Prolog binding arguments

Question

In sicstus prolog, there's a predicate:

maplist(:Pred, +List)

Pred is supposed to take just one argument - List element. How can I pass a 2-argument predicate, with first argument defined? In other languages it would be written as:

maplist(pred.bind(SomeValue), List)

Answer 1

maplist(P_1, Xs) will call call(P_1, X) for each element of Xs. The built-in predicate call/2 adds one further argument to P_1 and then calls this with call/1. To indicate that a further argument is needed, it is very helpful to use a name like P_1 meaning "one extra argument is needed".

So if you have already a predicate of arity 2, say, (=)/2, you will pass =(2) to maplist:

?- maplist(=(2), Xs).
   Xs = []
;  Xs = [2]
;  Xs = [2,2]
;  ... .

Since the definition in SICStus' library is unfortunately incorrect, rather use the following definition:

:- meta_predicate(maplist(1,?)).
:- meta_predicate(maplist_i(?,1)).

maplist(P_1, Xs) :-
   maplist_i(Xs, P_1).

maplist_i([], _P_1).
maplist_i([E|Es], P_1) :-
   call(P_1, E),
   maplist_i(Es, P_1).

See this answer for more.

Just a nice further example about lists of lists.

?- Xss = [[A],[B,C]], maplist(maplist(=(E)), Xss).
   Xss = [[E], [E, E]], A = B, B = C, C = E.