foldl(:Goal,
+List, +V0, -V)<= 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.