[mercury-users] (Newbie) translating this from Prolog?

[Maurizio Colucci]

On Saturday 20 March 2004 19:09, Fergus Henderson wrote:
> Do the predicates in the list have side effects?
> If not, this can be translated as
>
>         :- pred holds(list(pred)).
>         :- mode holds(in(list_skel(pred is semidet))) is semidet.
>
>         holds(List) :-
>                 all [M] (member(M, List) => call(M)).
>
> If they have side effects, but can't fail, then it could be translated to
>
>         :- pred holds(list(pred(io__state, io__state), io__state,
> io__state). :- mode holds(in(list_skel(pred(di,uo) is det))) is det.
>
>         holds([]) --> [].
>         holds([M|Ms]) --> call(M), holds(Ms).
>
> If the predicates in the list have side effects but can fail,
> then you'd probably need to rewrite them so that they return a
> value of type bool or maybe(T) rather than failing.

Thank you, this code is very instructive.  I am going to study it.

(PS: I couldn't find "all" in the reference manual, maybe it's my fault)

Mau


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