Fix Trac #3017: ensure that we quantify over enough type variables when equalities...

[ghc-hetmet.git] / compiler / basicTypes / VarSet.lhs

diff --git a/compiler/basicTypes/VarSet.lhs b/compiler/basicTypes/VarSet.lhs
index 67a3dbf..6f03aad 100644 (file)
--- a/compiler/basicTypes/VarSet.lhs
+++ b/compiler/basicTypes/VarSet.lhs
@@ -15,7 +15,7 @@ module VarSet (
        unionVarSet, unionVarSets,
        intersectVarSet, intersectsVarSet, disjointVarSet,
        isEmptyVarSet, delVarSet, delVarSetList, delVarSetByKey,
-       minusVarSet, foldVarSet, filterVarSet,
+       minusVarSet, foldVarSet, filterVarSet, fixVarSet,
        lookupVarSet, mapVarSet, sizeVarSet, seqVarSet,
        elemVarSetByKey
     ) where
@@ -63,6 +63,7 @@ extendVarSet_C  :: (Var->Var->Var) -> VarSet -> Var -> VarSet
 
 delVarSetByKey :: VarSet -> Unique -> VarSet
 elemVarSetByKey :: Unique -> VarSet -> Bool
+fixVarSet       :: (VarSet -> VarSet) -> VarSet -> VarSet
 
 emptyVarSet    = emptyUniqSet
 unitVarSet     = unitUniqSet
@@ -100,6 +101,12 @@ elemVarSetByKey    = elemUniqSet_Directly
 intersectsVarSet s1 s2 = not (s1 `disjointVarSet` s2)
 disjointVarSet   s1 s2 = isEmptyVarSet (s1 `intersectVarSet` s2)
 subVarSet        s1 s2 = isEmptyVarSet (s1 `minusVarSet` s2)
+
+-- Iterate f to a fixpoint
+fixVarSet f s | new_s `subVarSet` s = s
+             | otherwise           = fixVarSet f new_s 
+             where
+               new_s = f s
 \end{code}
 
 \begin{code}