Remember to zonk FlatSkols!

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index 492cbf9..d5c794b 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -946,14 +946,14 @@ zonkType unbound_var_fn ty
 zonk_tc_tyvar :: (TcTyVar -> TcM Type) -- What to do for an unbound mutable var
              -> TcTyVar -> TcM TcType
 zonk_tc_tyvar unbound_var_fn tyvar 
-  | not (isMetaTyVar tyvar)    -- Skolems
-  = return (TyVarTy tyvar)
-
-  | otherwise                  -- Mutables
-  = do { cts <- readMetaTyVar tyvar
-       ; case cts of
-           Flexi       -> unbound_var_fn tyvar    -- Unbound meta type variable
-           Indirect ty -> zonkType unbound_var_fn ty  }
+  = ASSERT( isTcTyVar tyvar )
+    case tcTyVarDetails tyvar of
+      SkolemTv {}  -> return (TyVarTy tyvar)
+      FlatSkol ty  -> zonkType unbound_var_fn ty
+      MetaTv _ ref -> do { cts <- readMutVar ref
+                        ; case cts of    
+                            Flexi       -> unbound_var_fn tyvar  
+                            Indirect ty -> zonkType unbound_var_fn ty  }
 
 -- Zonk the kind of a non-TC tyvar in case it is a coercion variable (their
 -- kind contains types).