-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details
module Inst (
mkWantedCo, mkGivenCo,
fromWantedCo, fromGivenCo,
- eitherEqInst, mkEqInst, mkEqInsts,
+ eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst,
finalizeEqInst, writeWantedCoercion,
eqInstType, updateEqInstCoercion,
eqInstCoercion,
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
}
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.