[m-rev.] diff: add a function version of kv_list.foldl

[Julien Fischer]

Add a function version of kv_list.foldl.

library/kv_list.m:
     As above.

Julien.

diff --git a/library/kv_list.m b/library/kv_list.m
index 301237f..10b52ff 100644
--- a/library/kv_list.m
+++ b/library/kv_list.m
@@ -205,6 +205,13 @@
  % Folding over kv_lists.
  %

+    % foldl(Func, List, Start) = End calls Func
+    % with each key-value in List, working left-to-right,
+    % and an accumulator whose initial value is Start,
+    % and returns the final value in End.
+    %
+:- func foldl(func(K, V, A) = A, kv_list(K, V), A) = A.
+
      % foldl(Pred, List, Start End) calls Pred
      % with each key-value pair in List, working left-to-right,
      % and an accumulator whose initial value is Start,
@@ -558,6 +565,11 @@ merge(A @ kv_cons(AK, AV, AKVs), B @ kv_cons(BK, BV, BKVs), C) :-

  %---------------------------------------------------------------------------%

+foldl(_F, kv_nil, A) = A.
+foldl(F, kv_cons(K, V, TailKVs), !.A) = !:A :-
+    !:A = F(K, V, !.A),
+    !:A = foldl(F, TailKVs, !.A).
+
  foldl(_P, kv_nil, !A).
  foldl(P, kv_cons(K, V, TailKVs), !A) :-
      P(K, V, !A),