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 <a name="Parameters-In-Guile"></a>
 <div class="header">
 <p>
 Next: <a href="Progspaces-In-Guile.html#Progspaces-In-Guile" accesskey="n" rel="next">Progspaces In Guile</a>, Previous: <a href="Commands-In-Guile.html#Commands-In-Guile" accesskey="p" rel="prev">Commands In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Parameters-In-Guile-1"></a>
 <h4 class="subsubsection">23.3.3.12 Parameters In Guile</h4>

 <a name="index-parameters-in-guile"></a>
 <a name="index-guile-parameters"></a>
 <a name="index-Parameter-1"></a>
 <p>You can implement new <small>GDB</small> <em>parameters</em> using Guile
 <a name="DOCF17" href="#FOOT17"><sup>17</sup></a>.
 </p>
 <p>There are many parameters that already exist and can be set in
 <small>GDB</small>.  Two examples are: <code>set follow-fork</code> and
 <code>set charset</code>.  Setting these parameters influences certain
 behavior in <small>GDB</small>.  Similarly, you can define parameters that
 can be used to influence behavior in custom Guile scripts and commands.
 </p>
 <p>A new parameter is defined with the <code>make-parameter</code> Guile function,
 and added to <small>GDB</small> with the <code>register-parameter!</code> Guile function.
 This two-step approach is taken to separate out the side-effect of adding
 the parameter to <small>GDB</small> from <code>make-parameter</code>.
 </p>
 <p>Parameters are exposed to the user via the <code>set</code> and
 <code>show</code> commands.  See <a href="Help.html#Help">Help</a>.
 </p>
 <dl>
 <dt><a name="index-_0028make_002dparameter"></a>Scheme Procedure: <strong>(make-parameter</strong> <em>name <span class="roman">[</span>#:command-class command-class<span class="roman">]</span> <span class="roman">[</span>#:parameter-type parameter-type] <span class="roman">[</span>#:enum-list enum-list<span class="roman">]</span> <span class="roman">[</span>#:set-func set-func] <span class="roman">[</span>#:show-func show-func] <span class="roman">[</span>#:doc doc] <span class="roman">[</span>#:set-doc set-doc] <span class="roman">[</span>#:show-doc show-doc] <span class="roman">[</span>#:initial-value initial-value])</em></dt>
 <dd>
 <p>The argument <var>name</var> is the name of the new parameter.  If <var>name</var>
 consists of multiple words, then the initial words are looked for as prefix
 parameters.  An example of this can be illustrated with the
 <code>set print</code> set of parameters.  If <var>name</var> is
 <code>print foo</code>, then <code>print</code> will be searched as the prefix
 parameter.  In this case the parameter can subsequently be accessed in
 <small>GDB</small> as <code>set print foo</code>.
 If <var>name</var> consists of multiple words, and no prefix parameter group
 can be found, an exception is raised.
 </p>
 <p>The result is the <code>&lt;gdb:parameter&gt;</code> object representing the parameter.
 The parameter is not usable until it has been registered with <small>GDB</small>
 with <code>register-parameter!</code>.
 </p>
 <p>The rest of the arguments are optional.
 </p>
 <p>The argument <var>command-class</var> should be one of the &lsquo;<samp>COMMAND_</samp>&rsquo; constants
 (see <a href="Commands-In-Guile.html#Commands-In-Guile">Commands In Guile</a>).  This argument tells <small>GDB</small> how to
 categorize the new parameter in the help system.
 The default is <code>COMMAND_NONE</code>.
 </p>
 <p>The argument <var>parameter-type</var> should be one of the &lsquo;<samp>PARAM_</samp>&rsquo; constants
 defined below.  This argument tells <small>GDB</small> the type of the new
 parameter; this information is used for input validation and
 completion.  The default is <code>PARAM_BOOLEAN</code>.
 </p>
 <p>If <var>parameter-type</var> is <code>PARAM_ENUM</code>, then
 <var>enum-list</var> must be a list of strings.  These strings
 represent the possible values for the parameter.
 </p>
 <p>If <var>parameter-type</var> is not <code>PARAM_ENUM</code>, then the presence
 of <var>enum-list</var> will cause an exception to be thrown.
 </p>
 <p>The argument <var>set-func</var> is a function of one argument: <var>self</var> which
 is the <code>&lt;gdb:parameter&gt;</code> object representing the parameter.
 <small>GDB</small> will call this function when a <var>parameter</var>&rsquo;s value has
 been changed via the <code>set</code> API (for example, <kbd>set foo off</kbd>).
 The value of the parameter has already been set to the new value.
 This function must return a string to be displayed to the user.
 <small>GDB</small> will add a trailing newline if the string is non-empty.
 <small>GDB</small> generally doesn&rsquo;t print anything when a parameter is set,
 thus typically this function should return &lsquo;<samp>&quot;&quot;</samp>&rsquo;.
 A non-empty string result should typically be used for displaying warnings
 and errors.
 </p>
 <p>The argument <var>show-func</var> is a function of two arguments: <var>self</var> which
 is the <code>&lt;gdb:parameter&gt;</code> object representing the parameter, and
 <var>svalue</var> which is the string representation of the current value.
 <small>GDB</small> will call this function when a <var>parameter</var>&rsquo;s
 <code>show</code> API has been invoked (for example, <kbd>show foo</kbd>).
 This function must return a string, and will be displayed to the user.
 <small>GDB</small> will add a trailing newline.
 </p>
 <p>The argument <var>doc</var> is the help text for the new parameter.
 If there is no documentation string, a default value is used.
 </p>
 <p>The argument <var>set-doc</var> is the help text for this parameter&rsquo;s
 <code>set</code> command.
 </p>
 <p>The argument <var>show-doc</var> is the help text for this parameter&rsquo;s
 <code>show</code> command.
 </p>
 <p>The argument <var>initial-value</var> specifies the initial value of the parameter.
 If it is a function, it takes one parameter, the <code>&lt;gdb:parameter&gt;</code>
 object and its result is used as the initial value of the parameter.
 The initial value must be valid for the parameter type,
 otherwise an exception is thrown.
 </p></dd></dl>

 <dl>
 <dt><a name="index-register_002dparameter_0021"></a>Scheme Procedure: <strong>register-parameter!</strong> <em>parameter</em></dt>
 <dd><p>Add <var>parameter</var>, a <code>&lt;gdb:parameter&gt;</code> object, to <small>GDB</small>&rsquo;s
 list of parameters.
 It is an error to register a parameter more than once.
 The result is unspecified.
 </p></dd></dl>

 <dl>
 <dt><a name="index-parameter_003f"></a>Scheme Procedure: <strong>parameter?</strong> <em>object</em></dt>
 <dd><p>Return <code>#t</code> if <var>object</var> is a <code>&lt;gdb:parameter&gt;</code> object.
 Otherwise return <code>#f</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-parameter_002dvalue"></a>Scheme Procedure: <strong>parameter-value</strong> <em>parameter</em></dt>
 <dd><p>Return the value of <var>parameter</var> which may either be
 a <code>&lt;gdb:parameter&gt;</code> object or a string naming the parameter.
 </p></dd></dl>

 <dl>
 <dt><a name="index-set_002dparameter_002dvalue_0021"></a>Scheme Procedure: <strong>set-parameter-value!</strong> <em>parameter new-value</em></dt>
 <dd><p>Assign <var>parameter</var> the value of <var>new-value</var>.
 The argument <var>parameter</var> must be an object of type <code>&lt;gdb:parameter&gt;</code>.
 <small>GDB</small> does validation when assignments are made.
 </p></dd></dl>

 <p>When a new parameter is defined, its type must be specified.  The
 available types are represented by constants defined in the <code>gdb</code>
 module:
 </p>
 <dl compact="compact">
 <dt><code>PARAM_BOOLEAN</code>
 <a name="index-PARAM_005fBOOLEAN-1"></a>
 </dt>
 <dd><p>The value is a plain boolean.  The Guile boolean values, <code>#t</code>
 and <code>#f</code> are the only valid values.
 </p>
 </dd>
 <dt><code>PARAM_AUTO_BOOLEAN</code>
 <a name="index-PARAM_005fAUTO_005fBOOLEAN-1"></a>
 </dt>
 <dd><p>The value has three possible states: true, false, and &lsquo;<samp>auto</samp>&rsquo;.  In
 Guile, true and false are represented using boolean constants, and
 &lsquo;<samp>auto</samp>&rsquo; is represented using <code>#:auto</code>.
 </p>
 </dd>
 <dt><code>PARAM_UINTEGER</code>
 <a name="index-PARAM_005fUINTEGER-1"></a>
 </dt>
 <dd><p>The value is an unsigned integer.  The value of 0 should be
 interpreted to mean &ldquo;unlimited&rdquo;.
 </p>
 </dd>
 <dt><code>PARAM_ZINTEGER</code>
 <a name="index-PARAM_005fZINTEGER-1"></a>
 </dt>
 <dd><p>The value is an integer.
 </p>
 </dd>
 <dt><code>PARAM_ZUINTEGER</code>
 <a name="index-PARAM_005fZUINTEGER"></a>
 </dt>
 <dd><p>The value is an unsigned integer.
 </p>
 </dd>
 <dt><code>PARAM_ZUINTEGER_UNLIMITED</code>
 <a name="index-PARAM_005fZUINTEGER_005fUNLIMITED"></a>
 </dt>
 <dd><p>The value is an integer in the range &lsquo;<samp>[0, INT_MAX]</samp>&rsquo;.
 A value of &lsquo;<samp>-1</samp>&rsquo; means &ldquo;unlimited&rdquo;, and other negative
 numbers are not allowed.
 </p>
 </dd>
 <dt><code>PARAM_STRING</code>
 <a name="index-PARAM_005fSTRING-1"></a>
 </dt>
 <dd><p>The value is a string.  When the user modifies the string, any escape
 sequences, such as &lsquo;<samp>\t</samp>&rsquo;, &lsquo;<samp>\f</samp>&rsquo;, and octal escapes, are
 translated into corresponding characters and encoded into the current
 host charset.
 </p>
 </dd>
 <dt><code>PARAM_STRING_NOESCAPE</code>
 <a name="index-PARAM_005fSTRING_005fNOESCAPE-1"></a>
 </dt>
 <dd><p>The value is a string.  When the user modifies the string, escapes are
 passed through untranslated.
 </p>
 </dd>
 <dt><code>PARAM_OPTIONAL_FILENAME</code>
 <a name="index-PARAM_005fOPTIONAL_005fFILENAME-1"></a>
 </dt>
 <dd><p>The value is a either a filename (a string), or <code>#f</code>.
 </p>
 </dd>
 <dt><code>PARAM_FILENAME</code>
 <a name="index-PARAM_005fFILENAME-1"></a>
 </dt>
 <dd><p>The value is a filename.  This is just like
 <code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion.
 </p>
 </dd>
 <dt><code>PARAM_ENUM</code>
 <a name="index-PARAM_005fENUM-1"></a>
 </dt>
 <dd><p>The value is a string, which must be one of a collection of string
 constants provided when the parameter is created.
 </p></dd>
 </dl>

 <div class="footnote">
 <hr>
 <h4 class="footnotes-heading">Footnotes</h4>

 <h3><a name="FOOT17" href="#DOCF17">(17)</a></h3>
 <p>Note that <small>GDB</small> parameters must not be confused with
 Guileâs parameter objects (see <a href="http://www.gnu.org/software/guile/manual/html_node/Parameters.html#Parameters">Parameters</a> in <cite>GNU Guile
 Reference Manual</cite>).</p>
 </div>
 <hr>
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 <p>
 Next: <a href="Progspaces-In-Guile.html#Progspaces-In-Guile" accesskey="n" rel="next">Progspaces In Guile</a>, Previous: <a href="Commands-In-Guile.html#Commands-In-Guile" accesskey="p" rel="prev">Commands In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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	<a name="Parameters-In-Guile"></a>
	<div class="header">
	<p>
	Next: <a href="Progspaces-In-Guile.html#Progspaces-In-Guile" accesskey="n" rel="next">Progspaces In Guile</a>, Previous: <a href="Commands-In-Guile.html#Commands-In-Guile" accesskey="p" rel="prev">Commands In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Parameters-In-Guile-1"></a>
	<h4 class="subsubsection">23.3.3.12 Parameters In Guile</h4>

	<a name="index-parameters-in-guile"></a>
	<a name="index-guile-parameters"></a>
	<a name="index-Parameter-1"></a>
	<p>You can implement new <small>GDB</small> <em>parameters</em> using Guile
	<a name="DOCF17" href="#FOOT17"><sup>17</sup></a>.
	</p>
	<p>There are many parameters that already exist and can be set in
	<small>GDB</small>. Two examples are: <code>set follow-fork</code> and
	<code>set charset</code>. Setting these parameters influences certain
	behavior in <small>GDB</small>. Similarly, you can define parameters that
	can be used to influence behavior in custom Guile scripts and commands.
	</p>
	<p>A new parameter is defined with the <code>make-parameter</code> Guile function,
	and added to <small>GDB</small> with the <code>register-parameter!</code> Guile function.
	This two-step approach is taken to separate out the side-effect of adding
	the parameter to <small>GDB</small> from <code>make-parameter</code>.
	</p>
	<p>Parameters are exposed to the user via the <code>set</code> and
	<code>show</code> commands. See <a href="Help.html#Help">Help</a>.
	</p>
	<dl>
	<dt><a name="index-_0028make_002dparameter"></a>Scheme Procedure: <strong>(make-parameter</strong> <em>name <span class="roman">[</span>#:command-class command-class<span class="roman">]</span> <span class="roman">[</span>#:parameter-type parameter-type] <span class="roman">[</span>#:enum-list enum-list<span class="roman">]</span> <span class="roman">[</span>#:set-func set-func] <span class="roman">[</span>#:show-func show-func] <span class="roman">[</span>#:doc doc] <span class="roman">[</span>#:set-doc set-doc] <span class="roman">[</span>#:show-doc show-doc] <span class="roman">[</span>#:initial-value initial-value])</em></dt>
	<dd>
	<p>The argument <var>name</var> is the name of the new parameter. If <var>name</var>
	consists of multiple words, then the initial words are looked for as prefix
	parameters. An example of this can be illustrated with the
	<code>set print</code> set of parameters. If <var>name</var> is
	<code>print foo</code>, then <code>print</code> will be searched as the prefix
	parameter. In this case the parameter can subsequently be accessed in
	<small>GDB</small> as <code>set print foo</code>.
	If <var>name</var> consists of multiple words, and no prefix parameter group
	can be found, an exception is raised.
	</p>
	<p>The result is the <code><gdb:parameter></code> object representing the parameter.
	The parameter is not usable until it has been registered with <small>GDB</small>
	with <code>register-parameter!</code>.
	</p>
	<p>The rest of the arguments are optional.
	</p>
	<p>The argument <var>command-class</var> should be one of the ‘<samp>COMMAND_</samp>’ constants
	(see <a href="Commands-In-Guile.html#Commands-In-Guile">Commands In Guile</a>). This argument tells <small>GDB</small> how to
	categorize the new parameter in the help system.
	The default is <code>COMMAND_NONE</code>.
	</p>
	<p>The argument <var>parameter-type</var> should be one of the ‘<samp>PARAM_</samp>’ constants
	defined below. This argument tells <small>GDB</small> the type of the new
	parameter; this information is used for input validation and
	completion. The default is <code>PARAM_BOOLEAN</code>.
	</p>
	<p>If <var>parameter-type</var> is <code>PARAM_ENUM</code>, then
	<var>enum-list</var> must be a list of strings. These strings
	represent the possible values for the parameter.
	</p>
	<p>If <var>parameter-type</var> is not <code>PARAM_ENUM</code>, then the presence
	of <var>enum-list</var> will cause an exception to be thrown.
	</p>
	<p>The argument <var>set-func</var> is a function of one argument: <var>self</var> which
	is the <code><gdb:parameter></code> object representing the parameter.
	<small>GDB</small> will call this function when a <var>parameter</var>’s value has
	been changed via the <code>set</code> API (for example, <kbd>set foo off</kbd>).
	The value of the parameter has already been set to the new value.
	This function must return a string to be displayed to the user.
	<small>GDB</small> will add a trailing newline if the string is non-empty.
	<small>GDB</small> generally doesn’t print anything when a parameter is set,
	thus typically this function should return ‘<samp>""</samp>’.
	A non-empty string result should typically be used for displaying warnings
	and errors.
	</p>
	<p>The argument <var>show-func</var> is a function of two arguments: <var>self</var> which
	is the <code><gdb:parameter></code> object representing the parameter, and
	<var>svalue</var> which is the string representation of the current value.
	<small>GDB</small> will call this function when a <var>parameter</var>’s
	<code>show</code> API has been invoked (for example, <kbd>show foo</kbd>).
	This function must return a string, and will be displayed to the user.
	<small>GDB</small> will add a trailing newline.
	</p>
	<p>The argument <var>doc</var> is the help text for the new parameter.
	If there is no documentation string, a default value is used.
	</p>
	<p>The argument <var>set-doc</var> is the help text for this parameter’s
	<code>set</code> command.
	</p>
	<p>The argument <var>show-doc</var> is the help text for this parameter’s
	<code>show</code> command.
	</p>
	<p>The argument <var>initial-value</var> specifies the initial value of the parameter.
	If it is a function, it takes one parameter, the <code><gdb:parameter></code>
	object and its result is used as the initial value of the parameter.
	The initial value must be valid for the parameter type,
	otherwise an exception is thrown.
	</p></dd></dl>

	<dl>
	<dt><a name="index-register_002dparameter_0021"></a>Scheme Procedure: <strong>register-parameter!</strong> <em>parameter</em></dt>
	<dd><p>Add <var>parameter</var>, a <code><gdb:parameter></code> object, to <small>GDB</small>’s
	list of parameters.
	It is an error to register a parameter more than once.
	The result is unspecified.
	</p></dd></dl>

	<dl>
	<dt><a name="index-parameter_003f"></a>Scheme Procedure: <strong>parameter?</strong> <em>object</em></dt>
	<dd><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:parameter></code> object.
	Otherwise return <code>#f</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-parameter_002dvalue"></a>Scheme Procedure: <strong>parameter-value</strong> <em>parameter</em></dt>
	<dd><p>Return the value of <var>parameter</var> which may either be
	a <code><gdb:parameter></code> object or a string naming the parameter.
	</p></dd></dl>

	<dl>
	<dt><a name="index-set_002dparameter_002dvalue_0021"></a>Scheme Procedure: <strong>set-parameter-value!</strong> <em>parameter new-value</em></dt>
	<dd><p>Assign <var>parameter</var> the value of <var>new-value</var>.
	The argument <var>parameter</var> must be an object of type <code><gdb:parameter></code>.
	<small>GDB</small> does validation when assignments are made.
	</p></dd></dl>

	<p>When a new parameter is defined, its type must be specified. The
	available types are represented by constants defined in the <code>gdb</code>
	module:
	</p>
	<dl compact="compact">
	<dt><code>PARAM_BOOLEAN</code>
	<a name="index-PARAM_005fBOOLEAN-1"></a>
	</dt>
	<dd><p>The value is a plain boolean. The Guile boolean values, <code>#t</code>
	and <code>#f</code> are the only valid values.
	</p>
	</dd>
	<dt><code>PARAM_AUTO_BOOLEAN</code>
	<a name="index-PARAM_005fAUTO_005fBOOLEAN-1"></a>
	</dt>
	<dd><p>The value has three possible states: true, false, and ‘<samp>auto</samp>’. In
	Guile, true and false are represented using boolean constants, and
	‘<samp>auto</samp>’ is represented using <code>#:auto</code>.
	</p>
	</dd>
	<dt><code>PARAM_UINTEGER</code>
	<a name="index-PARAM_005fUINTEGER-1"></a>
	</dt>
	<dd><p>The value is an unsigned integer. The value of 0 should be
	interpreted to mean “unlimited”.
	</p>
	</dd>
	<dt><code>PARAM_ZINTEGER</code>
	<a name="index-PARAM_005fZINTEGER-1"></a>
	</dt>
	<dd><p>The value is an integer.
	</p>
	</dd>
	<dt><code>PARAM_ZUINTEGER</code>
	<a name="index-PARAM_005fZUINTEGER"></a>
	</dt>
	<dd><p>The value is an unsigned integer.
	</p>
	</dd>
	<dt><code>PARAM_ZUINTEGER_UNLIMITED</code>
	<a name="index-PARAM_005fZUINTEGER_005fUNLIMITED"></a>
	</dt>
	<dd><p>The value is an integer in the range ‘<samp>[0, INT_MAX]</samp>’.
	A value of ‘<samp>-1</samp>’ means “unlimited”, and other negative
	numbers are not allowed.
	</p>
	</dd>
	<dt><code>PARAM_STRING</code>
	<a name="index-PARAM_005fSTRING-1"></a>
	</dt>
	<dd><p>The value is a string. When the user modifies the string, any escape
	sequences, such as ‘<samp>\t</samp>’, ‘<samp>\f</samp>’, and octal escapes, are
	translated into corresponding characters and encoded into the current
	host charset.
	</p>
	</dd>
	<dt><code>PARAM_STRING_NOESCAPE</code>
	<a name="index-PARAM_005fSTRING_005fNOESCAPE-1"></a>
	</dt>
	<dd><p>The value is a string. When the user modifies the string, escapes are
	passed through untranslated.
	</p>
	</dd>
	<dt><code>PARAM_OPTIONAL_FILENAME</code>
	<a name="index-PARAM_005fOPTIONAL_005fFILENAME-1"></a>
	</dt>
	<dd><p>The value is a either a filename (a string), or <code>#f</code>.
	</p>
	</dd>
	<dt><code>PARAM_FILENAME</code>
	<a name="index-PARAM_005fFILENAME-1"></a>
	</dt>
	<dd><p>The value is a filename. This is just like
	<code>PARAM_STRING_NOESCAPE</code>, but uses file names for completion.
	</p>
	</dd>
	<dt><code>PARAM_ENUM</code>
	<a name="index-PARAM_005fENUM-1"></a>
	</dt>
	<dd><p>The value is a string, which must be one of a collection of string
	constants provided when the parameter is created.
	</p></dd>
	</dl>

	<div class="footnote">
	<hr>
	<h4 class="footnotes-heading">Footnotes</h4>

	<h3><a name="FOOT17" href="#DOCF17">(17)</a></h3>
	<p>Note that <small>GDB</small> parameters must not be confused with
	Guileâs parameter objects (see <a href="http://www.gnu.org/software/guile/manual/html_node/Parameters.html#Parameters">Parameters</a> in <cite>GNU Guile
	Reference Manual</cite>).</p>
	</div>
	<hr>
	<div class="header">
	<p>
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