190 lines
9.7 KiB
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190 lines
9.7 KiB
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<html lang="en">
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<title>Guile Pretty Printing API - Debugging with GDB</title>
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<meta name="description" content="Debugging with GDB">
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<link rel="up" href="Guile-API.html#Guile-API" title="Guile API">
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<link rel="prev" href="Types-In-Guile.html#Types-In-Guile" title="Types In Guile">
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<body>
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<div class="node">
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<a name="Guile-Pretty-Printing-API"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Selecting-Guile-Pretty_002dPrinters.html#Selecting-Guile-Pretty_002dPrinters">Selecting Guile Pretty-Printers</a>,
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Previous: <a rel="previous" accesskey="p" href="Types-In-Guile.html#Types-In-Guile">Types 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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<hr>
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</div>
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<h5 class="subsubsection">23.3.3.8 Guile Pretty Printing API</h5>
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<p><a name="index-guile-pretty-printing-api-2595"></a>
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An example output is provided (see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>).
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<p>A pretty-printer is represented by an object of type <gdb:pretty-printer>.
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Pretty-printer objects are created with <code>make-pretty-printer</code>.
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<p>The following pretty-printer-related procedures are provided by the
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<code>(gdb)</code> module:
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<div class="defun">
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— Scheme Procedure: <b>make-pretty-printer</b><var> name lookup-function<a name="index-make_002dpretty_002dprinter-2596"></a></var><br>
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<blockquote><p>Return a <code><gdb:pretty-printer></code> object named <var>name</var>.
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<p><var>lookup-function</var> is a function of one parameter: the value to
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be printed. If the value is handled by this pretty-printer, then
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<var>lookup-function</var> returns an object of type
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<gdb:pretty-printer-worker> to perform the actual pretty-printing.
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Otherwise <var>lookup-function</var> returns <code>#f</code>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>pretty-printer?</b><var> object<a name="index-pretty_002dprinter_003f-2597"></a></var><br>
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<blockquote><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:pretty-printer></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>pretty-printer-enabled?</b><var> pretty-printer<a name="index-pretty_002dprinter_002denabled_003f-2598"></a></var><br>
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<blockquote><p>Return <code>#t</code> if <var>pretty-printer</var> is enabled.
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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>set-pretty-printer-enabled!</b><var> pretty-printer flag<a name="index-set_002dpretty_002dprinter_002denabled_0021-2599"></a></var><br>
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<blockquote><p>Set the enabled flag of <var>pretty-printer</var> to <var>flag</var>.
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The value returned is unspecified.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>pretty-printers</b><var><a name="index-pretty_002dprinters-2600"></a></var><br>
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<blockquote><p>Return the list of global pretty-printers.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>set-pretty-printers!</b><var> pretty-printers<a name="index-set_002dpretty_002dprinters_0021-2601"></a></var><br>
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<blockquote><p>Set the list of global pretty-printers to <var>pretty-printers</var>.
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The value returned is unspecified.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>make-pretty-printer-worker</b><var> display-hint to-string children<a name="index-make_002dpretty_002dprinter_002dworker-2602"></a></var><br>
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<blockquote><p>Return an object of type <code><gdb:pretty-printer-worker></code>.
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<p>This function takes three parameters:
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<dl>
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<dt>‘<samp><span class="samp">display-hint</span></samp>’<dd><var>display-hint</var> provides a hint to <span class="sc">gdb</span> or <span class="sc">gdb</span>
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front end via MI to change the formatting of the value being printed.
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The value must be a string or <code>#f</code> (meaning there is no hint).
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Several values for <var>display-hint</var>
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are predefined by <span class="sc">gdb</span>:
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<dl>
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<dt>‘<samp><span class="samp">array</span></samp>’<dd>Indicate that the object being printed is “array-like”. The CLI
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uses this to respect parameters such as <code>set print elements</code> and
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<code>set print array</code>.
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<br><dt>‘<samp><span class="samp">map</span></samp>’<dd>Indicate that the object being printed is “map-like”, and that the
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children of this value can be assumed to alternate between keys and
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values.
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<br><dt>‘<samp><span class="samp">string</span></samp>’<dd>Indicate that the object being printed is “string-like”. If the
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printer's <code>to-string</code> function returns a Guile string of some
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kind, then <span class="sc">gdb</span> will call its internal language-specific
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string-printing function to format the string. For the CLI this means
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adding quotation marks, possibly escaping some characters, respecting
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<code>set print elements</code>, and the like.
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</dl>
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<br><dt>‘<samp><span class="samp">to-string</span></samp>’<dd><var>to-string</var> is either a function of one parameter, the
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<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>.
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<p>When printing from the CLI, if the <code>to-string</code> method exists,
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then <span class="sc">gdb</span> will prepend its result to the values returned by
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<code>children</code>. Exactly how this formatting is done is dependent on
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the display hint, and may change as more hints are added. Also,
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depending on the print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>), the CLI may
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print just the result of <code>to-string</code> in a stack trace, omitting
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the result of <code>children</code>.
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<p>If this method returns a string, it is printed verbatim.
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<p>Otherwise, if this method returns an instance of <code><gdb:value></code>,
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then <span class="sc">gdb</span> prints this value. This may result in a call to
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another pretty-printer.
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<p>If instead the method returns a Guile value which is convertible to a
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<code><gdb:value></code>, then <span class="sc">gdb</span> performs the conversion and prints
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the resulting value. Again, this may result in a call to another
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pretty-printer. Guile scalars (integers, floats, and booleans) and
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strings are convertible to <code><gdb:value></code>; other types are not.
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<p>Finally, if this method returns <code>#f</code> then no further operations
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are peformed in this method and nothing is printed.
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<p>If the result is not one of these types, an exception is raised.
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<p><var>to-string</var> may also be <code>#f</code> in which case it is left to
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<var>children</var> to print the value.
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<br><dt>‘<samp><span class="samp">children</span></samp>’<dd><var>children</var> is either a function of one parameter, the
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<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>.
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<p><span class="sc">gdb</span> will call this function on a pretty-printer to compute the
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children of the pretty-printer's value.
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<p>This function must return a <gdb:iterator> object.
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Each item returned by the iterator must be a tuple holding
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two elements. The first element is the “name” of the child; the
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second element is the child's value. The value can be any Guile
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object which is convertible to a <span class="sc">gdb</span> value.
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<p>If <var>children</var> is <code>#f</code>, <span class="sc">gdb</span> will act
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as though the value has no children.
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</dl>
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</p></blockquote></div>
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<p><span class="sc">gdb</span> provides a function which can be used to look up the
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default pretty-printer for a <code><gdb:value></code>:
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<div class="defun">
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— Scheme Procedure: <b>default-visualizer</b><var> value<a name="index-default_002dvisualizer-2603"></a></var><br>
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<blockquote><p>This function takes a <code><gdb:value></code> object as an argument. If a
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pretty-printer for this value exists, then it is returned. If no such
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printer exists, then this returns <code>#f</code>.
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</p></blockquote></div>
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</body></html>
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