X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FInst.lhs;h=c009ebe0831f496d8265086255f61803ece626c1;hp=1a8efe2ebf0c54a3a86500593166b520c0f710ab;hb=a187566d4ce21b657fd5268373d0e3743d29d886;hpb=c93a92a5950a6343d93774cb07530deb8dd4ac3d

diff --git a/compiler/typecheck/Inst.lhs b/compiler/typecheck/Inst.lhs
index 1a8efe2..c009ebe 100644
--- a/compiler/typecheck/Inst.lhs
+++ b/compiler/typecheck/Inst.lhs
@@ -45,7 +45,8 @@ module Inst (
         mkIdEqInstCo, mkSymEqInstCo, mkLeftTransEqInstCo,
         mkRightTransEqInstCo, mkAppEqInstCo,
         isValidWantedEqInst,
-	eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst, finalizeEqInst, 
+	eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst,
+        wantedToLocalEqInst, finalizeEqInst, 
 	eqInstType, updateEqInstCoercion,
 	eqInstCoercion,	eqInstTys
     ) where
@@ -1095,6 +1096,15 @@ mkWantedEqInst pred@(EqPred ty1 ty2)
        }
 mkWantedEqInst pred = pprPanic "mkWantedEqInst" (ppr pred)
 
+-- Turn a wanted equality into a local that propagates the uninstantiated
+-- coercion variable as witness.  We need this to propagate wanted irreds into
+-- attempts to solve implication constraints.
+--
+wantedToLocalEqInst :: Inst -> Inst
+wantedToLocalEqInst eq@(EqInst {tci_co = Left cotv})
+  = eq {tci_co = Right (mkTyVarTy cotv)}
+wantedToLocalEqInst eq = eq
+
 -- Turn a wanted into a local EqInst (needed during type inference for
 -- signatures) 
 --