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<H1><A NAME="SEC430" HREF="ciao_toc.html#TOC430">Call on determinate</A></H1>
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<A NAME="IDX5381"></A>
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<STRONG>Author(s):</STRONG> José Morales, Manuel Carro.
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<STRONG>Version:</STRONG> 1.7#149 (2001/11/19, 19:17:51 CET)
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Offers an enriched variant of call and cut <CODE>!!/0</CODE> which executes pending goals when the computation has no more alternatives.
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This library is useful to, for example, get rid of external connections once the necessary data has been obtained.
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<LI><A HREF="ciao_104.html#SEC431">Usage and interface (det_hook_rt)</A>
<LI><A HREF="ciao_104.html#SEC432">Documentation on exports (det_hook_rt)</A>
<LI><A HREF="ciao_104.html#SEC433">Documentation on internals (det_hook_rt)</A>
<LI><A HREF="ciao_104.html#SEC434">Other information (det_hook_rt)</A>
<LI><A HREF="ciao_104.html#SEC435">Known bugs and planned improvements (det_hook_rt)</A>
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<H2><A NAME="SEC431" HREF="ciao_toc.html#TOC431">Usage and interface (<CODE>det_hook_rt</CODE>)</A></H2>
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<LI><STRONG>Library usage:</STRONG>
<PRE>
:- use_module(library(det_hook_rt)).
</PRE>
in which case, <CODE>!!/0</CODE> is not available.
Typically, this library is used as a package:
<PRE>
:- use_package(det_hook).
</PRE>
<LI><STRONG>Exports:</STRONG>
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<LI><EM>Predicates:</EM>
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<CODE>det_try/3</CODE>.
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<H2><A NAME="SEC432" HREF="ciao_toc.html#TOC432">Documentation on exports (<CODE>det_hook_rt</CODE>)</A></H2>
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<DT><span class="define">PREDICATE:</span> <B>det_try/3:</B>
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<EM>Meta-predicate</EM> with arguments: <CODE>det_try(goal,goal,goal)</CODE>.
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<STRONG>Usage:</STRONG> <CODE>det_try(Goal, OnCut, OnFail)</CODE>
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<LI><EM>Description:</EM> <CODE>Action</CODE> is called, and <CODE>OnCut</CODE> and <CODE>OnFail</CODE> are goals to be executed when <CODE>Goal</CODE> is cut or when it finitely fails, respectively. In order for this to work, cutting must be performed in a special way, by using the
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<CODE>!!/0</CODE> predicate, also provided by this module.
<LI><EM>The following properties should hold at call time:</EM>
<CODE>Goal</CODE> is a term which represents a goal, i.e., an atom or a structure.
(<CODE>basic_props:callable/1</CODE>)
<CODE>OnCut</CODE> is a term which represents a goal, i.e., an atom or a structure.
(<CODE>basic_props:callable/1</CODE>)
<CODE>OnFail</CODE> is a term which represents a goal, i.e., an atom or a structure.
(<CODE>basic_props:callable/1</CODE>)
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</DL>
<H2><A NAME="SEC433" HREF="ciao_toc.html#TOC433">Documentation on internals (<CODE>det_hook_rt</CODE>)</A></H2>
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<DL>
<DT><span class="define">PREDICATE:</span> <B>!!/0:</B>
<DD><A NAME="IDX5389"></A>
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<STRONG>Usage:</STRONG>
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<LI><EM>Description:</EM> Performs a special cut which prunes alternatives away, as the usual cut, but which also executes the goals specified as <CODE>OnCut</CODE> for any call in the scope of the cut.
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<H2><A NAME="SEC434" HREF="ciao_toc.html#TOC434">Other information (<CODE>det_hook_rt</CODE>)</A></H2>
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As an example, the program
<PRE>
:- module(_, _, [det_hook]).
enumerate(X):-
display(enumerating), nl,
OnCut = (display('goal cut'), nl),
OnFail = (display('goal failed'), nl),
det_try(enum(X), OnCut, OnFail).
enum(1).
enum(2).
enum(3).
</PRE>
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behaves as follows:
<PRE>
?- enumerate(X).
enumerating
X = 1 ? ;
X = 2 ? ;
X = 3 ? ;
goal failed
</PRE>
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(note the message inserted on failure). The execution can be cut as follows:
<PRE>
?- use_package(det_hook).
{Including /home/clip/lib/ciao/ciao-1.7/library/det_hook/det_hook.pl
}
yes
?- enumerate(X), '!!'.
enumerating
goal cut
X = 1 ? ;
no
</PRE>
<H2><A NAME="SEC435" HREF="ciao_toc.html#TOC435">Known bugs and planned improvements (<CODE>det_hook_rt</CODE>)</A></H2>
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If the started goals do not exhaust their solutions, and '!!'/0 is not used, the database will populate with facts which will be consulted the next time a '!!'/0 is used. This could cause incorrect executions.
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