Comments and tidy-up

[ghc-hetmet.git] / compiler / types / FunDeps.lhs

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 9347f5f..5ece047 100644 (file)
--- 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}
@@ -17,9 +17,10 @@ module FunDeps (
 
 import Name            ( Name, getSrcLoc )
 import Var             ( TyVar )
-import Class           ( Class, FunDep, classTvsFds )
-import Unify           ( tcUnifyTys, BindFlag(..) )
+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,
@@ -125,6 +126,7 @@ oclose preds fixed_tvs
 
 \begin{code}
 grow :: [PredType] -> TyVarSet -> TyVarSet
+-- See Note [Ambiguity] in TcSimplify
 grow preds fixed_tvs 
   | null preds = fixed_tvs
   | otherwise  = loop fixed_tvs
@@ -218,8 +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])
@@ -484,17 +491,4 @@ trimRoughMatchTcs clas_tvs (ltvs,_) mb_tcs
 \end{code}
 
 
-%************************************************************************
-%*                                                                     *
-\subsection{Miscellaneous}
-%*                                                                     *
-%************************************************************************
-
-\begin{code}
-pprFundeps :: Outputable a => [FunDep a] -> SDoc
-pprFundeps [] = empty
-pprFundeps fds = hsep (ptext SLIT("|") : punctuate comma (map ppr_fd fds))
-
-ppr_fd (us, vs) = hsep [interppSP us, ptext SLIT("->"), interppSP vs]
-\end{code}