update length to use skip_list/3.

2012-01-09 23:46:17 +00:00 · 2012-01-09 23:46:17 +00:00 · 805ad7f958
commit 805ad7f958
parent 3f97a3f24a
1 changed files with 6 additions and 1 deletions
--- a/pl/sort.yap
+++ b/pl/sort.yap
@ -24,7 +24,12 @@

 %   length of a list.

-length(L,M) :- ( var(M) -> '$$_length1'(L,M,0) ; '$$_length2'(L, M) ).
+length(L, M) :-
+	  '$skip_list'(M0, L, R),
+	  ( R == [] -> M = M0 ;
+	    var(R) -> '$$_length1'(R, M, M0) ;
+	    '$do_error'(type_error(list,L),length(L,M))
+	  ).

 '$$_length1'([], M, M).
 '$$_length1'([_|L], O, N) :-