Re: determinism

[Gregory Bourassa]

Daniel,

Does your solution not return one solution to the caller before it ascertains whether or not the goal is really deterministic?

This program is a bit simplistic and it actually tries G three times; but it only returns a solution if G is really deterministic.

det(G) :- retractall( success ),  call(G),  backtrack_only_once,  !,  fail.

det(G) :- success, call(G).

backtrack_only_once :- success.

backtrack_only_once :- not( success ),  assertz( success ), !, fail.

Regards.

Gregory Bourassa

 



On Mon Feb 12 12:11 , Daniel Diaz sent:

> michel levy a écrit :
> > Could you help to write this program :
> > det(T,G) succeeds if and only if G succeeds once and only once and give
> > the T answer.
> > 1) I don't want the solution below by findall, because I want to try at
> > most two back tracks on G.
> > det(T,G) :- findall(T,G,L),length(L,1)
> > 
> > 2) I know already call_det but it's not the solution because G can have
> > choice points, but only one answer.
> > 
>
> You can do it using a global variable to count solutions. Stop when the
> second is reached.
>
>
> det(Goal) :-
> det1(Goal).
>
> det(_) :-
> g_read(det_count, 1).
>
>
> det1(Goal) :-
> g_assign(det_count, 0),
> call(Goal),
> g_inc(det_count, Count), % increment and return the counter
> Count = 2, % cut if 2nd solution is reached (else fail)
> !,
> fail.
>
> Hope this helps
>
>
>
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