Did you know ... Search Documentation:
Predicate foldl/6
 foldl(:Goal, +List, +V0, -V)
 foldl(:Goal, +List1, +List2, +V0, -V)
 foldl(:Goal, +List1, +List2, +List3, +V0, -V)
 foldl(:Goal, +List1, +List2, +List3, +List4, +V0, -V)
Fold an ensemble of m (0 <= 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.

Tags are associated to your profile if you are logged in
Tags: