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<title>Parser - GNU Octave</title>
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Previous: <a rel="previous" accesskey="p" href="Keywords.html#Keywords">Keywords</a>,
Up: <a rel="up" accesskey="u" href="Grammar-and-Parser.html#Grammar-and-Parser">Grammar and Parser</a>
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<h3 class="section">I.2 Parser</h3>
<p><a name="index-parser-3464"></a>
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. For example, <code>allow_noninteger_range_as_index</code> is discussed
in the section on index expressions.
<p>In addition, there are three non-specific parser customization functions.
<code>add_input_event_hook</code> can be used to schedule a user function for
periodic evaluation. <code>remove_input_event_hook</code> will stop a user function
from being evaluated periodically.
<!-- add_input_event_hook src/input.cc -->
<p><a name="doc_002dadd_005finput_005fevent_005fhook"></a>
<div class="defun">
— Built-in Function: <b>add_input_event_hook</b> (<var>fcn</var>)<var><a name="index-add_005finput_005fevent_005fhook-3465"></a></var><br>
— Built-in Function: <b>add_input_event_hook</b> (<var>fcn, data</var>)<var><a name="index-add_005finput_005fevent_005fhook-3466"></a></var><br>
<blockquote><p>Add the named function <var>fcn</var> to the list of functions to call
periodically when Octave is waiting for input. The function should
have the form
<pre class="example"> <var>fcn</var> (<var>data</var>)
</pre>
<p>If <var>data</var> is omitted, Octave calls the function without any
arguments.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dremove_005finput_005fevent_005fhook.html#doc_002dremove_005finput_005fevent_005fhook">remove_input_event_hook</a>.
</p></blockquote></div>
<!-- remove_input_event_hook src/input.cc -->
<p><a name="doc_002dremove_005finput_005fevent_005fhook"></a>
<div class="defun">
— Built-in Function: <b>remove_input_event_hook</b> (<var>fcn</var>)<var><a name="index-remove_005finput_005fevent_005fhook-3467"></a></var><br>
<blockquote><p>Remove the named function <var>fcn</var> from the list of functions to call
periodically when Octave is waiting for input.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dadd_005finput_005fevent_005fhook.html#doc_002dadd_005finput_005fevent_005fhook">add_input_event_hook</a>.
</p></blockquote></div>
<p>Finally, when the parser cannot identify an input token it calls a particular
function to handle this. By default, this is the function "unimplemented"
which makes suggestions about possible Octave substitutes for <span class="sc">matlab</span>
functions.
<!-- missing_function_hook src/variables.cc -->
<p><a name="doc_002dmissing_005ffunction_005fhook"></a>
<div class="defun">
— Built-in Function: <var>val</var> = <b>missing_function_hook</b> ()<var><a name="index-missing_005ffunction_005fhook-3468"></a></var><br>
— Built-in Function: <var>old_val</var> = <b>missing_function_hook</b> (<var>new_val</var>)<var><a name="index-missing_005ffunction_005fhook-3469"></a></var><br>
— Built-in Function: <b>missing_function_hook</b> (<var>new_val, "local"</var>)<var><a name="index-missing_005ffunction_005fhook-3470"></a></var><br>
<blockquote><p>Query or set the internal variable that specifies the function to call when
an unknown identifier is requested.
<p>When called from inside a function with the "local" 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></blockquote></div>
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