X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=5ece0471884ec94b704736a60133a1328c7ce17f;hb=a7bda9e63ce091e4f33b6058a96686d7cde3d40d;hp=1534dc66f18da9be3eb2aa4cee65cd6a43e97aab;hpb=c76c69c5b62f1ca4fa52d75b0dfbd37b7eddbb09;p=ghc-hetmet.git

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 1534dc6..5ece047 100644
--- a/compiler/types/FunDeps.lhs
+++ b/compiler/types/FunDeps.lhs
@@ -1,4 +1,4 @@
-%
+
 % (c) The GRASP/AQUA Project, Glasgow University, 2000
 %
 \section[FunDeps]{FunDeps - functional dependencies}
@@ -20,6 +20,7 @@ import Var		( TyVar )
 import Class		( Class, FunDep, pprFundeps, classTvsFds )
 import TcGadt		( tcUnifyTys, BindFlag(..) )
 import Type		( substTys, notElemTvSubst )
+import Coercion         ( isEqPred )
 import TcType		( Type, PredType(..), tcEqType, 
 			  predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred )
 import InstEnv		( Instance(..), InstEnv, instanceHead, classInstances,
@@ -219,8 +220,13 @@ NOTA BENE:
 
 \begin{code}
 improve inst_env preds
-  = [ eqn | group <- equivClassesByUniq (predTyUnique . fst) preds,
+  = [ eqn | group <- equivClassesByUniq (predTyUnique . fst) (filterEqPreds preds),
 	    eqn   <- checkGroup inst_env group ]
+  where 
+    filterEqPreds = filter (not . isEqPred . fst)
+	-- Equality predicates don't have uniques
+	-- In any case, improvement *generates*, rather than
+	-- *consumes*, equality constraints
 
 ----------
 checkGroup :: (Class -> [Instance])