X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FCoercion.lhs;h=83a5af341cacc4c33acb5a8a390b2852b47ee2b8;hb=bcadca676448e38427b910bad5d7063f948a99c8;hp=674e2a70bdd3c1d423291669d6a4e20e5ac14c93;hpb=30c122df62ec75f9ed7f392f24c2925675bf1d06;p=ghc-hetmet.git diff --git a/compiler/types/Coercion.lhs b/compiler/types/Coercion.lhs index 674e2a7..83a5af3 100644 --- a/compiler/types/Coercion.lhs +++ b/compiler/types/Coercion.lhs @@ -1,16 +1,7 @@ -% +T% % (c) The University of Glasgow 2006 % -Module for type coercions, as in System FC. - -Coercions are represented as types, and their kinds tell what types the -coercion works on. - -The coercion kind constructor is a special TyCon that must always be saturated - - typeKind (symCoercion type) :: TyConApp CoercionTyCon{...} [type, type] - \begin{code} {-# OPTIONS -fno-warn-incomplete-patterns #-} -- The above warning supression flag is a temporary kludge. @@ -19,35 +10,48 @@ The coercion kind constructor is a special TyCon that must always be saturated -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings -- for details +-- | Module for type coercions, as used in System FC. See 'CoreSyn.Expr' for +-- more on System FC and how coercions fit into it. +-- +-- Coercions are represented as types, and their kinds tell what types the +-- coercion works on. The coercion kind constructor is a special TyCon that must always be saturated, like so: +-- +-- > typeKind (symCoercion type) :: TyConApp CoercionTyCon{...} [type, type] module Coercion ( + -- * Main data type Coercion, - mkCoKind, mkReflCoKind, splitCoercionKind_maybe, splitCoercionKind, - coercionKind, coercionKinds, coercionKindPredTy, + mkCoKind, mkReflCoKind, coVarKind, + coercionKind, coercionKinds, isIdentityCoercion, - -- Equality predicates + -- ** Equality predicates isEqPred, mkEqPred, getEqPredTys, isEqPredTy, - -- Coercion transformations + -- ** Coercion transformations mkCoercion, mkSymCoercion, mkTransCoercion, mkLeftCoercion, mkRightCoercion, mkRightCoercions, - mkInstCoercion, mkAppCoercion, - mkForAllCoercion, mkFunCoercion, mkInstsCoercion, mkUnsafeCoercion, + mkInstCoercion, mkAppCoercion, mkTyConCoercion, mkFunCoercion, + mkForAllCoercion, mkInstsCoercion, mkUnsafeCoercion, mkNewTypeCoercion, mkFamInstCoercion, mkAppsCoercion, + mkCsel1Coercion, mkCsel2Coercion, mkCselRCoercion, splitNewTypeRepCo_maybe, instNewTyCon_maybe, decomposeCo, unsafeCoercionTyCon, symCoercionTyCon, transCoercionTyCon, leftCoercionTyCon, rightCoercionTyCon, instCoercionTyCon, -- needed by TysWiredIn + csel1CoercionTyCon, csel2CoercionTyCon, cselRCoercionTyCon, + + -- ** Optimisation + optCoercion, - -- Comparison + -- ** Comparison coreEqCoercion, - -- CoercionI + -- * CoercionI CoercionI(..), - isIdentityCoercion, + isIdentityCoI, mkSymCoI, mkTransCoI, mkTyConAppCoI, mkAppTyCoI, mkFunTyCoI, mkForAllTyCoI, @@ -64,22 +68,26 @@ import TyCon import Class import Var import Name -import OccName import PrelNames import Util -import Unique import BasicTypes import Outputable import FastString +-- | A 'Coercion' represents a 'Type' something should be coerced to. type Coercion = Type -type CoercionKind = Kind -- A CoercionKind is always of form (ty1 :=: ty2) + +-- | A 'CoercionKind' is always of form @ty1 ~ ty2@ and indicates the +-- types that a 'Coercion' will work on. +type CoercionKind = Kind ------------------------------ + +-- | This breaks a 'Coercion' with 'CoercionKind' @T A B C ~ T D E F@ into +-- a list of 'Coercion's of kinds @A ~ D@, @B ~ E@ and @E ~ F@. Hence: +-- +-- > decomposeCo 3 c = [right (left (left c)), right (left c), right c] 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 @@ -92,36 +100,50 @@ decomposeCo n co ------------------------------------------------------- -- and some coercion kind stuff +coVarKind :: CoVar -> (Type,Type) +-- c :: t1 ~ t2 +coVarKind cv = splitCoVarKind (tyVarKind cv) + +-- | Take a 'CoercionKind' apart into the two types it relates: see also 'mkCoKind'. +-- Panics if the argument is not a valid 'CoercionKind' +splitCoVarKind :: Kind -> (Type, Type) +splitCoVarKind co | Just co' <- kindView co = splitCoVarKind co' +splitCoVarKind (PredTy (EqPred ty1 ty2)) = (ty1, ty2) + +-- | Makes a 'CoercionKind' from two types: the types whose equality is proven by the relevant 'Coercion' +mkCoKind :: Type -> Type -> CoercionKind +mkCoKind ty1 ty2 = PredTy (EqPred ty1 ty2) + +-- | (mkCoPredTy s t r) produces the type: (s~t) => r +mkCoPredTy :: Type -> Type -> Type -> Type +mkCoPredTy s t r = ForAllTy (mkWildCoVar (mkCoKind s t)) r + +-- | Tests whether a type is just a type equality predicate isEqPredTy :: Type -> Bool isEqPredTy (PredTy pred) = isEqPred pred isEqPredTy _ = False +-- | Creates a type equality predicate mkEqPred :: (Type, Type) -> PredType mkEqPred (ty1, ty2) = EqPred ty1 ty2 +-- | Splits apart a type equality predicate, if the supplied 'PredType' is one. +-- Panics otherwise getEqPredTys :: PredType -> (Type,Type) getEqPredTys (EqPred ty1 ty2) = (ty1, ty2) getEqPredTys other = pprPanic "getEqPredTys" (ppr other) -mkCoKind :: Type -> Type -> CoercionKind -mkCoKind ty1 ty2 = PredTy (EqPred ty1 ty2) - +-- | Create a reflexive 'CoercionKind' that asserts that a type can be coerced to itself mkReflCoKind :: Type -> CoercionKind mkReflCoKind ty = mkCoKind ty ty -splitCoercionKind :: CoercionKind -> (Type, Type) -splitCoercionKind co | Just co' <- kindView co = splitCoercionKind co' -splitCoercionKind (PredTy (EqPred ty1 ty2)) = (ty1, ty2) - -splitCoercionKind_maybe :: Kind -> Maybe (Type, Type) -splitCoercionKind_maybe co | Just co' <- kindView co = splitCoercionKind_maybe co' -splitCoercionKind_maybe (PredTy (EqPred ty1 ty2)) = Just (ty1, ty2) -splitCoercionKind_maybe _ = Nothing - +-- | If it is the case that +-- +-- > c :: (t1 ~ t2) +-- +-- i.e. the kind of @c@ is a 'CoercionKind' relating @t1@ and @t2@, then @coercionKind c = (t1, t2)@. coercionKind :: Coercion -> (Type, Type) --- c :: (t1 :=: t2) --- Then (coercionKind c) = (t1,t2) -coercionKind ty@(TyVarTy a) | isCoVar a = splitCoercionKind (tyVarKind a) +coercionKind ty@(TyVarTy a) | isCoVar a = coVarKind a | otherwise = (ty, ty) coercionKind (AppTy ty1 ty2) = let (t1, t2) = coercionKind ty1 @@ -142,13 +164,40 @@ coercionKind (FunTy ty1 ty2) = let (t1, t2) = coercionKind ty1 (s1, s2) = coercionKind ty2 in (mkFunTy t1 s1, mkFunTy t2 s2) -coercionKind (ForAllTy tv ty) + +coercionKind (ForAllTy tv ty) + | isCoVar tv +-- c1 :: s1~s2 c2 :: t1~t2 c3 :: r1~r2 +-- ---------------------------------------------- +-- c1~c2 => c3 :: (s1~t1) => r1 ~ (s2~t2) => r2 +-- or +-- forall (_:c1~c2) + = let (c1,c2) = coVarKind tv + (s1,s2) = coercionKind c1 + (t1,t2) = coercionKind c2 + (r1,r2) = coercionKind ty + in + (mkCoPredTy s1 t1 r1, mkCoPredTy s2 t2 r2) + + | otherwise +-- c1 :: s1~s2 c2 :: t1~t2 c3 :: r1~r2 +-- ---------------------------------------------- +-- forall a:k. c :: forall a:k. t1 ~ forall a:k. t2 = let (ty1, ty2) = coercionKind ty in (ForAllTy tv ty1, ForAllTy tv ty2) + coercionKind (PredTy (EqPred c1 c2)) - = let k1 = coercionKindPredTy c1 + = pprTrace "coercionKind" (pprEqPred (c1,c2)) $ + let k1 = coercionKindPredTy c1 k2 = coercionKindPredTy c2 in (k1,k2) + -- These should not show up in coercions at all + -- becuase they are in the form of for-alls + where + coercionKindPredTy c = let (t1, t2) = coercionKind c in mkCoKind t1 t2 + + + coercionKind (PredTy (ClassP cl args)) = let (lArgs, rArgs) = coercionKinds args in (PredTy (ClassP cl lArgs), PredTy (ClassP cl rArgs)) @@ -156,37 +205,67 @@ coercionKind (PredTy (IParam name ty)) = let (ty1, ty2) = coercionKind ty in (PredTy (IParam name ty1), PredTy (IParam name ty2)) -coercionKindPredTy :: Coercion -> CoercionKind -coercionKindPredTy c = let (t1, t2) = coercionKind c in mkCoKind t1 t2 - +-- | Apply 'coercionKind' to multiple 'Coercion's coercionKinds :: [Coercion] -> ([Type], [Type]) coercionKinds tys = unzip $ map coercionKind tys ------------------------------------- --- Coercion kind and type mk's --- (make saturated TyConApp CoercionTyCon{...} args) +isIdentityCoercion :: Coercion -> Bool +isIdentityCoercion co + = case coercionKind co of + (t1,t2) -> t1 `coreEqType` t2 +\end{code} + +%************************************************************************ +%* * + Building coercions +%* * +%************************************************************************ + +Coercion kind and type mk's (make saturated TyConApp CoercionTyCon{...} args) +\begin{code} +-- | Make a coercion from the specified coercion 'TyCon' and the 'Type' arguments to +-- that coercion. Try to use the @mk*Coercion@ family of functions instead of using this function +-- if possible mkCoercion :: TyCon -> [Type] -> Coercion mkCoercion coCon args = ASSERT( tyConArity coCon == length args ) TyConApp coCon args -mkAppCoercion, mkFunCoercion, mkTransCoercion, mkInstCoercion :: Coercion -> Coercion -> Coercion -mkSymCoercion, mkLeftCoercion, mkRightCoercion :: Coercion -> Coercion -mkAppsCoercion, mkInstsCoercion :: Coercion -> [Coercion] -> Coercion -mkForAllCoercion :: Var -> Coercion -> Coercion +-- | Apply a 'Coercion' to another 'Coercion', which is presumably a +-- 'Coercion' constructor of some kind +mkAppCoercion :: Coercion -> Coercion -> Coercion +mkAppCoercion co1 co2 = mkAppTy co1 co2 + +-- | Applies multiple 'Coercion's to another 'Coercion', from left to right. +-- See also 'mkAppCoercion' +mkAppsCoercion :: Coercion -> [Coercion] -> Coercion +mkAppsCoercion co1 tys = foldl mkAppTy co1 tys + +-- | Apply a type constructor to a list of coercions. +mkTyConCoercion :: TyCon -> [Coercion] -> Coercion +mkTyConCoercion con cos = mkTyConApp con cos + +-- | Make a function 'Coercion' between two other 'Coercion's +mkFunCoercion :: Coercion -> Coercion -> Coercion +mkFunCoercion co1 co2 = mkFunTy co1 co2 -mkAppCoercion co1 co2 = mkAppTy co1 co2 -mkAppsCoercion co1 tys = foldl mkAppTy co1 tys +-- | Make a 'Coercion' which binds a variable within an inner 'Coercion' +mkForAllCoercion :: Var -> Coercion -> Coercion -- note that a TyVar should be used here, not a CoVar (nor a TcTyVar) 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 :: Coercion -> Coercion +-- ^ Create a symmetric version of the given 'Coercion' that asserts equality +-- between the same types but in the other "direction", so a kind of @t1 ~ t2@ +-- becomes the kind @t2 ~ t1@. +-- +-- This function attempts to simplify the generated 'Coercion' by removing +-- redundant applications of @sym@. This is done by pushing this new @sym@ +-- down into the 'Coercion' and exploiting the fact that @sym (sym co) = co@. mkSymCoercion co | Just co' <- coreView co = mkSymCoercion co' @@ -222,6 +301,12 @@ mkSymCoercion (TyVarTy tv) ------------------------------- -- ToDo: we should be cleverer about transitivity + +mkTransCoercion :: Coercion -> Coercion -> Coercion +-- ^ Create a new 'Coercion' by exploiting transitivity on the two given 'Coercion's. +-- +-- This function attempts to simplify the generated 'Coercion' by exploiting the fact that +-- @sym g `trans` g = id@. mkTransCoercion g1 g2 -- sym g `trans` g = id | (t1,_) <- coercionKind g1 , (_,t2) <- coercionKind g2 @@ -234,15 +319,29 @@ mkTransCoercion g1 g2 -- sym g `trans` g = id ------------------------------- -- Smart constructors for left and right + +mkLeftCoercion :: Coercion -> Coercion +-- ^ From an application 'Coercion' build a 'Coercion' that asserts the equality of +-- the "functions" on either side of the type equality. So if @c@ has kind @f x ~ g y@ then: +-- +-- > mkLeftCoercion c :: f ~ g mkLeftCoercion co | Just (co', _) <- splitAppCoercion_maybe co = co' | otherwise = mkCoercion leftCoercionTyCon [co] +mkRightCoercion :: Coercion -> Coercion +-- ^ From an application 'Coercion' build a 'Coercion' that asserts the equality of +-- the "arguments" on either side of the type equality. So if @c@ has kind @f x ~ g y@ then: +-- +-- > mkLeftCoercion c :: x ~ y mkRightCoercion co | Just (_, co2) <- splitAppCoercion_maybe co = co2 | otherwise = mkCoercion rightCoercionTyCon [co] mkRightCoercions :: Int -> Coercion -> [Coercion] +-- ^ As 'mkRightCoercion', but finds the 'Coercion's available on the right side of @n@ +-- nested application 'Coercion's, manufacturing new left or right cooercions as necessary +-- if suffficiently many are not directly available. mkRightCoercions n co = go n co [] where @@ -254,12 +353,24 @@ mkRightCoercions n co | otherwise = acc + +mkCsel1Coercion, mkCsel2Coercion, mkCselRCoercion :: Coercion -> Coercion +mkCsel1Coercion co = mkCoercion csel1CoercionTyCon [co] +mkCsel2Coercion co = mkCoercion csel2CoercionTyCon [co] +mkCselRCoercion co = mkCoercion cselRCoercionTyCon [co] + +------------------------------- +mkInstCoercion :: Coercion -> Type -> Coercion +-- ^ Instantiates a 'Coercion' with a 'Type' argument. If possible, it immediately performs +-- the resulting beta-reduction, otherwise it creates a suspended instantiation. mkInstCoercion co ty | Just (tv,co') <- splitForAllTy_maybe co = substTyWith [tv] [ty] co' -- (forall a.co) @ ty --> co[ty/a] | otherwise = mkCoercion instCoercionTyCon [co, ty] +mkInstsCoercion :: Coercion -> [Type] -> Coercion +-- ^ As 'mkInstCoercion', but instantiates the coercion with a number of type arguments, left-to-right mkInstsCoercion co tys = foldl mkInstCoercion co tys {- @@ -272,8 +383,8 @@ splitSymCoercion_maybe co = Nothing -} splitAppCoercion_maybe :: Coercion -> Maybe (Coercion, Coercion) --- Splits a coercion application, being careful *not* to split (left c), etc --- which are really sytactic constructs, not applications +-- ^ Splits a coercion application, being careful *not* to split @left c@ etc. +-- This is because those are really syntactic constructs, not applications splitAppCoercion_maybe co | Just co' <- coreView co = splitAppCoercion_maybe co' splitAppCoercion_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2) splitAppCoercion_maybe (AppTy ty1 ty2) = Just (ty1, ty2) @@ -318,15 +429,20 @@ splitRightCoercion_maybe (TyConApp tc [co]) splitRightCoercion_maybe other = Nothing -} --- Unsafe coercion is not safe, it is used when we know we are dealing with --- bottom, which is one case in which it is safe. It is also used to --- implement the unsafeCoerce# primitive. +-- | Manufacture a coercion from this air. Needless to say, this is not usually safe, +-- but it is used when we know we are dealing with bottom, which is one case in which +-- it is safe. This is also used implement the @unsafeCoerce#@ primitive. mkUnsafeCoercion :: Type -> Type -> Coercion mkUnsafeCoercion ty1 ty2 = mkCoercion unsafeCoercionTyCon [ty1, ty2] -- See note [Newtype coercions] in TyCon + +-- | Create a coercion suitable for the given 'TyCon'. The 'Name' should be that of a +-- new coercion 'TyCon', the 'TyVar's the arguments expected by the @newtype@ and the +-- type the appropriate right hand side of the @newtype@, with the free variables +-- a subset of those 'TyVar's. mkNewTypeCoercion :: Name -> TyCon -> [TyVar] -> Type -> TyCon mkNewTypeCoercion name tycon tvs rhs_ty = mkCoercionTyCon name co_con_arity rule @@ -336,40 +452,51 @@ mkNewTypeCoercion name tycon tvs rhs_ty rule args = ASSERT( co_con_arity == length args ) (TyConApp tycon args, substTyWith tvs args rhs_ty) --- Coercion identifying a data/newtype/synonym representation type and its --- family instance. It has the form `Co tvs :: F ts :=: R tvs', where `Co' is --- the coercion tycon built here, `F' the family tycon and `R' the (derived) +-- | Create a coercion identifying a @data@, @newtype@ or @type@ representation type +-- and its family instance. It has the form @Co tvs :: F ts ~ R tvs@, where @Co@ is +-- the coercion tycon built here, @F@ the family tycon and @R@ the (derived) -- representation tycon. --- -mkFamInstCoercion :: Name -- unique name for the coercion tycon - -> [TyVar] -- type parameters of the coercion (`tvs') - -> TyCon -- family tycon (`F') - -> [Type] -- type instance (`ts') - -> TyCon -- representation tycon (`R') - -> TyCon -- => coercion tycon (`Co') +mkFamInstCoercion :: Name -- ^ Unique name for the coercion tycon + -> [TyVar] -- ^ Type parameters of the coercion (@tvs@) + -> TyCon -- ^ Family tycon (@F@) + -> [Type] -- ^ Type instance (@ts@) + -> TyCon -- ^ Representation tycon (@R@) + -> TyCon -- ^ Coercion tycon (@Co@) mkFamInstCoercion name tvs family instTys rep_tycon = mkCoercionTyCon name coArity rule where coArity = length tvs rule args = (substTyWith tvs args $ -- with sigma = [tys/tvs], TyConApp family instTys, -- sigma (F ts) - TyConApp rep_tycon args) -- :=: R tys + TyConApp rep_tycon args) -- ~ R tys +\end{code} --------------------------------------- --- Coercion Type Constructors... --- Example. The coercion ((sym c) (sym d) (sym e)) --- will be represented by (TyConApp sym [c, sym d, sym e]) --- If sym c :: p1=q1 --- sym d :: p2=q2 --- sym e :: p3=q3 --- then ((sym c) (sym d) (sym e)) :: (p1 p2 p3)=(q1 q2 q3) +%************************************************************************ +%* * + Coercion Type Constructors +%* * +%************************************************************************ -symCoercionTyCon, transCoercionTyCon, leftCoercionTyCon, rightCoercionTyCon, instCoercionTyCon, unsafeCoercionTyCon :: TyCon +Example. The coercion ((sym c) (sym d) (sym e)) +will be represented by (TyConApp sym [c, sym d, sym e]) +If sym c :: p1=q1 + sym d :: p2=q2 + sym e :: p3=q3 +then ((sym c) (sym d) (sym e)) :: (p1 p2 p3)=(q1 q2 q3) + +\begin{code} +-- | Coercion type constructors: avoid using these directly and instead use +-- the @mk*Coercion@ and @split*Coercion@ family of functions if possible. +-- -- Each coercion TyCon is built with the special CoercionTyCon record and -- 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, leftCoercionTyCon, + rightCoercionTyCon, instCoercionTyCon, unsafeCoercionTyCon, + csel1CoercionTyCon, csel2CoercionTyCon, cselRCoercionTyCon :: TyCon + symCoercionTyCon = mkCoercionTyCon symCoercionTyConName 1 flipCoercionKindOf where @@ -382,43 +509,42 @@ transCoercionTyCon = where composeCoercionKindsOf (co1:co2:rest) = ASSERT( null rest ) - WARN( not (r1 `coreEqType` a2), + WARN( not (r1 `coreEqType` a2), text "Strange! Type mismatch in trans coercion, probably a bug" $$ - ppr r1 <+> text "=/=" <+> ppr a2) + _err_stuff ) (a1, r2) where (a1, r1) = coercionKind co1 (a2, r2) = coercionKind co2 -leftCoercionTyCon = - mkCoercionTyCon leftCoercionTyConName 1 leftProjectCoercionKindOf - where - leftProjectCoercionKindOf (co:rest) = ASSERT( null rest ) (ty1, ty2) - where - (ty1,ty2) = fst (splitCoercionKindOf co) + _err_stuff = vcat [ text "co1:" <+> ppr co1 + , text "co1 kind left:" <+> ppr a1 + , text "co1 kind right:" <+> ppr r1 + , text "co2:" <+> ppr co2 + , text "co2 kind left:" <+> ppr a2 + , text "co2 kind right:" <+> ppr r2 ] -rightCoercionTyCon = - mkCoercionTyCon rightCoercionTyConName 1 rightProjectCoercionKindOf - where - rightProjectCoercionKindOf (co:rest) = ASSERT( null rest ) (ty1, ty2) - where - (ty1,ty2) = snd (splitCoercionKindOf co) +--------------------------------------------------- +leftCoercionTyCon = mkCoercionTyCon leftCoercionTyConName 1 (fst . decompLR) +rightCoercionTyCon = mkCoercionTyCon rightCoercionTyConName 1 (snd . decompLR) -splitCoercionKindOf :: Type -> ((Type,Type), (Type,Type)) +decompLR :: [Type] -> ((Type,Type), (Type,Type)) -- Helper for left and right. Finds coercion kind of its input and -- returns the left and right projections of the coercion... -- --- if c :: t1 s1 :=: t2 s2 then splitCoercionKindOf c = ((t1, t2), (s1, s2)) -splitCoercionKindOf co - | Just (ty1, ty2) <- splitCoercionKind_maybe (coercionKindPredTy co) +-- if c :: t1 s1 ~ t2 s2 then splitCoercionKindOf c = ((t1, t2), (s1, s2)) +decompLR (co : rest) + | (ty1, ty2) <- coercionKind co , Just (ty_fun1, ty_arg1) <- splitAppTy_maybe ty1 , Just (ty_fun2, ty_arg2) <- splitAppTy_maybe ty2 - = ((ty_fun1, ty_fun2),(ty_arg1, ty_arg2)) -splitCoercionKindOf co - = pprPanic "Coercion.splitCoercionKindOf" - (ppr co $$ ppr (coercionKindPredTy co)) + = ASSERT( null rest) + ((ty_fun1, ty_fun2),(ty_arg1, ty_arg2)) +decompLR cos + = pprPanic "Coercion.decompLR" + (ppr cos $$ vcat (map (pprEqPred .coercionKind) cos)) +--------------------------------------------------- instCoercionTyCon = mkCoercionTyCon instCoercionTyConName 2 instCoercionKind where @@ -430,32 +556,75 @@ instCoercionTyCon (instantiateCo t1 ty, instantiateCo t2 ty) where (t1, t2) = coercionKind co1 +--------------------------------------------------- unsafeCoercionTyCon = mkCoercionTyCon unsafeCoercionTyConName 2 unsafeCoercionKind where unsafeCoercionKind (ty1:ty2:rest) = ASSERT( null rest ) (ty1,ty2) +--------------------------------------------------- +-- The csel* family +-- If co :: (s1~t1 => r1) ~ (s2~t2 => r2) +-- Then csel1 co :: s1 ~ s2 +-- csel2 co :: t1 ~ t2 +-- cselR co :: r1 ~ r2 + +csel1CoercionTyCon = mkCoercionTyCon csel1CoercionTyConName 1 (fstOf3 . decompCsel) +csel2CoercionTyCon = mkCoercionTyCon csel2CoercionTyConName 1 (sndOf3 . decompCsel) +cselRCoercionTyCon = mkCoercionTyCon cselRCoercionTyConName 1 (thirdOf3 . decompCsel) + +decompCsel :: [Coercion] -> ((Type,Type), (Type,Type), (Type,Type)) +decompCsel (co : rest) + | (ty1,ty2) <- coercionKind co + , Just (cv1, r1) <- splitForAllTy_maybe ty1 + , Just (cv2, r2) <- splitForAllTy_maybe ty2 + , (s1,t1) <- ASSERT( isCoVar cv1) coVarKind cv1 + , (s2,t2) <- ASSERT( isCoVar cv1) coVarKind cv2 + = ASSERT( null rest ) + ((s1,s2), (t1,t2), (r1,r2)) +decompCsel other = pprPanic "decompCsel" (ppr other) + +fstOf3 :: (a,b,c) -> a +sndOf3 :: (a,b,c) -> b +thirdOf3 :: (a,b,c) -> c +fstOf3 (a,_,_) = a +sndOf3 (_,b,_) = b +thirdOf3 (_,_,c) = c + -------------------------------------- --- ...and their names +-- Their Names + +transCoercionTyConName, symCoercionTyConName, leftCoercionTyConName, + rightCoercionTyConName, instCoercionTyConName, unsafeCoercionTyConName, + csel1CoercionTyConName, csel2CoercionTyConName, cselRCoercionTyConName :: Name + +transCoercionTyConName = mkCoConName (fsLit "trans") transCoercionTyConKey transCoercionTyCon +symCoercionTyConName = mkCoConName (fsLit "sym") symCoercionTyConKey symCoercionTyCon +leftCoercionTyConName = mkCoConName (fsLit "left") leftCoercionTyConKey leftCoercionTyCon +rightCoercionTyConName = mkCoConName (fsLit "right") rightCoercionTyConKey rightCoercionTyCon +instCoercionTyConName = mkCoConName (fsLit "inst") instCoercionTyConKey instCoercionTyCon +csel1CoercionTyConName = mkCoConName (fsLit "csel1") csel1CoercionTyConKey csel1CoercionTyCon +csel2CoercionTyConName = mkCoConName (fsLit "csel2") csel2CoercionTyConKey csel2CoercionTyCon +cselRCoercionTyConName = mkCoConName (fsLit "cselR") cselRCoercionTyConKey cselRCoercionTyCon +unsafeCoercionTyConName = mkCoConName (fsLit "CoUnsafe") unsafeCoercionTyConKey unsafeCoercionTyCon mkCoConName :: FastString -> Unique -> TyCon -> Name -mkCoConName occ key coCon = mkWiredInName gHC_PRIM (mkOccNameFS tcName occ) +mkCoConName occ key coCon = mkWiredInName gHC_PRIM (mkTcOccFS occ) key (ATyCon coCon) BuiltInSyntax - -transCoercionTyConName, symCoercionTyConName, leftCoercionTyConName, rightCoercionTyConName, instCoercionTyConName, unsafeCoercionTyConName :: Name - -transCoercionTyConName = mkCoConName FSLIT("trans") transCoercionTyConKey transCoercionTyCon -symCoercionTyConName = mkCoConName FSLIT("sym") symCoercionTyConKey symCoercionTyCon -leftCoercionTyConName = mkCoConName FSLIT("left") leftCoercionTyConKey leftCoercionTyCon -rightCoercionTyConName = mkCoConName FSLIT("right") rightCoercionTyConKey rightCoercionTyCon -instCoercionTyConName = mkCoConName FSLIT("inst") instCoercionTyConKey instCoercionTyCon -unsafeCoercionTyConName = mkCoConName FSLIT("CoUnsafe") unsafeCoercionTyConKey unsafeCoercionTyCon +\end{code} +%************************************************************************ +%* * + Newtypes +%* * +%************************************************************************ +\begin{code} instNewTyCon_maybe :: TyCon -> [Type] -> Maybe (Type, CoercionI) --- instNewTyCon_maybe T ts --- = Just (rep_ty, co) if co : T ts ~ rep_ty +-- ^ If @co :: T ts ~ rep_ty@ then: +-- +-- > instNewTyCon_maybe T ts = Just (rep_ty, co) instNewTyCon_maybe tc tys | Just (tvs, ty, mb_co_tc) <- unwrapNewTyCon_maybe tc = ASSERT( tys `lengthIs` tyConArity tc ) @@ -468,12 +637,14 @@ instNewTyCon_maybe tc tys -- 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 +-- ^ Sometimes we want to look through a @newtype@ and get its associated coercion. +-- This function only strips *one layer* of @newtype@ off, so the caller will usually call +-- itself recursively. Furthermore, this function should only be applied to types of kind @*@, +-- hence the newtype is always saturated. If @co : ty ~ ty'@ then: +-- +-- > splitNewTypeRepCo_maybe ty = Just (ty', co) +-- +-- The function returns @Nothing@ for non-@newtypes@ or fully-transparent @newtype@s. splitNewTypeRepCo_maybe ty | Just ty' <- coreView ty = splitNewTypeRepCo_maybe ty' splitNewTypeRepCo_maybe (TyConApp tc tys) @@ -485,87 +656,215 @@ splitNewTypeRepCo_maybe (TyConApp tc tys) splitNewTypeRepCo_maybe _ = Nothing -------------------------------------- --- Syntactic equality of coercions - +-- | Determines syntactic equality of coercions coreEqCoercion :: Coercion -> Coercion -> Bool coreEqCoercion = coreEqType \end{code} +%************************************************************************ +%* * + CoercionI and its constructors +%* * +%************************************************************************ + -------------------------------------- -- CoercionI smart constructors -- lifted smart constructors of ordinary coercions \begin{code} - -- CoercionI is either - -- (a) proper coercion - -- (b) the identity coercion +-- | 'CoercionI' represents a /lifted/ ordinary 'Coercion', in that it +-- can represent either one of: +-- +-- 1. A proper 'Coercion' +-- +-- 2. The identity coercion data CoercionI = IdCo | ACo Coercion -isIdentityCoercion :: CoercionI -> Bool -isIdentityCoercion IdCo = True -isIdentityCoercion _ = False +instance Outputable CoercionI where + ppr IdCo = ptext (sLit "IdCo") + ppr (ACo co) = ppr co + +isIdentityCoI :: CoercionI -> Bool +isIdentityCoI IdCo = True +isIdentityCoI _ = False -allIdCos :: [CoercionI] -> Bool -allIdCos = all isIdentityCoercion +-- | Tests whether all the given 'CoercionI's represent the identity coercion +allIdCoIs :: [CoercionI] -> Bool +allIdCoIs = all isIdentityCoI +-- | For each 'CoercionI' in the input list, return either the 'Coercion' it +-- contains or the corresponding 'Type' from the other list zipCoArgs :: [CoercionI] -> [Type] -> [Coercion] zipCoArgs cois tys = zipWith fromCoI cois tys +-- | Return either the 'Coercion' contained within the 'CoercionI' or the given +-- 'Type' if the 'CoercionI' is the identity 'Coercion' fromCoI :: CoercionI -> Type -> Type fromCoI IdCo ty = ty -- Identity coercion represented fromCoI (ACo co) _ = co -- by the type itself +-- | Smart constructor for @sym@ on 'CoercionI', see also 'mkSymCoercion' mkSymCoI :: CoercionI -> CoercionI mkSymCoI IdCo = IdCo mkSymCoI (ACo co) = ACo $ mkCoercion symCoercionTyCon [co] -- the smart constructor -- is too smart with tyvars +-- | Smart constructor for @trans@ on 'CoercionI', see also 'mkTransCoercion' mkTransCoI :: CoercionI -> CoercionI -> CoercionI mkTransCoI IdCo aco = aco mkTransCoI aco IdCo = aco mkTransCoI (ACo co1) (ACo co2) = ACo $ mkTransCoercion co1 co2 +-- | Smart constructor for type constructor application on 'CoercionI', see also 'mkAppCoercion' mkTyConAppCoI :: TyCon -> [Type] -> [CoercionI] -> CoercionI mkTyConAppCoI tyCon tys cois - | allIdCos cois = IdCo - | otherwise = ACo (TyConApp tyCon (zipCoArgs cois tys)) + | allIdCoIs cois = IdCo + | otherwise = ACo (TyConApp tyCon (zipCoArgs cois tys)) +-- | Smart constructor for honest-to-god 'Coercion' application on 'CoercionI', see also 'mkAppCoercion' mkAppTyCoI :: Type -> CoercionI -> Type -> CoercionI -> CoercionI mkAppTyCoI _ IdCo _ IdCo = IdCo mkAppTyCoI ty1 coi1 ty2 coi2 = ACo $ AppTy (fromCoI coi1 ty1) (fromCoI coi2 ty2) +-- | Smart constructor for function-'Coercion's on 'CoercionI', see also 'mkFunCoercion' mkFunTyCoI :: Type -> CoercionI -> Type -> CoercionI -> CoercionI mkFunTyCoI _ IdCo _ IdCo = IdCo mkFunTyCoI ty1 coi1 ty2 coi2 = ACo $ FunTy (fromCoI coi1 ty1) (fromCoI coi2 ty2) +-- | Smart constructor for quantified 'Coercion's on 'CoercionI', see also 'mkForAllCoercion' mkForAllTyCoI :: TyVar -> CoercionI -> CoercionI mkForAllTyCoI _ IdCo = IdCo mkForAllTyCoI tv (ACo co) = ACo $ ForAllTy tv co +-- | Extract a 'Coercion' from a 'CoercionI' if it represents one. If it is the identity coercion, +-- panic fromACo :: CoercionI -> Coercion fromACo (ACo co) = co +-- | Smart constructor for class 'Coercion's on 'CoercionI'. Satisfies: +-- +-- > mkClassPPredCoI cls tys cois :: PredTy (cls tys) ~ PredTy (cls (tys `cast` cois)) mkClassPPredCoI :: Class -> [Type] -> [CoercionI] -> CoercionI --- 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) + | allIdCoIs cois = IdCo + | otherwise = ACo $ PredTy $ ClassP cls (zipCoArgs cois tys) +-- | Smart constructor for implicit parameter 'Coercion's on 'CoercionI'. Similar to 'mkClassPPredCoI' mkIParamPredCoI :: (IPName Name) -> CoercionI -> CoercionI --- Similar invariant to mkclassPPredCoI mkIParamPredCoI _ IdCo = IdCo mkIParamPredCoI ipn (ACo co) = ACo $ PredTy $ IParam ipn co +-- | Smart constructor for type equality 'Coercion's on 'CoercionI'. Similar to 'mkClassPPredCoI' 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 _ (ACo co1) ty2 coi2 = ACo $ PredTy $ EqPred co1 (fromCoI coi2 ty2) \end{code} +%************************************************************************ +%* * + Optimising coercions +%* * +%************************************************************************ + +\begin{code} +optCoercion :: Coercion -> Coercion +optCoercion co + = ASSERT2( coercionKind co `eq` coercionKind result, + ppr co $$ ppr result $$ ppr (coercionKind co) $$ ppr (coercionKind result) ) + result + where + (s1,t1) `eq` (s2,t2) = s1 `coreEqType` s2 && t1 `coreEqType` t2 + + (result,_,_) = go co + -- optimized, changed?, identity? + go :: Coercion -> ( Coercion, Bool, Bool ) + -- traverse coercion term bottom up and return + -- + -- 1) equivalent coercion, in optimized form + -- + -- 2) whether the output coercion differs from + -- the input coercion + -- + -- 3) whether the coercion is an identity coercion + -- + -- Performs the following optimizations: + -- + -- sym id >-> id + -- trans id co >-> co + -- trans co id >-> co + -- + go ty@(TyVarTy a) | isCoVar a = let (ty1,ty2) = coercionKind ty + in (ty, False, ty1 `coreEqType` ty2) + | otherwise = (ty, False, True) + go ty@(AppTy ty1 ty2) + = let (ty1', chan1, id1) = go ty1 + (ty2', chan2, id2) = go ty2 + in if chan1 || chan2 + then (AppTy ty1' ty2', True, id1 && id2) + else (ty , False, id1 && id2) + go ty@(TyConApp tc args) + | tc == symCoercionTyCon, [ty1] <- args + = case go ty1 of + (ty1', _ , True) -> (ty1', True, True) + (ty1', True, _ ) -> (TyConApp tc [ty1'], True, False) + (_ , _ , _ ) -> (ty, False, False) + | tc == transCoercionTyCon, [ty1,ty2] <- args + = let (ty1', chan1, id1) = go ty1 + (ty2', chan2, id2) = go ty2 + in if id1 + then (ty2', True, id2) + else if id2 + then (ty1', True, False) + else if chan1 || chan2 + then (TyConApp tc [ty1',ty2'], True , False) + else (ty , False, False) + | tc == leftCoercionTyCon, [ty1] <- args + = let (ty1', chan1, id1) = go ty1 + in if chan1 + then (TyConApp tc [ty1'], True , id1) + else (ty , False, id1) + | tc == rightCoercionTyCon, [ty1] <- args + = let (ty1', chan1, id1) = go ty1 + in if chan1 + then (TyConApp tc [ty1'], True , id1) + else (ty , False, id1) + | not (isCoercionTyCon tc) + = let (args', chans, ids) = mapAndUnzip3 go args + in if or chans + then (TyConApp tc args', True , and ids) + else (ty , False, and ids) + | otherwise + = (ty, False, False) + go ty@(FunTy ty1 ty2) + = let (ty1',chan1,id1) = go ty1 + (ty2',chan2,id2) = go ty2 + in if chan1 || chan2 + then (FunTy ty1' ty2', True , id1 && id2) + else (ty , False, id1 && id2) + go ty@(ForAllTy tv ty1) + = let (ty1', chan1, id1) = go ty1 + in if chan1 + then (ForAllTy tv ty1', True , id1) + else (ty , False, id1) + go ty@(PredTy (EqPred ty1 ty2)) + = let (ty1', chan1, id1) = go ty1 + (ty2', chan2, id2) = go ty2 + in if chan1 || chan2 + then (PredTy (EqPred ty1' ty2'), True , id1 && id2) + else (ty , False, id1 && id2) + go ty@(PredTy (ClassP cl args)) + = let (args', chans, ids) = mapAndUnzip3 go args + in if or chans + then (PredTy (ClassP cl args'), True , and ids) + else (ty , False, and ids) + go ty@(PredTy (IParam name ty1)) + = let (ty1', chan1, id1) = go ty1 + in if chan1 + then (PredTy (IParam name ty1'), True , id1) + else (ty , False, id1) +\end{code}