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

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<TITLE>SWI-Prolog 5.11.18 Reference Manual: Section 4.35</TITLE><LINK REL=home HREF="index.html">
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<H2><A NAME="sec:4.35"><SPAN class="sec-nr">4.35</SPAN> <SPAN class="sec-title">User 
Top-level Manipulation</SPAN></A></H2>

<A NAME="sec:toplevel"></A>

<DL class="latex">
<DT class="pubdef"><A NAME="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 NAME="idx:prolog0:1153"></A><A class="pred" href="toplevel.html#prolog/0">prolog/0</A>).</DD>
<DT class="pubdef"><A NAME="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 options 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 NAME="idx:catch3:1154"></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 NAME="idx:once1:1155"></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 NAME="halt/0"><STRONG>halt</STRONG></A></DT>
<DD class="defbody">
Terminate Prolog execution. Open files are closed and if the command 
line option <STRONG>-tty</STRONG> is not active the terminal status (see 
Unix stty(1)) is restored. Hooks may be registered both in Prolog and in 
foreign code. Prolog hooks are registered using <A NAME="idx:athalt1:1156"></A><A class="pred" href="consulting.html#at_halt/1">at_halt/1</A>. <A NAME="idx:halt0:1157"></A><A class="pred" href="toplevel.html#halt/0">halt/0</A> 
is equivalent to <CODE>halt(0)</CODE>.<SUP class="fn">bug<SPAN class="fn-text">In 
the multi-threaded version, <A NAME="idx:halt0:1158"></A><A class="pred" href="toplevel.html#halt/0">halt/0</A> 
does not work when not called from the <EM>main</EM> thread. In the 
current system a <CODE>permission_error</CODE> exception is raised. 
Future versions may enable <A NAME="idx:halt0:1159"></A><A class="pred" href="toplevel.html#halt/0">halt/0</A> 
from any thread.</SPAN></SUP></DD>
<DT class="pubdef"><span class="pred-tag">[ISO]</span><A NAME="halt/1"><STRONG>halt</STRONG>(<VAR>+Status</VAR>)</A></DT>
<DD class="defbody">
Terminate Prolog execution with given status. Status is an integer. See 
also <A NAME="idx:halt0:1160"></A><A class="pred" href="toplevel.html#halt/0">halt/0</A>.</DD>
<DT class="pubdef"><A NAME="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 NAME="idx:prolog0:1161"></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 NAME="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 NAME="idx:readterm3:1162"></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 NAME="idx:prolog0:1163"></A><A class="pred" href="toplevel.html#prolog/0">prolog/0</A>). 
See also <A NAME="idx:expandanswer2:1164"></A><A class="pred" href="toplevel.html#expand_answer/2">expand_answer/2</A> 
and
<A NAME="idx:termexpansion2:1165"></A><A class="pred" href="consulting.html#term_expansion/2">term_expansion/2</A>.</DD>
<DT class="pubdef"><A NAME="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 5.10.4-3ubuntu1 / usr / lib / swi-prolog / doc / Manual / toplevel.html
