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<title>Parameters In Guile - Debugging with GDB</title>
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<a name="Parameters-In-Guile"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Progspaces-In-Guile.html#Progspaces-In-Guile">Progspaces In Guile</a>,
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Previous: <a rel="previous" accesskey="p" href="Commands-In-Guile.html#Commands-In-Guile">Commands In Guile</a>,
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Up: <a rel="up" accesskey="u" href="Guile-API.html#Guile-API">Guile API</a>
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<h5 class="subsubsection">23.3.3.12 Parameters In Guile</h5>
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<p><a name="index-parameters-in-guile-2635"></a><a name="index-guile-parameters-2636"></a><a name="index-Parameter-2637"></a>You can implement new <span class="sc">gdb</span> <dfn>parameters</dfn> using Guile
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<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>.
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<p>There are many parameters that already exist and can be set in
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<span class="sc">gdb</span>. Two examples are: <code>set follow-fork</code> and
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<code>set charset</code>. Setting these parameters influences certain
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behavior in <span class="sc">gdb</span>. Similarly, you can define parameters that
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can be used to influence behavior in custom Guile scripts and commands.
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<p>A new parameter is defined with the <code>make-parameter</code> Guile function,
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and added to <span class="sc">gdb</span> with the <code>register-parameter!</code> Guile function.
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This two-step approach is taken to separate out the side-effect of adding
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the parameter to <span class="sc">gdb</span> from <code>make-parameter</code>.
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<p>Parameters are exposed to the user via the <code>set</code> and
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<code>show</code> commands. See <a href="Help.html#Help">Help</a>.
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<!-- TODO line length -->
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<div class="defun">
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— Scheme Procedure: <b>(</b><var>make-parameter name </var><span class="roman">[</span><var>#:command-class command-class</var><span class="roman">]</span> <span class="roman">[</span><var>#:parameter-type parameter-type</var>] <span class="roman">[</span><var>#:enum-list enum-list</var><span class="roman">]</span> <span class="roman">[</span><var>#:set-func set-func</var>] <span class="roman">[</span><var>#:show-func show-func</var>] <span class="roman">[</span><var>#:doc doc</var>] <span class="roman">[</span><var>#:set-doc set-doc</var>] <span class="roman">[</span><var>#:show-doc show-doc</var>] <span class="roman">[</span><var>#:initial-value initial-value</var>])<var><a name="index-g_t_0028-2638"></a></var><br>
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<blockquote>
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<p>The argument <var>name</var> is the name of the new parameter. If <var>name</var>
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consists of multiple words, then the initial words are looked for as prefix
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parameters. An example of this can be illustrated with the
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<code>set print</code> set of parameters. If <var>name</var> is
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<code>print foo</code>, then <code>print</code> will be searched as the prefix
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parameter. In this case the parameter can subsequently be accessed in
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<span class="sc">gdb</span> as <code>set print foo</code>.
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If <var>name</var> consists of multiple words, and no prefix parameter group
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can be found, an exception is raised.
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<p>The result is the <code><gdb:parameter></code> object representing the parameter.
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The parameter is not usable until it has been registered with <span class="sc">gdb</span>
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with <code>register-parameter!</code>.
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<p>The rest of the arguments are optional.
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<p>The argument <var>command-class</var> should be one of the ‘<samp><span class="samp">COMMAND_</span></samp>’ constants
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(see <a href="Commands-In-Guile.html#Commands-In-Guile">Commands In Guile</a>). This argument tells <span class="sc">gdb</span> how to
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categorize the new parameter in the help system.
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The default is <code>COMMAND_NONE</code>.
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<p>The argument <var>parameter-type</var> should be one of the ‘<samp><span class="samp">PARAM_</span></samp>’ constants
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defined below. This argument tells <span class="sc">gdb</span> the type of the new
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parameter; this information is used for input validation and
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completion. The default is <code>PARAM_BOOLEAN</code>.
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<p>If <var>parameter-type</var> is <code>PARAM_ENUM</code>, then
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<var>enum-list</var> must be a list of strings. These strings
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represent the possible values for the parameter.
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<p>If <var>parameter-type</var> is not <code>PARAM_ENUM</code>, then the presence
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of <var>enum-list</var> will cause an exception to be thrown.
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<p>The argument <var>set-func</var> is a function of one argument: <var>self</var> which
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is the <code><gdb:parameter></code> object representing the parameter.
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<span class="sc">gdb</span> will call this function when a <var>parameter</var>'s value has
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been changed via the <code>set</code> API (for example, <kbd>set foo off</kbd>).
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The value of the parameter has already been set to the new value.
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This function must return a string to be displayed to the user.
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<span class="sc">gdb</span> will add a trailing newline if the string is non-empty.
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<span class="sc">gdb</span> generally doesn't print anything when a parameter is set,
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thus typically this function should return ‘<samp><span class="samp">""</span></samp>’.
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A non-empty string result should typically be used for displaying warnings
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and errors.
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<p>The argument <var>show-func</var> is a function of two arguments: <var>self</var> which
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is the <code><gdb:parameter></code> object representing the parameter, and
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<var>svalue</var> which is the string representation of the current value.
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<span class="sc">gdb</span> will call this function when a <var>parameter</var>'s
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<code>show</code> API has been invoked (for example, <kbd>show foo</kbd>).
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This function must return a string, and will be displayed to the user.
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<span class="sc">gdb</span> will add a trailing newline.
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<p>The argument <var>doc</var> is the help text for the new parameter.
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If there is no documentation string, a default value is used.
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<p>The argument <var>set-doc</var> is the help text for this parameter's
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<code>set</code> command.
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<p>The argument <var>show-doc</var> is the help text for this parameter's
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<code>show</code> command.
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<p>The argument <var>initial-value</var> specifies the initial value of the parameter.
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If it is a function, it takes one parameter, the <code><gdb:parameter></code>
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object and its result is used as the initial value of the parameter.
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The initial value must be valid for the parameter type,
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otherwise an exception is thrown.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>register-parameter!</b><var> parameter<a name="index-register_002dparameter_0021-2639"></a></var><br>
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<blockquote><p>Add <var>parameter</var>, a <code><gdb:parameter></code> object, to <span class="sc">gdb</span>'s
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list of parameters.
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It is an error to register a parameter more than once.
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The result is unspecified.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>parameter?</b><var> object<a name="index-parameter_003f-2640"></a></var><br>
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<blockquote><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:parameter></code> object.
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Otherwise return <code>#f</code>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>parameter-value</b><var> parameter<a name="index-parameter_002dvalue-2641"></a></var><br>
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<blockquote><p>Return the value of <var>parameter</var> which may either be
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a <code><gdb:parameter></code> object or a string naming the parameter.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>set-parameter-value!</b><var> parameter new-value<a name="index-set_002dparameter_002dvalue_0021-2642"></a></var><br>
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<blockquote><p>Assign <var>parameter</var> the value of <var>new-value</var>.
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The argument <var>parameter</var> must be an object of type <code><gdb:parameter></code>.
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<span class="sc">gdb</span> does validation when assignments are made.
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</p></blockquote></div>
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<p>When a new parameter is defined, its type must be specified. The
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available types are represented by constants defined in the <code>gdb</code>
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module:
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<dl>
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<dt><code>PARAM_BOOLEAN</code><a name="index-PARAM_005fBOOLEAN-2643"></a><dd>The value is a plain boolean. The Guile boolean values, <code>#t</code>
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and <code>#f</code> are the only valid values.
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<br><dt><code>PARAM_AUTO_BOOLEAN</code><a name="index-PARAM_005fAUTO_005fBOOLEAN-2644"></a><dd>The value has three possible states: true, false, and ‘<samp><span class="samp">auto</span></samp>’. In
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Guile, true and false are represented using boolean constants, and
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‘<samp><span class="samp">auto</span></samp>’ is represented using <code>#:auto</code>.
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<br><dt><code>PARAM_UINTEGER</code><a name="index-PARAM_005fUINTEGER-2645"></a><dd>The value is an unsigned integer. The value of 0 should be
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interpreted to mean “unlimited”.
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<br><dt><code>PARAM_ZINTEGER</code><a name="index-PARAM_005fZINTEGER-2646"></a><dd>The value is an integer.
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<br><dt><code>PARAM_ZUINTEGER</code><a name="index-PARAM_005fZUINTEGER-2647"></a><dd>The value is an unsigned integer.
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<br><dt><code>PARAM_ZUINTEGER_UNLIMITED</code><a name="index-PARAM_005fZUINTEGER_005fUNLIMITED-2648"></a><dd>The value is an integer in the range ‘<samp><span class="samp">[0, INT_MAX]</span></samp>’.
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A value of ‘<samp><span class="samp">-1</span></samp>’ means “unlimited”, and other negative
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numbers are not allowed.
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<br><dt><code>PARAM_STRING</code><a name="index-PARAM_005fSTRING-2649"></a><dd>The value is a string. When the user modifies the string, any escape
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sequences, such as ‘<samp><span class="samp">\t</span></samp>’, ‘<samp><span class="samp">\f</span></samp>’, and octal escapes, are
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translated into corresponding characters and encoded into the current
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host charset.
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<br><dt><code>PARAM_STRING_NOESCAPE</code><a name="index-PARAM_005fSTRING_005fNOESCAPE-2650"></a><dd>The value is a string. When the user modifies the string, escapes are
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passed through untranslated.
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<br><dt><code>PARAM_OPTIONAL_FILENAME</code><a name="index-PARAM_005fOPTIONAL_005fFILENAME-2651"></a><dd>The value is a either a filename (a string), or <code>#f</code>.
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<br><dt><code>PARAM_FILENAME</code><a name="index-PARAM_005fFILENAME-2652"></a><dd>The value is a filename. This is just like
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<code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion.
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<br><dt><code>PARAM_ENUM</code><a name="index-PARAM_005fENUM-2653"></a><dd>The value is a string, which must be one of a collection of string
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constants provided when the parameter is created.
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</dl>
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<div class="footnote">
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<hr>
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<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Note that <span class="sc">gdb</span> parameters must not be confused with
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Guile’s parameter objects (see <a href="../guile/Parameters.html#Parameters">Parameters</a>).</p>
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