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

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<h2 id="sec:toplevel"><a id="sec:4.36"><span class="sec-nr">4.36</span> <span class="sec-title">User 
Top-level Manipulation</span></a></h2>

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

<dl class="latex">
<dt class="pubdef"><a id="break/0"><strong>break</strong></a></dt>
<dd class="defbody">
Recursively start a new Prolog top level. This Prolog top level has its 
own stacks, but shares the heap with all break environments and the top 
level. Debugging is switched off on entering a break and restored on 
leaving one. The break environment is terminated by typing the system's 
end-of-file character (control-D). If the
<strong>-t</strong> <var>toplevel</var> command line option is given, 
this goal is started instead of entering the default interactive top 
level (<a id="idx:prolog0:1329"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).</dd>
<dt class="pubdef"><a id="abort/0"><strong>abort</strong></a></dt>
<dd class="defbody">
Abort the Prolog execution and restart the top level. If the
<strong>-t</strong> <var>toplevel</var> command line option is given, 
this goal is started instead of entering the default interactive top 
level.

<p>Aborting is implemented by throwing the reserved exception
<code>'$aborted'</code>. This exception can be caught using <a id="idx:catch3:1330"></a><a class="pred" href="exception.html#catch/3">catch/3</a>, 
but the recovery goal is wrapped with a predicate that prunes the choice 
points of the recovery goal (i.e., as <a id="idx:once1:1331"></a><a class="pred" href="metacall.html#once/1">once/1</a>) 
and re-throws the exception. This is illustrated in the example below, 
where we press control-C and `a'.

<pre class="code">
?- catch((repeat,fail), E, true).
^CAction (h for help) ? abort
% Execution Aborted
</pre>

</dd>
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="halt/0"><strong>halt</strong></a></dt>
<dd class="defbody">
Terminate Prolog execution. This is the same as <code>halt(0)</code>. 
See
<a id="idx:halt1:1332"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a> 
for details.</dd>
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="halt/1"><strong>halt</strong>(<var>+Status</var>)</a></dt>
<dd class="defbody">
Terminate Prolog execution with <var>Status</var>. This predicate calls
<a class="func" href="foreigninclude.html#PL_halt()">PL_halt()</a> which 
preforms the following steps:

<p>
<ol class="latex">
<li>Set the Prolog flag <a class="flag" href="flags.html#flag:exit_status">exit_status</a> 
to <var>Status</var>.

<p>
<li>Call all hooks registered using <a id="idx:athalt1:1333"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>. 
If <var>Status</var> equals 0 (zero), any of these hooks calls <a id="idx:cancelhalt1:1334"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>, 
termination is cancelled.

<p>
<li>Call all hooks registered using <b>PL_at_halt()</b>. In the future, 
if any of these hooks returns non-zero, termination will be cancelled. 
Currently, this only prints a warning.

<p>
<li>Perform the following system cleanup actions:

<p>
<ul class="latex">
<li>Cancel all threads, calling <a id="idx:threadatexit1:1335"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a> 
registered termination hooks. Threads not responding within 1 second are 
cancelled forcefully.
<li>Flush I/O and close all streams except for standard I/O.
<li>Reset the terminal if its properties were changed.
<li>Remove temporary files and incomplete compilation output.
<li>Reclaim memory.
</ul>

<p>
<li>Call exit(Status) to terminate the process
</ol>
</dd>
<dt class="pubdef"><a id="prolog/0"><strong>prolog</strong></a></dt>
<dd class="defbody">
This goal starts the default interactive top level. Queries are read 
from the stream <code>user_input</code>. See also the Prolog flag
<a class="flag" href="flags.html#flag:history">history</a>. The <a id="idx:prolog0:1336"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a> 
predicate is terminated (succeeds) by typing the end-of-file character 
(typically control-D).
</dd>
</dl>

<p>The following two hooks allow for expanding queries and handling the 
result of a query. These hooks are used by the top level variable 
expansion mechanism described in <a class="sec" href="topvars.html">section 
2.8</a>.

<dl class="latex">
<dt class="pubdef"><a id="expand_query/4"><strong>expand_query</strong>(<var>+Query, 
-Expanded, +Bindings, -ExpandedBindings</var>)</a></dt>
<dd class="defbody">
Hook in module <code>user</code>, normally not defined. <var>Query</var> 
and
<var>Bindings</var> represents the query read from the user and the 
names of the free variables as obtained using <a id="idx:readterm3:1337"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>. 
If this predicate succeeds, it should bind <var>Expanded</var> and <var>ExpandedBindings</var> 
to the query and bindings to be executed by the top level. This 
predicate is used by the top level (<a id="idx:prolog0:1338"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>). 
See also <a id="idx:expandanswer2:1339"></a><a class="pred" href="toplevel.html#expand_answer/2">expand_answer/2</a> 
and
<a id="idx:termexpansion2:1340"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>.</dd>
<dt class="pubdef"><a id="expand_answer/2"><strong>expand_answer</strong>(<var>+Bindings, 
-ExpandedBindings</var>)</a></dt>
<dd class="defbody">
Hook in module <code>user</code>, normally not defined. Expand the 
result of a successfully executed top-level query. <var>Bindings</var> 
is the query
<var>&lt;<var>Name</var>&gt;=&lt;<var>Value</var>&gt;</var> binding list 
from the query. <var>ExpandedBindings</var> must be unified with the 
bindings the top level should print.
</dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / toplevel.html
