From: Markus Triska <triska@metalevel.at>
Date: Sat, 22 Apr 2023 22:37:03 +0000 (+0200)
Subject: ADDED: dif_si/2
X-Git-Tag: v0.9.2~147^2
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=8b7281fad08db58cc00e5c7cb5fdc43b4dc3f24f;p=scryer-prolog.git

ADDED: dif_si/2

Source: https://stackoverflow.com/questions/20223390/prolog-a-person-is-a-sibling-of-himself

In Scryer Prolog, this is actually not needed, since Scryer Prolog provides
dif/2 in library(dif). However, it is still useful to provide dif_si/2 for two reasons:

  1) to more easily port code from systems where only dif_si/2 is available
  2) to provide correct disequality in other systems that adopt this library
---

diff --git a/src/lib/si.pl b/src/lib/si.pl
index a1705343..4c3b6c65 100644
--- a/src/lib/si.pl
+++ b/src/lib/si.pl
@@ -36,7 +36,8 @@
                integer_si/1,
                atomic_si/1,
                list_si/1,
-               chars_si/1]).
+               chars_si/1,
+               dif_si/2]).
 
 :- use_module(library(lists)).
 
@@ -64,3 +65,9 @@ list_si(L0) :-
 chars_si(Cs) :-
    list_si(Cs),
    '$is_partial_string'(Cs).
+
+dif_si(X, Y) :-
+   X \== Y,
+   ( X \= Y -> true
+   ; throw(error(instantiation_error,dif_si/2))
+   ).