/usr/lib/swi-prolog/doc/Manual/hooks.html

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<h2 id="sec:hooks"><a id="sec:2.12"><span class="sec-nr">2.12</span> <span class="sec-title">An 
overview of hook predicates</span></a></h2>

<a id="sec:hooks"></a>

<p><a id="idx:hooks:137"></a>SWI-Prolog provides a large number of 
hooks, mainly to control handling messages, debugging, startup, 
shut-down, macro-expansion, etc. Below is a summary of all defined hooks 
with an indication of their portability.

<p>
<ul class="latex">
<li><i>portray/1</i><br>
Hook into <a id="idx:writeterm3:138"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a> 
to alter the way terms are printed (ISO).
<li><i>message_hook/3</i><br>
Hook into <a id="idx:printmessage2:139"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a> 
to alter the way system messages are printed (Quintus/SICStus).
<li><i>message_property/2</i><br>
Hook into <a id="idx:printmessage2:140"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a> 
that defines prefix, output stream, color, etc.
<li><i>library_directory/1</i><br>
Hook into <a id="idx:absolutefilename3:141"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a> 
to define new library directories (most Prolog systems).
<li><i>file_search_path/2</i><br>
Hook into <a id="idx:absolutefilename3:142"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a> 
to define new search paths (Quintus/SICStus).
<li><i>term_expansion/2</i><br>
Hook into <a id="idx:loadfiles2:143"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a> 
to modify read terms before they are compiled (macro-processing) (most 
Prolog systems).
<li><i>goal_expansion/2</i><br>
Same as <a id="idx:termexpansion2:144"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a> 
for individual goals (SICStus).
<li><i>prolog_load_file/2</i><br>
Hook into <a id="idx:loadfiles2:145"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a> 
to load other data formats for Prolog sources from `non-file' resources. 
The <a id="idx:loadfiles2:146"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a> 
predicate is the ancestor of <a id="idx:consult1:147"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>, <a id="idx:usemodule1:148"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>, 
etc.
<li><i>prolog_edit:locate/3</i><br>
Hook into <a id="idx:edit1:149"></a><a class="pred" href="edit.html#edit/1">edit/1</a> 
to locate objects (SWI).
<li><i>prolog_edit:edit_source/1</i><br>
Hook into <a id="idx:edit1:150"></a><a class="pred" href="edit.html#edit/1">edit/1</a> 
to call an internal editor (SWI).
<li><i>prolog_edit:edit_command/2</i><br>
Hook into <a id="idx:edit1:151"></a><a class="pred" href="edit.html#edit/1">edit/1</a> 
to define the external editor to use (SWI).
<li><i>prolog_list_goal/1</i><br>
Hook into the tracer to list the code associated to a particular goal 
(SWI).
<li><i>prolog_trace_interception/4</i><br>
Hook into the tracer to handle trace events (SWI).
<li><i>prolog:debug_control_hook/1</i><br>
Hook in <a id="idx:spy1:152"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>, <a id="idx:nospy1:153"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>, <a id="idx:nospyall0:154"></a><a class="pred" href="debugger.html#nospyall/0">nospyall/0</a> 
and <a id="idx:debugging0:155"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a> 
to extend these control predicates to higher-level libraries.
<li><i>prolog:help_hook/1</i><br>
Hook in <a id="idx:help0:156"></a><a class="pred" href="help.html#help/0">help/0</a>, <a id="idx:help1:157"></a><a class="pred" href="help.html#help/1">help/1</a> 
and <a id="idx:apropos1:158"></a><a class="pred" href="help.html#apropos/1">apropos/1</a> 
to extend the help system.
<li><i>resource/3</i><br>
Define a new resource (not really a hook, but similar) (SWI).
<li><i>exception/3</i><br>
Old attempt to a generic hook mechanism. Handles undefined predicates 
(SWI).
<li><i>attr_unify_hook/2</i><br>
Unification hook for attributed variables. Can be defined in any module. 
See <a class="sec" href="attvar.html">section 6.1</a> for details.
</ul>

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swi-prolog-nox 6.6.6-5 / usr / lib / swi-prolog / doc / Manual / hooks.html
