Added emulation of the =@=/2 predicate to the SWI-Prolog compatibility library.

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1891 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

docs/swi.tex

@@ -107,6 +107,13 @@ and change working directory to @var{New}.  Use the pattern
 @code{working_directory(CWD, CWD)} to get the current directory.  See
 also @code{absolute_file_name/2} and @code{chdir/1}.
 
+@item @@@var{Term1} =@@= @@@var{Term2}
+@findex =@@=/2
+@snindex =@@=/2
+@cnindex =@@=/2
+
+True iff @var{Term1} and @var{Term2} are structurally equivalent. I.e. if @var{Term1} and @var{Term2} are variants of each other.
+
 @end table
 
 @node Invoking Predicates on all Members of a List,Forall, , SWI-Prolog

library/swi.yap

@@ -20,7 +20,8 @@
 
 :- use_module(library(terms),[term_variables/2,
 			      term_variables/3,
-			      term_hash/2]).
+			      term_hash/2,
+			      variant/2]).
 
 :- multifile
    prolog:message/3.
@@ -238,3 +239,7 @@ prolog:intersection([_|T], L, R) :-
 	prolog:intersection(T, L, R).
 
 
+:- op(700, xfx, '=@=').
+
+prolog:(Term1 =@= Term2) :-
+	variant(Term1, Term2), !.