Re: too simple trace

[Daniel Diaz]

Note that permutation/2 and select/3 are predefined predicates 
(built-in). They are compiled (native code) and thus you cannot trace 
them. Simply rename permuntation as perm (and select as sel). And, after 
loading under the top-level (with consult), you will be able to trace them.

Good luck


Gilles Dégottex wrote:
> Hi all
>
>         I think gprolog does a too much simple trace on this exemple:
>
> permutation([], []).
> permutation(List, [S|Perm]) :-
>         select(S, List, Rest),
>         permutation(Rest, Perm).
>
> select(Element, [Element|Tail], Tail).
> select(Element, [Head|Tail1], [Head|Tail2]) :-
>         select(Element, Tail1, Tail2).
>
> =>
> "
> Prolog interruption (h for help) ? t
> The debugger will first creep -- showing everything (trace)
> | ?- permutation([1, 2, 3], L).
>       1    1  Call: permutation([1,2,3],_23) ?
>       1    1  Exit: permutation([1,2,3],[1,2,3]) ?
>
> L = [1,2,3] ?
>
> yes
> {trace}
> | ?-
> "
>
> no call to select, and no different trace if I press "shift+;" for the other 
> solutions. maybe I missed an option
>
> I thought it was a nice exemple for studients, to show the backtraking engine, 
> since they saw these two lines :)
>
> Tanks for comments
> Gilles
>
>
>
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