This module defines meta-predicates that apply a predicate on all members of a list.
All predicates support partial application in the Goal argument. This means that these calls are identical:
?- maplist(=, [foo, foo], [X, Y]). ?- maplist(=(foo), [X, Y]).
call(Goal, Xi) 
succeeds.
call(Goal, Xi) 
fails.
call(Pred, X) succeeds and
Excluded contains the remaining elements.
call(Pred, Xi, Place), 
where Place must be unified to one of <, = 
or >.
Pred must be deterministic.
maplist(G, [X_11, ..., X_1n],
           [X_21, ..., X_2n],
           ...,
           [X_m1, ..., X_mn]) :-
   call(G, X_11, ..., X_m1),
   call(G, X_12, ..., X_m2),
   ...
   call(G, X_1n, ..., X_mn).
This family of predicates is deterministic iff Goal is 
deterministic and List1 is a proper list, i.e., a list that 
ends in [].
call(Goal, ElemIn, _) fails are 
omitted from ListOut. For example (using library(yall)):
?- convlist([X,Y]>>(integer(X), Y is X^2),
            [3, 5, foo, 2], L).
L = [9, 25, 4].
<= m <= 
4) lists of length n head-to-tail ("fold-left"), using columns of m 
list elements as arguments for Goal. The foldl 
family of predicates is defined as follows, with V0 an 
initial value and V the final value of the folding operation:
foldl(G, [X_11, ..., X_1n],
         [X_21, ..., X_2n],
         ...,
         [X_m1, ..., X_mn], V0, V) :-
   call(G, X_11, ..., X_m1, V0, V1),
   call(G, X_12, ..., X_m2, V1, V2),
   ...
   call(G, X_1n, ..., X_mn, V<n-1>, V).
No implementation for a corresponding foldr is given. A foldr 
implementation would consist in first calling reverse/2 
on each of the m input lists, then applying the appropriate foldl. 
This is actually more efficient than using a properly programmed-out 
recursive algorithm that cannot be tail-call optimized.
<= m <= 
4) lists of length n head-to-tail ("scan-left"), using columns of m 
list elements as arguments for Goal. The scanl 
family of predicates is defined as follows, with V0 an 
initial value and V the final value of the scanning 
operation:
scanl(G, [X_11, ..., X_1n],
         [X_21, ..., X_2n],
         ...,
         [X_m1, ..., X_mn], V0, [V0, V1, ..., Vn] ) :-
   call(G, X_11, ..., X_m1, V0, V1),
   call(G, X_12, ..., X_m2, V1, V2),
   ...
   call(G, X_1n, ..., X_mn, V<n-1>, Vn).
scanl behaves like a foldl that collects 
the sequence of values taken on by the Vx accumulator into a 
list.