add sumlist/2 to lists.pl

diff --git a/src/prolog/lib/lists.pl b/src/prolog/lib/lists.pl
index 4fc5de96c6ba9b9522e22445272c49e7630f1906..ae20740363f3f115d38b75fd617360501f48b55e 100644 (file)
--- a/src/prolog/lib/lists.pl
+++ b/src/prolog/lib/lists.pl
@@ -1,7 +1,10 @@
 :- module(lists, [member/2, select/3, append/3, memberchk/2,
                  reverse/2, length/2, maplist/2, maplist/3,
                  maplist/4, maplist/5, maplist/6, maplist/7,
-                 maplist/8, maplist/9]).
+                 maplist/8, maplist/9, sumlist/2]).
+
+
+:- use_module(library(error)).
 
 
 length(Xs, N) :-
@@ -96,3 +99,13 @@ maplist(_, [], [], [], [], [], [], [], []).
 maplist(Cont, [E1|E1s], [E2|E2s], [E3|E3s], [E4|E4s], [E5|E5s], [E6|E6s], [E7|E7s], [E8|E8s]) :-
     call(Cont, E1, E2, E3, E4, E5, E6, E7),
     maplist(Cont, E1s, E2s, E3s, E4s, E5s, E6s, E7s, E8s).
+
+
+sumlist_([], S, S).
+sumlist_([N|Ns], S, S0) :-
+    S1 is S0 + N,
+    sumlist(Ns, S, S1).
+
+sumlist(Ns, S) :-
+    must_be(list, Ns),
+    sumlist_(Ns, S, 0).