tighten reverse/2

2019-03-03 10:37:34 -07:00
parent 74521a93d3
commit 3fc0a230fa
1 changed files with 4 additions and 1 deletions
--- a/src/prolog/lib/lists.pl
+++ b/src/prolog/lib/lists.pl
@@ -41,7 +41,10 @@ append([X|L], R, [X|S]) :- append(L, R, S).

 memberchk(X, Xs) :- member(X, Xs), !.

-reverse(Xs, Ys) :- reverse(Xs, Ys, [], [], Xs).
+reverse(Xs, Ys) :-
+    (  var(Ys) -> reverse(Xs, Ys, [], [], Xs)
+    ;  reverse(Ys, Xs, [], [], Ys)
+    ).

 reverse([], [], XsRev, YsRev, YsRev).
 reverse([X1|Xs], [Y1|Ys], XsPreludeRev, YsPreludeRev, Xss) :-