Fix bug in match

extra/match/match-tests.factor

@@ -5,6 +5,8 @@ IN: temporary
 
 MATCH-VARS: ?a ?b ;
 
+[ f ] [ { ?a ?a } { 1 2 } match ] unit-test
+
 [ H{ { ?a 1 } { ?b 2 } } ] [
  { ?a ?b } { 1 2 } match
 ] unit-test

extra/match/match.factor

@@ -3,7 +3,7 @@
 !
 ! Based on pattern matching code from Paul Graham's book 'On Lisp'.
 USING: parser kernel words namespaces sequences tuples
-combinators macros ;
+combinators macros assocs ;
 IN: match
 
 SYMBOL: _
@@ -22,10 +22,13 @@ SYMBOL: _
 : match-var? ( symbol -- bool )
     dup word? [ "match-var" word-prop ] [ drop f ] if ;
 
+: set-match-var ( value var -- ? )
+    dup namespace key? [ get = ] [ set t ] if ;
+
 : (match) ( value1 value2 -- matched? )
     {
-        { [ dup match-var? ] [ set t ] }
-        { [ over match-var? ] [ swap set t ] }
+        { [ dup match-var? ] [ set-match-var ] }
+        { [ over match-var? ] [ swap set-match-var ] }
         { [ 2dup = ] [ 2drop t ] }
         { [ 2dup [ _ eq? ] either? ] [ 2drop t ] }
         { [ 2dup [ sequence? ] both? ] [