X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FInst.lhs;h=13b8be80b8fdcd3f3bb9ea3de8237bba4bd7d0b2;hp=8d21d1bcb190b8973b99d40035e75f5c8e8a7b94;hb=4ba96c06f2b69ea1fe2b27718013713e94c1520c;hpb=7fc749a43b4b6b85d234fa95d4928648259584f4

diff --git a/compiler/typecheck/Inst.lhs b/compiler/typecheck/Inst.lhs
index 8d21d1b..13b8be8 100644
--- a/compiler/typecheck/Inst.lhs
+++ b/compiler/typecheck/Inst.lhs
@@ -48,7 +48,7 @@ module Inst (
 
 	mkWantedCo, mkGivenCo,
 	fromWantedCo, fromGivenCo,
-	eitherEqInst, mkEqInst, mkEqInsts,
+	eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst,
 	finalizeEqInst, writeWantedCoercion,
 	eqInstType, updateEqInstCoercion,
 	eqInstCoercion,
@@ -979,11 +979,10 @@ fromWantedCo :: String -> Either TcTyVar Coercion -> TcTyVar
 fromWantedCo _ (Left covar) = covar
 fromWantedCo msg _	    = panic ("fromWantedCo: not a wanted coercion: " ++ msg)
 
-eitherEqInst 
-	:: Inst 		-- given or wanted EqInst
-	-> (TcTyVar  -> a) 	-- 	result if wanted
-	-> (Coercion -> a) 	--	result if given
-	-> a		
+eitherEqInst :: Inst 	            -- given or wanted EqInst
+	     -> (TcTyVar  -> a)     -- 	result if wanted
+	     -> (Coercion -> a)     --	result if given
+	     -> a		
 eitherEqInst (EqInst {tci_co = either_co}) withWanted withGiven
 	= case either_co of
 		Left  covar -> withWanted covar
@@ -1004,6 +1003,12 @@ mkEqInst (EqPred ty1 ty2) co
 	     }
 	where mkName uniq src_span = mkInternalName uniq (mkVarOcc "co") src_span
 
+mkWantedEqInst :: PredType -> TcM Inst
+mkWantedEqInst pred@(EqPred ty1 ty2)
+  = do { cotv <- newMetaTyVar TauTv (mkCoKind ty1 ty2)
+       ; mkEqInst pred (Left cotv)
+       }
+
 -- type inference:
 --	We want to promote the wanted EqInst to a given EqInst
 --	in the signature context.