]
checkRepTyCon :: (TyCon -> Bool) -> Type -> Bool
- -- Look through newtypes
- -- Non-recursive ones are transparent to splitTyConApp,
- -- but recursive ones aren't. Manuel had:
- -- newtype T = MkT (Ptr T)
- -- and wanted it to work...
-checkRepTyCon check_tc ty
- | Just (ty', _) <- splitNewTypeRepCo_maybe ty = checkRepTyCon check_tc ty'
- | Just (tc,_) <- splitTyConApp_maybe ty = check_tc tc
- | otherwise = False
+-- Look through newtypes, but *not* foralls
+-- Should work even for recursive newtypes
+-- eg Manuel had: newtype T = MkT (Ptr T)
+checkRepTyCon check_tc ty
+ = go [] ty
+ where
+ go rec_nts ty
+ | Just (tc,tys) <- splitTyConApp_maybe ty
+ = case carefullySplitNewType_maybe rec_nts tc tys of
+ Just (rec_nts', ty') -> go rec_nts' ty'
+ Nothing -> check_tc tc
+ | otherwise
+ = False
checkRepTyConKey :: [Unique] -> Type -> Bool
-- Like checkRepTyCon, but just looks at the TyCon key
applyTy, applyTys, applyTysD, isForAllTy, dropForAlls,
-- (Newtypes)
- newTyConInstRhs,
+ newTyConInstRhs, carefullySplitNewType_maybe,
-- (Type families)
tyFamInsts, predFamInsts,
-- | Looks through:
--
-- 1. For-alls
---
-- 2. Synonyms
---
-- 3. Predicates
---
--- 4. Usage annotations
---
--- 5. All newtypes, including recursive ones, but not newtype families
+-- 4. All newtypes, including recursive ones, but not newtype families
--
-- It's useful in the back end of the compiler.
repType :: Type -> Type
go rec_nts (ForAllTy _ ty) -- Look through foralls
= go rec_nts ty
- go rec_nts ty@(TyConApp tc tys) -- Expand newtypes
- | Just _co_con <- newTyConCo_maybe tc -- See Note [Expanding newtypes]
- = if tc `elem` rec_nts -- in Type.lhs
- then ty
- else go rec_nts' nt_rhs
- where
- nt_rhs = newTyConInstRhs tc tys
- rec_nts' | isRecursiveTyCon tc = tc:rec_nts
- | otherwise = rec_nts
+ go rec_nts (TyConApp tc tys) -- Expand newtypes
+ | Just (rec_nts', ty') <- carefullySplitNewType_maybe rec_nts tc tys
+ = go rec_nts' ty'
go _ ty = ty
+carefullySplitNewType_maybe :: [TyCon] -> TyCon -> [Type] -> Maybe ([TyCon],Type)
+-- Return the representation of a newtype, unless
+-- we've seen it already: see Note [Expanding newtypes]
+carefullySplitNewType_maybe rec_nts tc tys
+ | isNewTyCon tc
+ , not (tc `elem` rec_nts) = Just (rec_nts', newTyConInstRhs tc tys)
+ | otherwise = Nothing
+ where
+ rec_nts' | isRecursiveTyCon tc = tc:rec_nts
+ | otherwise = rec_nts
+
+
-- ToDo: this could be moved to the code generator, using splitTyConApp instead
-- of inspecting the type directly.