X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcGadt.lhs;h=987a4c66e785ebaf8fb9d776019419bc4c6fcb9d;hp=4c1f70ecf153e8a44a09bcc4d17c9657527b3f35;hb=f4510d27c5883fe7e8570f4dd49d45a8b0122f2c;hpb=d29f86b1fe7daf919e9b47a9003daed74b812790

diff --git a/compiler/typecheck/TcGadt.lhs b/compiler/typecheck/TcGadt.lhs
index 4c1f70e..987a4c6 100644
--- a/compiler/typecheck/TcGadt.lhs
+++ b/compiler/typecheck/TcGadt.lhs
@@ -11,8 +11,9 @@
 
 \begin{code}
 module TcGadt (
-	Refinement, emptyRefinement, gadtRefine, 
-	refineType, refineResType,
+	Refinement, emptyRefinement, isEmptyRefinement, 
+	gadtRefine, 
+	refineType, refinePred, refineResType,
 	dataConCanMatch,
 	tcUnifyTys, BindFlag(..)
   ) where
@@ -22,6 +23,7 @@ module TcGadt (
 import HsSyn
 import Coercion
 import Type
+
 import TypeRep
 import DataCon
 import Var
@@ -61,6 +63,8 @@ instance Outputable Refinement where
 emptyRefinement :: Refinement
 emptyRefinement = (Reft emptyInScopeSet emptyVarEnv)
 
+isEmptyRefinement :: Refinement -> Bool
+isEmptyRefinement (Reft _ env) = isEmptyVarEnv env
 
 refineType :: Refinement -> Type -> Maybe (Coercion, Type)
 -- Apply the refinement to the type.
@@ -77,6 +81,17 @@ refineType (Reft in_scope env) ty
     tv_subst = mkTvSubst in_scope (mapVarEnv snd env)
     co_subst = mkTvSubst in_scope (mapVarEnv fst env)
  
+refinePred :: Refinement -> PredType -> Maybe (Coercion, PredType)
+refinePred (Reft in_scope env) pred
+  | not (isEmptyVarEnv env),		-- Common case
+    any (`elemVarEnv` env) (varSetElems (tyVarsOfPred pred))
+  = Just (mkPredTy (substPred co_subst pred), substPred tv_subst pred)
+  | otherwise
+  = Nothing	-- The type doesn't mention any refined type variables
+  where
+    tv_subst = mkTvSubst in_scope (mapVarEnv snd env)
+    co_subst = mkTvSubst in_scope (mapVarEnv fst env)
+ 
 refineResType :: Refinement -> Type -> (HsWrapper, Type)
 -- Like refineType, but returns the 'sym' coercion
 -- If (refineResType r ty) = (co, ty')