From: Markus Triska <triska@metalevel.at>
Date: Sat, 22 Aug 2020 15:49:02 +0000 (+0200)
Subject: dif/2: Omit entailed residual goals, if the arguments are not unifiable.
X-Git-Tag: v0.9.0~174^2~8^2
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=cc77ef680d270913a85e6b2d062ac1950233a9f2;p=scryer-prolog.git

dif/2: Omit entailed residual goals, if the arguments are not unifiable.

This addresses #135.
---

diff --git a/src/lib/dif.pl b/src/lib/dif.pl
index ad3053ec..bb92979a 100644
--- a/src/lib/dif.pl
+++ b/src/lib/dif.pl
@@ -49,7 +49,9 @@ dif(X, Y) :-
 
 gather_dif_goals([]) --> [].
 gather_dif_goals([(X \== Y) | Goals]) -->
-    [dif(X, Y)],
+    (   { X \= Y } -> []
+    ;   [dif(X, Y)]
+    ),
     gather_dif_goals(Goals).
 
 attribute_goals(X) -->