mkForAllCoercion, mkFunCoercion, mkInstsCoercion, mkUnsafeCoercion,
mkNewTypeCoercion, mkFamInstCoercion, mkAppsCoercion,
- splitNewTypeRepCo_maybe, decomposeCo,
+ splitNewTypeRepCo_maybe, instNewTyCon_maybe, decomposeCo,
unsafeCoercionTyCon, symCoercionTyCon,
transCoercionTyCon, leftCoercionTyCon,
+instNewTyCon_maybe :: TyCon -> [Type] -> Maybe (Type, CoercionI)
+-- instNewTyCon_maybe T ts
+-- = Just (rep_ty, co) if co : T ts ~ rep_ty
+instNewTyCon_maybe tc tys
+ | Just (tvs, ty, mb_co_tc) <- unwrapNewTyCon_maybe tc
+ = ASSERT( tys `lengthIs` tyConArity tc )
+ Just (substTyWith tvs tys ty,
+ case mb_co_tc of
+ Nothing -> IdCo
+ Just co_tc -> ACo (mkTyConApp co_tc tys))
+ | otherwise
+ = Nothing
+
-- this is here to avoid module loops
splitNewTypeRepCo_maybe :: Type -> Maybe (Type, Coercion)
-- Sometimes we want to look through a newtype and get its associated coercion
-- It only strips *one layer* off, so the caller will usually call itself recursively
-- Only applied to types of kind *, hence the newtype is always saturated
+-- splitNewTypeRepCo_maybe ty
+-- = Just (ty', co) if co : ty ~ ty'
+-- Returns Nothing for non-newtypes or fully-transparent newtypes
splitNewTypeRepCo_maybe ty
| Just ty' <- coreView ty = splitNewTypeRepCo_maybe ty'
splitNewTypeRepCo_maybe (TyConApp tc tys)
- | isClosedNewTyCon tc
- = ASSERT( tys `lengthIs` tyConArity tc ) -- splitNewTypeRepCo_maybe only be applied
- -- to *types* (of kind *)
- case newTyConRhs tc of
- (tvs, rep_ty) ->
- ASSERT( length tvs == length tys )
- Just (substTyWith tvs tys rep_ty, mkTyConApp co_con tys)
- where
- co_con = maybe (pprPanic "splitNewTypeRepCo_maybe" (ppr tc)) id (newTyConCo_maybe tc)
-splitNewTypeRepCo_maybe other = Nothing
+ | Just (ty', coi) <- instNewTyCon_maybe tc tys
+ = case coi of
+ ACo co -> Just (ty', co)
+ IdCo -> panic "splitNewTypeRepCo_maybe"
+ -- This case handled by coreView
+splitNewTypeRepCo_maybe other
+ = Nothing
\end{code}
\begin{code}
-
-- CoercionI is either
-- (a) proper coercion
-- (b) the identity coercion
-data CoercionI = IdCo | ACo Coercion
+data CoercionI = IdCo | ACo Coercion
isIdentityCoercion :: CoercionI -> Bool
isIdentityCoercion IdCo = True