It seems foldl/6 is missing from lists.pl (as per Prologue to Prolog)

[infradig]

Only foldl/4-5 is provided and foldl/6 is depleted. Forgive the trivialness... on a par with the maplist/9 surfeit.

[UWN]

... trivialness...

meaning belonging to the trivium

[infradig]

And while i'm at it... why sum_list/2 and not list_sum/2 to use the modern form of such things. I know sum_list/2 is SWI compatible.

[UWN]

And then there is sumlist/2. And implementations vary as to ?- sumlist(Xs, N).