="var">nargs</var>, as a <code class="code">size_t</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-primitive_002deval"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">primitive-eval</strong> <var class="def-var-arguments">exp</var><a class="copiable-link" href="#index-primitive_002deval"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprimitive_005feval"><span class="category-def">C Function: </span><span><strong class="def-name">scm_primitive_eval</strong> <var class="def-var-arguments">(exp)</var><a class="copiable-link" href="#index-scm_005fprimitive_005feval"> ¶</a></span></dt>
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<dd><p>Evaluate <var class="var">exp</var> in the top-level environment specified by
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the current module.
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</p></dd></dl>
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</div>
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<hr>
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Next: <a href="Compilation.html">Compiling Scheme Code</a>, Previous: <a href="Scheme-Write.html">Writing Scheme Values</a>, Up: <a href="Read_002fLoad_002fEval_002fCompile.html">Reading and Evaluating Scheme Code</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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