From d5b6bcb035bf5150965129adee741740b7490883 Mon Sep 17 00:00:00 2001
From: Jan Wielemaker <jan@swi-prolog.org>
Date: Mon, 2 Dec 2024 11:04:10 +0100
Subject: [PATCH] ENHANCED: gui tracer support for `Head ==> Body` rules.

---
 library/prolog_clause.pl | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/library/prolog_clause.pl b/library/prolog_clause.pl
index 691f1cf2ee..6dfc57e54a 100644
--- a/library/prolog_clause.pl
+++ b/library/prolog_clause.pl
@@ -3,7 +3,7 @@
     Author:        Jan Wielemaker
     E-mail:        J.Wielemaker@vu.nl
     WWW:           http://www.swi-prolog.org
-    Copyright (c)  2005-2023, University of Amsterdam
+    Copyright (c)  2005-2024, University of Amsterdam
                               VU University Amsterdam
                               CWI, Amsterdam
                               SWI-Prolog Solutions b.v.
@@ -280,8 +280,10 @@
     functor(Bindings, varnames, L),
     do_make_varnames(Offsets, Names, Bindings).
 
-dcg_head((Head --> _Body), Head).
-dcg_head((Head ==> _Body), Head).
+dcg_head((Head,_ --> _Body), Head).
+dcg_head((Head   --> _Body), Head).
+dcg_head((Head,_ ==> _Body), Head).
+dcg_head((Head   ==> _Body), Head).
 
 do_make_varnames([], _, _).
 do_make_varnames([N=Var|TO], Names, Bindings) :-
@@ -405,6 +407,12 @@
 unify_clause((Head => Body), Compiled1, Module, TermPos0, TermPos) :-
     !,
     unify_clause2((Head :- Body), Compiled1, Module, TermPos0, TermPos).
+unify_clause(Read, Compiled1, Module, TermPos0, TermPos) :-
+    Read = (_ ==> _),
+    ci_expand(Read, Compiled2, Module, TermPos0, TermPos1),
+    Compiled2 \= (_ ==> _),
+    !,
+    unify_clause(Compiled2, Compiled1, Module, TermPos1, TermPos).
 unify_clause(Read, Decompiled, Module, TermPos0, TermPos) :-
     unify_clause2(Read, Decompiled, Module, TermPos0, TermPos).