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| <h5 class="subsubsection">23.3.3.9 Selecting Guile Pretty-Printers</h5> |
| |
| <p><a name="index-selecting-guile-pretty_002dprinters-2604"></a> |
| There are three sets of pretty-printers that <span class="sc">gdb</span> searches: |
| |
| <ul> |
| <li>Per-objfile list of pretty-printers (see <a href="Objfiles-In-Guile.html#Objfiles-In-Guile">Objfiles In Guile</a>). |
| <li>Per-progspace list of pretty-printers (see <a href="Progspaces-In-Guile.html#Progspaces-In-Guile">Progspaces In Guile</a>). |
| <li>The global list of pretty-printers (see <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API">Guile Pretty Printing API</a>). |
| These printers are available when debugging any inferior. |
| </ul> |
| |
| <p>Pretty-printer lookup is done by passing the value to be printed to the |
| lookup function of each enabled object in turn. |
| Lookup stops when a lookup function returns a non-<code>#f</code> value |
| or when the list is exhausted. |
| Lookup functions must return either a <code><gdb:pretty-printer-worker></code> |
| object or <code>#f</code>. Otherwise an exception is thrown. |
| |
| <p><span class="sc">gdb</span> first checks the result of <code>objfile-pretty-printers</code> |
| of each <code><gdb:objfile></code> in the current program space and iteratively |
| calls each enabled lookup function in the list for that <code><gdb:objfile></code> |
| until a non-<code>#f</code> object is returned. |
| If no pretty-printer is found in the objfile lists, <span class="sc">gdb</span> then |
| searches the result of <code>progspace-pretty-printers</code> of the current |
| program space, calling each enabled function until a non-<code>#f</code> object |
| is returned. |
| After these lists have been exhausted, it tries the global pretty-printers |
| list, obtained with <code>pretty-printers</code>, again calling each enabled |
| function until a non-<code>#f</code> object is returned. |
| |
| <p>The order in which the objfiles are searched is not specified. For a |
| given list, functions are always invoked from the head of the list, |
| and iterated over sequentially until the end of the list, or a |
| <code><gdb:pretty-printer-worker></code> object is returned. |
| |
| <p>For various reasons a pretty-printer may not work. |
| For example, the underlying data structure may have changed and |
| the pretty-printer is out of date. |
| |
| <p>The consequences of a broken pretty-printer are severe enough that |
| <span class="sc">gdb</span> provides support for enabling and disabling individual |
| printers. For example, if <code>print frame-arguments</code> is on, |
| a backtrace can become highly illegible if any argument is printed |
| with a broken printer. |
| |
| <p>Pretty-printers are enabled and disabled from Scheme by calling |
| <code>set-pretty-printer-enabled!</code>. |
| See <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API">Guile Pretty Printing API</a>. |
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