typeKind (symCoercion type) :: TyConApp CoercionTyCon{...} [type, type]
\begin{code}
+{-# OPTIONS -w #-}
+-- 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/Commentary/CodingStyle#Warnings
+-- for details
+
module Coercion (
Coercion,
isEqPred, mkEqPred, getEqPredTys, isEqPredTy,
-- Coercion transformations
+ mkCoercion,
mkSymCoercion, mkTransCoercion,
- mkLeftCoercion, mkRightCoercion, mkInstCoercion, mkAppCoercion,
+ mkLeftCoercion, mkRightCoercion, mkRightCoercions,
+ mkInstCoercion, mkAppCoercion,
mkForAllCoercion, mkFunCoercion, mkInstsCoercion, mkUnsafeCoercion,
mkNewTypeCoercion, mkFamInstCoercion, mkAppsCoercion,
- splitNewTypeRepCo_maybe, decomposeCo,
+ splitNewTypeRepCo_maybe, instNewTyCon_maybe, decomposeCo,
unsafeCoercionTyCon, symCoercionTyCon,
transCoercionTyCon, leftCoercionTyCon,
mkSymCoI, mkTransCoI,
mkTyConAppCoI, mkAppTyCoI, mkFunTyCoI,
mkNoteTyCoI, mkForAllTyCoI,
- fromCoI,
- mkClassPPredCoI, mkIParamPredCoI, mkEqPredCoI,
+ fromCoI, fromACo,
+ mkClassPPredCoI, mkIParamPredCoI, mkEqPredCoI
) where
import Outputable
+type Coercion = Type
+type CoercionKind = Kind -- A CoercionKind is always of form (ty1 :=: ty2)
+
------------------------------
decomposeCo :: Arity -> Coercion -> [Coercion]
-- (decomposeCo 3 c) = [right (left (left c)), right (left c), right c]
splitCoercionKind_maybe (PredTy (EqPred ty1 ty2)) = Just (ty1, ty2)
splitCoercionKind_maybe other = Nothing
-type Coercion = Type
-type CoercionKind = Kind -- A CoercionKind is always of form (ty1 :=: ty2)
-
coercionKind :: Coercion -> (Type, Type)
-- c :: (t1 :=: t2)
-- Then (coercionKind c) = (t1,t2)
| Just (co1, co2) <- splitAppCoercion_maybe co = co2
| otherwise = mkCoercion rightCoercionTyCon [co]
+mkRightCoercions n co
+ = go n co []
+ where
+ go n co acc
+ | n > 0
+ = case splitAppCoercion_maybe co of
+ Just (co1,co2) -> go (n-1) co1 (co2:acc)
+ Nothing -> go (n-1) (mkCoercion leftCoercionTyCon [co]) (mkCoercion rightCoercionTyCon [co]:acc)
+ | otherwise
+ = acc
+
mkInstCoercion co ty
| Just (tv,co') <- splitForAllTy_maybe co
= substTyWith [tv] [ty] co' -- (forall a.co) @ ty --> co[ty/a]
where
composeCoercionKindsOf (co1:co2:rest)
= ASSERT( null rest )
- WARN( not (r1 `coreEqType` a2), text "Strange! Type mismatch in trans coercion, probably a bug")
+ WARN( not (r1 `coreEqType` a2),
+ text "Strange! Type mismatch in trans coercion, probably a bug"
+ $$
+ ppr r1 <+> text "=/=" <+> ppr a2)
(a1, r2)
where
(a1, r1) = coercionKind co1
, Just (ty_fun1, ty_arg1) <- splitAppTy_maybe ty1
, Just (ty_fun2, ty_arg2) <- splitAppTy_maybe ty2
= ((ty_fun1, ty_fun2),(ty_arg1, ty_arg2))
+splitCoercionKindOf co
+ = pprPanic "Coercion.splitCoercionKindOf"
+ (ppr co $$ ppr (coercionKindPredTy co))
instCoercionTyCon
= mkCoercionTyCon instCoercionTyConName 2 instCoercionKind
+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}
-- CoercionI smart constructors
-- lifted smart constructors of ordinary coercions
-
\begin{code}
-
-- CoercionI is either
-- (a) proper coercion
-- (b) the identity coercion
isIdentityCoercion IdCo = True
isIdentityCoercion _ = False
+allIdCos :: [CoercionI] -> Bool
+allIdCos = all isIdentityCoercion
+
+zipCoArgs :: [CoercionI] -> [Type] -> [Coercion]
+zipCoArgs cois tys = zipWith fromCoI cois tys
+
+fromCoI :: CoercionI -> Type -> Type
+fromCoI IdCo ty = ty -- Identity coercion represented
+fromCoI (ACo co) ty = co -- by the type itself
+
mkSymCoI :: CoercionI -> CoercionI
mkSymCoI IdCo = IdCo
mkSymCoI (ACo co) = ACo $ mkCoercion symCoercionTyCon [co]
mkTransCoI (ACo co1) (ACo co2) = ACo $ mkTransCoercion co1 co2
mkTyConAppCoI :: TyCon -> [Type] -> [CoercionI] -> CoercionI
-mkTyConAppCoI tyCon tys cois =
- let (anyAcon,co_args) = f tys cois
- in if anyAcon
- then ACo (TyConApp tyCon co_args)
- else IdCo
- where
- f [] [] = (False,[])
- f (x:xs) (y:ys) =
- let (b,cos) = f xs ys
- in case y of
- IdCo -> (b,x:cos)
- ACo co -> (True,co:cos)
+mkTyConAppCoI tyCon tys cois
+ | allIdCos cois = IdCo
+ | otherwise = ACo (TyConApp tyCon (zipCoArgs cois tys))
mkAppTyCoI :: Type -> CoercionI -> Type -> CoercionI -> CoercionI
mkAppTyCoI ty1 IdCo ty2 IdCo = IdCo
mkForAllTyCoI _ IdCo = IdCo
mkForAllTyCoI tv (ACo co) = ACo $ ForAllTy tv co
-fromCoI IdCo ty = ty
-fromCoI (ACo co) ty = co
+fromACo :: CoercionI -> Coercion
+fromACo (ACo co) = co
mkClassPPredCoI :: Class -> [Type] -> [CoercionI] -> CoercionI
-mkClassPPredCoI cls tys cois =
- let (anyAcon,co_args) = f tys cois
- in if anyAcon
- then ACo $ PredTy $ ClassP cls co_args
- else IdCo
- where
- f [] [] = (False,[])
- f (x:xs) (y:ys) =
- let (b,cos) = f xs ys
- in case y of
- IdCo -> (b,x:cos)
- ACo co -> (True,co:cos)
+-- mkClassPPredCoI cls tys cois = coi
+-- coi : PredTy (cls tys) ~ predTy (cls (tys `cast` cois))
+mkClassPPredCoI cls tys cois
+ | allIdCos cois = IdCo
+ | otherwise = ACo $ PredTy $ ClassP cls (zipCoArgs cois tys)
mkIParamPredCoI :: (IPName Name) -> CoercionI -> CoercionI
+-- Similar invariant to mkclassPPredCoI
mkIParamPredCoI ipn IdCo = IdCo
mkIParamPredCoI ipn (ACo co) = ACo $ PredTy $ IParam ipn co
mkEqPredCoI :: Type -> CoercionI -> Type -> CoercionI -> CoercionI
+-- Similar invariant to mkclassPPredCoI
mkEqPredCoI _ IdCo _ IdCo = IdCo
mkEqPredCoI ty1 IdCo _ (ACo co2) = ACo $ PredTy $ EqPred ty1 co2
mkEqPredCoI ty1 (ACo co1) ty2 coi2 = ACo $ PredTy $ EqPred co1 (fromCoI coi2 ty2)
-
\end{code}