import HsSyn
-import Type ( Type, isUnLiftedType, tyVarsOfType, tyVarsOfTypes,
+import Type ( Type, isUnLiftedType, tyVarsOfType,
isTyVarTy, getTyVar_maybe, funTyCon
)
import TcHsSyn ( mkSimpleHsAlt )
(local_tvs, _, tau) = tcSplitSigmaTy ty
valid ty
- | isTyVarTy ty = True
- | no_tyvars_in_ty = True
- | otherwise = case tcSplitTyConApp_maybe ty of
+ | not (isTauTy ty) = False -- Note [Higher ramk methods]
+ | isTyVarTy ty = True
+ | no_tyvars_in_ty = True
+ | otherwise = case tcSplitTyConApp_maybe ty of
Just (tc,tys) -> valid_tycon tc && all valid tys
Nothing -> False
where
instance Foo T where
op = \b. \dict::Ord b. toOp b (op Trep b dict)
+Note [Higher rank methods]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+Higher-rank method types don't work, because we'd generate a bimap that
+needs impredicative polymorphism. In principle that should be possible
+(with boxy types and all) but it would take a bit of working out. Here's
+an example:
+ class ChurchEncode k where
+ match :: k -> z
+ -> (forall a b z. a -> b -> z) {- product -}
+ -> (forall a z. a -> z) {- left -}
+ -> (forall a z. a -> z) {- right -}
+ -> z
+
+ match {| Unit |} Unit unit prod left right = unit
+ match {| a :*: b |} (x :*: y) unit prod left right = prod x y
+ match {| a :+: b |} (Inl l) unit prod left right = left l
+ match {| a :+: b |} (Inr r) unit prod left right = right r
+
\begin{code}
mkGenericRhs :: Id -> TyVar -> TyCon -> LHsExpr RdrName
mkGenericRhs sel_id tyvar tycon
-> EP (LHsExpr RdrName)
-- Top level case - splitting the TyCon.
generate_bimap env@(tv,ep,local_tvs) ty
- = case getTyVar_maybe ty of
- Just tv1 | tv == tv1 -> ep -- The class tyvar
- | otherwise -> ASSERT( tv1 `elem` local_tvs) -- One of the polymorphic tyvars of the method
- idEP
- Nothing -> bimapApp env (tcSplitTyConApp_maybe ty)
+ | all (`elem` local_tvs) (varSetElems (tyVarsOfType ty))
+ = idEP -- A constant type
+
+ | Just tv1 <- getTyVar_maybe ty
+ = ASSERT( tv == tv1 ) ep -- The class tyvar
+
+ | Just (tycon, ty_args) <- tcSplitTyConApp_maybe ty
+ = bimapTyCon tycon (map (generate_bimap env) ty_args)
+
+ | otherwise
+ = pprPanic "generate_bimap" (ppr ty)
-------------------
-bimapApp :: EPEnv -> Maybe (TyCon, [Type]) -> EP (LHsExpr RdrName)
-bimapApp env Nothing = panic "TcClassDecl: Type Application!"
-bimapApp env (Just (tycon, ty_args))
+bimapTyCon :: TyCon -> [EP (LHsExpr RdrName)] -> EP (LHsExpr RdrName)
+bimapTyCon tycon arg_eps
| tycon == funTyCon = bimapArrow arg_eps
| tycon == listTyCon = bimapList arg_eps
| isBoxedTupleTyCon tycon = bimapTuple arg_eps
- | otherwise = -- Otherwise validGenericMethodType will
- -- have checked that the type is a constant type
- ASSERT( all (`elem` local_tvs) (varSetElems (tyVarsOfTypes ty_args)) )
- idEP
- where
- arg_eps = map (generate_bimap env) ty_args
- (_,_,local_tvs) = env
+ | otherwise = pprPanic "bimapTyCon" (ppr tycon)
-------------------
-- bimapArrow :: [EP a a', EP b b'] -> EP (a->b) (a'->b')