:- use_module(library(apply)).(can be autoloaded)
<=4) lists of length n head-to-tail ("scan-left"), using columns of m list elements as arguments for Goal. The
scanlfamily 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