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Previous: <a href="Keywords.html" accesskey="p" rel="prev">Keywords</a>, Up: <a href="Grammar-and-Parser.html" accesskey="u" rel="up">Grammar and Parser</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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<h3 class="section" id="Parser-1"><span>F.2 Parser<a class="copiable-link" href="#Parser-1"> ¶</a></span></h3>
<a class="index-entry-id" id="index-parser"></a>
<p>The parser has a number of variables that affect its internal operation.
These variables are generally documented in the manual alongside the code that
they affect.
</p>
<p>In addition, there are three non-specific parser customization functions.
<code class="code">add_input_event_hook</code> can be used to schedule a user function for
periodic evaluation. <code class="code">remove_input_event_hook</code> will stop a user function
from being evaluated periodically.
</p>
<a class="anchor" id="XREFadd_005finput_005fevent_005fhook"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-add_005finput_005fevent_005fhook"><span><code class="def-type"><var class="var">id</var> =</code> <strong class="def-name">add_input_event_hook</strong> <code class="def-code-arguments">(<var class="var">fcn</var>)</code><a class="copiable-link" href="#index-add_005finput_005fevent_005fhook"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-add_005finput_005fevent_005fhook-1"><span><code class="def-type"><var class="var">id</var> =</code> <strong class="def-name">add_input_event_hook</strong> <code class="def-code-arguments">(<var class="var">fcn</var>, <var class="var">data</var>)</code><a class="copiable-link" href="#index-add_005finput_005fevent_005fhook-1"> ¶</a></span></dt>
<dd><p>Add the named function or function handle <var class="var">fcn</var> to the list of functions
to call periodically when Octave is waiting for input.
</p>
<p>The function should have the form
</p>
<div class="example">
<pre class="example-preformatted"><var class="var">fcn</var> (<var class="var">data</var>)
</pre></div>
<p>If <var class="var">data</var> is omitted, Octave calls the function without any arguments.
</p>
<p>The returned identifier may be used to remove the function handle from the
list of input hook functions.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFremove_005finput_005fevent_005fhook">remove_input_event_hook</a>.
</p></dd></dl>
<a class="anchor" id="XREFremove_005finput_005fevent_005fhook"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-remove_005finput_005fevent_005fhook"><span><strong class="def-name">remove_input_event_hook</strong> <code class="def-code-arguments">(<var class="var">name</var>)</code><a class="copiable-link" href="#index-remove_005finput_005fevent_005fhook"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-remove_005finput_005fevent_005fhook-1"><span><strong class="def-name">remove_input_event_hook</strong> <code class="def-code-arguments">(<var class="var">fcn_id</var>)</code><a class="copiable-link" href="#index-remove_005finput_005fevent_005fhook-1"> ¶</a></span></dt>
<dd><p>Remove the named function or function handle with the given identifier
from the list of functions to call periodically when Octave is waiting
for input.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFadd_005finput_005fevent_005fhook">add_input_event_hook</a>.
</p></dd></dl>
<p>Finally, when the parser cannot identify an input token it calls a particular
function to handle this. By default, this is the internal function
<code class="code">"__unimplemented__"</code> which makes suggestions about possible Octave
substitutes for <small class="sc">MATLAB</small> functions.
</p>
<a class="anchor" id="XREFmissing_005ffunction_005fhook"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-missing_005ffunction_005fhook"><span><code class="def-type"><var class="var">val</var> =</code> <strong class="def-name">missing_function_hook</strong> <code class="def-code-arguments">()</code><a class="copiable-link" href="#index-missing_005ffunction_005fhook"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-missing_005ffunction_005fhook-1"><span><code class="def-type"><var class="var">old_val</var> =</code> <strong class="def-name">missing_function_hook</strong> <code class="def-code-arguments">(<var class="var">new_val</var>)</code><a class="copiable-link" href="#index-missing_005ffunction_005fhook-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-missing_005ffunction_005fhook-2"><span><code class="def-type"><var class="var">old_val</var> =</code> <strong class="def-name">missing_function_hook</strong> <code class="def-code-arguments">(<var class="var">new_val</var>, "local")</code><a class="copiable-link" href="#index-missing_005ffunction_005fhook-2"> ¶</a></span></dt>
<dd><p>Query or set the internal variable that specifies the function to call
to provide extra information when an unknown identifier is referenced.
</p>
<p>When called from inside a function with the <code class="code">"local"</code> option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Missing-Components.html#XREFmissing_005fcomponent_005fhook">missing_component_hook</a>.
</p></dd></dl>
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