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