From: Mark Thom <markjordanthom@gmail.com>
Date: Sat, 30 Nov 2019 21:22:59 +0000 (-0700)
Subject: add sumlist/2 to lists.pl
X-Git-Tag: v0.8.118~36^2~14
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=27b659c401f2b509ce1ef404087a4faabd4ca4d3;p=scryer-prolog.git

add sumlist/2 to lists.pl
---

diff --git a/src/prolog/lib/lists.pl b/src/prolog/lib/lists.pl
index 4fc5de96..ae207403 100644
--- 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).