import TypeRep
import Type ( Type, Kind, PredType, substTyWith, mkAppTy, mkForAllTy,
mkFunTy, splitAppTy_maybe, splitForAllTy_maybe, coreView,
- kindView, mkTyConApp, isCoercionKind, isEqPred, mkAppTys
+ kindView, mkTyConApp, isCoercionKind, isEqPred, mkAppTys,
+ coreEqType, splitAppTys, isTyVarTy, splitTyConApp_maybe
)
import TyCon ( TyCon, tyConArity, mkCoercionTyCon, isNewTyCon,
newTyConRhs, newTyConCo,
------------------------------
decomposeCo :: Arity -> Coercion -> [Coercion]
-- (decomposeCo 3 c) = [right (left (left c)), right (left c), right c]
+-- So this breaks a coercion with kind T A B C :=: T D E F into
+-- a list of coercions of kinds A :=: D, B :=: E and E :=: F
decomposeCo n co
= go n co []
where
coercionKind :: Coercion -> (Type, Type)
-- c :: (t1 :=: t2)
-- Then (coercionKind c) = (t1,t2)
-
coercionKind (TyVarTy a) | isCoVar a = splitCoercionKind (tyVarKind a)
| otherwise = let t = (TyVarTy a) in (t, t)
coercionKind (AppTy ty1 ty2)
(mkAppTy t1 s1, mkAppTy t2 s2)
coercionKind (TyConApp tc args)
| Just (ar, rule) <- isCoercionTyCon_maybe tc
+ -- CoercionTyCons carry their kinding rule, so we use it here
= if length args >= ar
then splitCoercionKind (rule args)
else pprPanic ("arity/arguments mismatch in coercionKind:")
mkForAllCoercion tv co = ASSERT ( isTyVar tv ) mkForAllTy tv co
mkFunCoercion co1 co2 = mkFunTy co1 co2
+
+-- This smart constructor creates a sym'ed version its argument,
+-- but tries to push the sym's down to the leaves. If we come to
+-- sym tv or sym tycon then we can drop the sym because tv and tycon
+-- are reflexive coercions
mkSymCoercion co
| Just co2 <- splitSymCoercion_maybe co = co2
- | Just (co1, co2) <- splitAppCoercion_maybe co
- -- should make this case better
- = mkAppCoercion (mkSymCoercion co1) (mkSymCoercion co2)
+ -- sym (sym co) --> co
+ | Just (co1, arg_tys) <- splitTyConApp_maybe co
+ , not (isCoercionTyCon co1) = mkTyConApp co1 (map mkSymCoercion arg_tys)
+ -- we can drop the sym for a TyCon
+ -- sym (ty [t1, ..., tn]) --> ty [sym t1, ..., sym tn]
+ | (co1, arg_tys) <- splitAppTys co
+ , isTyVarTy co1 = mkAppTys (maybe_drop co1) (map mkSymCoercion arg_tys)
+ -- sym (tv [t1, ..., tn]) --> tv [sym t1, ..., sym tn]
+ -- if tv type variable
+ -- sym (cv [t1, ..., tn]) --> (sym cv) [sym t1, ..., sym tn]
+ -- if cv is a coercion variable
+ -- fall through if head is a CoercionTyCon
| Just (co1, co2) <- splitTransCoercion_maybe co
+ -- sym (co1 `trans` co2) --> (sym co2) `trans (sym co2)
= mkTransCoercion (mkSymCoercion co2) (mkSymCoercion co1)
| Just (co, ty) <- splitInstCoercion_maybe co
+ -- sym (co @ ty) --> (sym co) @ ty
= mkInstCoercion (mkSymCoercion co) ty
| Just co <- splitLeftCoercion_maybe co
+ -- sym (left co) --> left (sym co)
= mkLeftCoercion (mkSymCoercion co)
| Just co <- splitRightCoercion_maybe co
+ -- sym (right co) --> right (sym co)
= mkRightCoercion (mkSymCoercion co)
+ where
+ maybe_drop (TyVarTy tv)
+ | isCoVar tv = mkCoercion symCoercionTyCon [TyVarTy tv]
+ | otherwise = TyVarTy tv
+ maybe_drop other = other
mkSymCoercion (ForAllTy tv ty) = ForAllTy tv (mkSymCoercion ty)
-- for atomic types and constructors, we can just ignore sym since these
-- are reflexive coercions
| isCoVar tv = mkCoercion symCoercionTyCon [TyVarTy tv]
| otherwise = TyVarTy tv
mkSymCoercion co = mkCoercion symCoercionTyCon [co]
- -- this should not happen but does
-- Smart constructors for left and right
mkLeftCoercion co
splitRightCoercion_maybe other = Nothing
-- Unsafe coercion is not safe, it is used when we know we are dealing with
--- bottom, which is the one case in which it is safe
+-- bottom, which is the one case in which it is safe. It is also used to
+-- implement the unsafeCoerce# primitive.
mkUnsafeCoercion :: Type -> Type -> Coercion
mkUnsafeCoercion ty1 ty2
= mkCoercion unsafeCoercionTyCon [ty1, ty2]
--- make the coercion associated with a newtype
+-- See note [Newtype coercions] in TyCon
mkNewTypeCoercion :: Name -> TyCon -> [TyVar] -> Type -> TyCon
mkNewTypeCoercion name tycon tvs rhs_ty
= ASSERT (length tvs == tyConArity tycon)
mkCoercionTyCon name (tyConArity tycon) rule
where
- rule args = mkCoKind (substTyWith tvs args rhs_ty) (TyConApp tycon args)
+ rule args = mkCoKind (TyConApp tycon args) (substTyWith tvs args rhs_ty)
--------------------------------------
-- Coercion Type Constructors...
symCoercionTyCon, transCoercionTyCon, leftCoercionTyCon, rightCoercionTyCon, instCoercionTyCon :: TyCon
-- Each coercion TyCon is built with the special CoercionTyCon record and
--- carries its won kinding rule. Such CoercionTyCons must be fully applied
+-- carries its own kinding rule. Such CoercionTyCons must be fully applied
-- by any TyConApp in which they are applied, however they may also be over
-- applied (see example above) and the kinding function must deal with this.
symCoercionTyCon =
transCoercionTyCon =
mkCoercionTyCon transCoercionTyConName 2 (mkKindingFun composeCoercionKindsOf)
where
- composeCoercionKindsOf (co1:co2:rest) = (a1, r2, rest)
+ composeCoercionKindsOf (co1:co2:rest) =
+ WARN( not (r1 `coreEqType` a2), text "Strange! Type mismatch in trans coercion, probably a bug")
+ (a1, r2, rest)
where
(a1, r1) = coercionKind co1
(a2, r2) = coercionKind co2
-- this is here to avoid module loops
splitNewTypeRepCo_maybe :: Type -> Maybe (Type, Coercion)
--- Sometimes we want to look through a recursive newtype, and that's what happens here
+-- 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 (substTyWith tvs tys rep_ty, mkTyConApp co_con tys)
where
co_con = maybe (pprPanic "splitNewTypeRepCo_maybe" (ppr tc)) id (newTyConCo tc)
-
splitNewTypeRepCo_maybe other = Nothing
\end{code}
projects / ghc-hetmet.git / blobdiff