Type families: bug fixes

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

diff --git a/compiler/basicTypes/Var.lhs b/compiler/basicTypes/Var.lhs
index 0c30ab4..eec6c80 100644 (file)
--- a/compiler/basicTypes/Var.lhs
+++ b/compiler/basicTypes/Var.lhs
@@ -273,8 +273,7 @@ mkTyVar name kind = ASSERT( not (isCoercionKind kind ) )
 
 mkTcTyVar :: Name -> Kind -> TcTyVarDetails -> TyVar
 mkTcTyVar name kind details
-  = -- TOM: no longer valid assertion? 
-    -- ASSERT( not (isCoercionKind kind) )
+  = -- NB: 'kind' may be a coercion kind; cf, 'TcMType.newMetaCoVar'
     TcTyVar {  varName    = name,
                realUnique = getKeyFastInt (nameUnique name),
                varType  = kind,
@@ -289,7 +288,7 @@ mkTcTyVar name kind details
 %************************************************************************
 
 \begin{code}
-type CoVar = Var       -- ^ A coercion variable is simply a type 
+type CoVar = Var -- A coercion variable is simply a type 
                        -- variable of kind @ty1 :=: ty2@. Hence its
                        -- 'varType' is always @PredTy (EqPred t1 t2)@
 
@@ -391,8 +390,9 @@ isLocalIdVar (LocalId {}) = True
 isLocalIdVar _            = False
 
 isCoVar :: Var -> Bool
-isCoVar (v@(TyVar {})) = isCoercionVar v
-isCoVar _              = False
+isCoVar (v@(TyVar {}))             = isCoercionVar v
+isCoVar (TcTyVar {varType = kind}) = isCoercionKind kind  -- used during solving
+isCoVar _                          = False
 
 -- | 'isLocalVar' returns @True@ for type variables as well as local 'Id's
 -- These are the variables that we need to pay attention to when finding free