{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1998 \section[PatSyn]{@PatSyn@: Pattern synonyms} -} {-# LANGUAGE CPP, DeriveDataTypeable #-} module PatSyn ( -- * Main data types PatSyn, mkPatSyn, -- ** Type deconstruction patSynName, patSynArity, patSynIsInfix, patSynArgs, patSynTyDetails, patSynType, patSynMatcher, patSynBuilder, patSynExTyVars, patSynSig, patSynInstArgTys, patSynInstResTy, tidyPatSynIds ) where #include "HsVersions.h" import Type import TcType( mkSigmaTy ) import Name import Outputable import Unique import Util import BasicTypes import FastString import Var import HsBinds( HsPatSynDetails(..) ) import qualified Data.Data as Data import qualified Data.Typeable import Data.Function {- ************************************************************************ * * \subsection{Pattern synonyms} * * ************************************************************************ -} -- | A pattern synonym -- See Note [Pattern synonym representation] data PatSyn = MkPatSyn { psName :: Name, psUnique :: Unique, -- Cached from Name psArgs :: [Type], psArity :: Arity, -- == length psArgs psInfix :: Bool, -- True <=> declared infix psUnivTyVars :: [TyVar], -- Universially-quantified type variables psReqTheta :: ThetaType, -- Required dictionaries psExTyVars :: [TyVar], -- Existentially-quantified type vars psProvTheta :: ThetaType, -- Provided dictionaries psOrigResTy :: Type, -- Mentions only psUnivTyVars -- See Note [Matchers and builders for pattern synonyms] psMatcher :: (Id, Bool), -- Matcher function. -- If Bool is True then prov_theta and arg_tys are empty -- and type is -- forall (r :: ?) univ_tvs. req_theta -- => res_ty -- -> (forall ex_tvs. Void# -> r) -- -> (Void# -> r) -- -> r -- -- Otherwise type is -- forall (r :: ?) univ_tvs. req_theta -- => res_ty -- -> (forall ex_tvs. prov_theta => arg_tys -> r) -- -> (Void# -> r) -- -> r psBuilder :: Maybe (Id, Bool) -- Nothing => uni-directional pattern synonym -- Just (builder, is_unlifted) => bi-directional -- Builder function, of type -- forall univ_tvs, ex_tvs. (prov_theta, req_theta) -- => arg_tys -> res_ty -- See Note [Builder for pattern synonyms with unboxed type] } deriving Data.Typeable.Typeable {- Note [Pattern synonym representation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the following pattern synonym declaration pattern P x = MkT [x] (Just 42) where data T a where MkT :: (Show a, Ord b) => [b] -> a -> T a so pattern P has type b -> T (Maybe t) with the following typeclass constraints: provides: (Show (Maybe t), Ord b) requires: (Eq t, Num t) In this case, the fields of MkPatSyn will be set as follows: psArgs = [b] psArity = 1 psInfix = False psUnivTyVars = [t] psExTyVars = [b] psProvTheta = (Show (Maybe t), Ord b) psReqTheta = (Eq t, Num t) psOrigResTy = T (Maybe t) Note [Matchers and builders for pattern synonyms] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For each pattern synonym P, we generate * a "matcher" function, used to desugar uses of P in patterns, which implements pattern matching * A "builder" function (for bidirectional pattern synonyms only), used to desugar uses of P in expressions, which constructs P-values. For the above example, the matcher function has type: $mP :: forall (r :: ?) t. (Eq t, Num t) => T (Maybe t) -> (forall b. (Show (Maybe t), Ord b) => b -> r) -> (Void# -> r) -> r with the following implementation: $mP @r @t $dEq $dNum scrut cont fail = case scrut of MkT @b $dShow $dOrd [x] (Just 42) -> cont @b $dShow $dOrd x _ -> fail Void# Notice that the return type 'r' has an open kind, so that it can be instantiated by an unboxed type; for example where we see f (P x) = 3# The extra Void# argument for the failure continuation is needed so that it is lazy even when the result type is unboxed. For the same reason, if the pattern has no arguments, an extra Void# argument is added to the success continuation as well. For *bidirectional* pattern synonyms, we also generate a "builder" function which implements the pattern synonym in an expression context. For our running example, it will be: $bP :: forall t b. (Show (Maybe t), Ord b, Eq t, Num t) => b -> T (Maybe t) $bP x = MkT [x] (Just 42) NB: the existential/universal and required/provided split does not apply to the builder since you are only putting stuff in, not getting stuff out. Injectivity of bidirectional pattern synonyms is checked in tcPatToExpr which walks the pattern and returns its corresponding expression when available. Note [Builder for pattern synonyms with unboxed type] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For bidirectional pattern synonyms that have no arguments and have an unboxed type, we add an extra Void# argument to the builder, else it would be a top-level declaration with an unboxed type. pattern P = 0# $bP :: Void# -> Int# $bP _ = 0# This means that when typechecking an occurrence of P in an expression, we must remember that the builder has this void argument. This is done by TcPatSyn.patSynBuilderOcc. ************************************************************************ * * \subsection{Instances} * * ************************************************************************ -} instance Eq PatSyn where (==) = (==) `on` getUnique (/=) = (/=) `on` getUnique instance Ord PatSyn where (<=) = (<=) `on` getUnique (<) = (<) `on` getUnique (>=) = (>=) `on` getUnique (>) = (>) `on` getUnique compare = compare `on` getUnique instance Uniquable PatSyn where getUnique = psUnique instance NamedThing PatSyn where getName = patSynName instance Outputable PatSyn where ppr = ppr . getName instance OutputableBndr PatSyn where pprInfixOcc = pprInfixName . getName pprPrefixOcc = pprPrefixName . getName instance Data.Data PatSyn where -- don't traverse? toConstr _ = abstractConstr "PatSyn" gunfold _ _ = error "gunfold" dataTypeOf _ = mkNoRepType "PatSyn" {- ************************************************************************ * * \subsection{Construction} * * ************************************************************************ -} -- | Build a new pattern synonym mkPatSyn :: Name -> Bool -- ^ Is the pattern synonym declared infix? -> ([TyVar], ThetaType) -- ^ Universially-quantified type variables -- and required dicts -> ([TyVar], ThetaType) -- ^ Existentially-quantified type variables -- and provided dicts -> [Type] -- ^ Original arguments -> Type -- ^ Original result type -> (Id, Bool) -- ^ Name of matcher -> Maybe (Id, Bool) -- ^ Name of builder -> PatSyn mkPatSyn name declared_infix (univ_tvs, req_theta) (ex_tvs, prov_theta) orig_args orig_res_ty matcher builder = MkPatSyn {psName = name, psUnique = getUnique name, psUnivTyVars = univ_tvs, psExTyVars = ex_tvs, psProvTheta = prov_theta, psReqTheta = req_theta, psInfix = declared_infix, psArgs = orig_args, psArity = length orig_args, psOrigResTy = orig_res_ty, psMatcher = matcher, psBuilder = builder } -- | The 'Name' of the 'PatSyn', giving it a unique, rooted identification patSynName :: PatSyn -> Name patSynName = psName patSynType :: PatSyn -> Type -- The full pattern type, used only in error messages patSynType (MkPatSyn { psUnivTyVars = univ_tvs, psReqTheta = req_theta , psExTyVars = ex_tvs, psProvTheta = prov_theta , psArgs = orig_args, psOrigResTy = orig_res_ty }) = mkSigmaTy univ_tvs req_theta $ mkSigmaTy ex_tvs prov_theta $ mkFunTys orig_args orig_res_ty -- | Should the 'PatSyn' be presented infix? patSynIsInfix :: PatSyn -> Bool patSynIsInfix = psInfix -- | Arity of the pattern synonym patSynArity :: PatSyn -> Arity patSynArity = psArity patSynArgs :: PatSyn -> [Type] patSynArgs = psArgs patSynTyDetails :: PatSyn -> HsPatSynDetails Type patSynTyDetails (MkPatSyn { psInfix = is_infix, psArgs = arg_tys }) | is_infix, [left,right] <- arg_tys = InfixPatSyn left right | otherwise = PrefixPatSyn arg_tys patSynExTyVars :: PatSyn -> [TyVar] patSynExTyVars = psExTyVars patSynSig :: PatSyn -> ([TyVar], [TyVar], ThetaType, ThetaType, [Type], Type) patSynSig (MkPatSyn { psUnivTyVars = univ_tvs, psExTyVars = ex_tvs , psProvTheta = prov, psReqTheta = req , psArgs = arg_tys, psOrigResTy = res_ty }) = (univ_tvs, ex_tvs, prov, req, arg_tys, res_ty) patSynMatcher :: PatSyn -> (Id,Bool) patSynMatcher = psMatcher patSynBuilder :: PatSyn -> Maybe (Id, Bool) patSynBuilder = psBuilder tidyPatSynIds :: (Id -> Id) -> PatSyn -> PatSyn tidyPatSynIds tidy_fn ps@(MkPatSyn { psMatcher = matcher, psBuilder = builder }) = ps { psMatcher = tidy_pr matcher, psBuilder = fmap tidy_pr builder } where tidy_pr (id, dummy) = (tidy_fn id, dummy) patSynInstArgTys :: PatSyn -> [Type] -> [Type] -- Return the types of the argument patterns -- e.g. data D a = forall b. MkD a b (b->a) -- pattern P f x y = MkD (x,True) y f -- D :: forall a. forall b. a -> b -> (b->a) -> D a -- P :: forall c. forall b. (b->(c,Bool)) -> c -> b -> P c -- patSynInstArgTys P [Int,bb] = [bb->(Int,Bool), Int, bb] -- NB: the inst_tys should be both universal and existential patSynInstArgTys (MkPatSyn { psName = name, psUnivTyVars = univ_tvs , psExTyVars = ex_tvs, psArgs = arg_tys }) inst_tys = ASSERT2( length tyvars == length inst_tys , ptext (sLit "patSynInstArgTys") <+> ppr name $$ ppr tyvars $$ ppr inst_tys ) map (substTyWith tyvars inst_tys) arg_tys where tyvars = univ_tvs ++ ex_tvs patSynInstResTy :: PatSyn -> [Type] -> Type -- Return the type of whole pattern -- E.g. pattern P x y = Just (x,x,y) -- P :: a -> b -> Just (a,a,b) -- (patSynInstResTy P [Int,Bool] = Maybe (Int,Int,Bool) -- NB: unlikepatSynInstArgTys, the inst_tys should be just the *universal* tyvars patSynInstResTy (MkPatSyn { psName = name, psUnivTyVars = univ_tvs , psOrigResTy = res_ty }) inst_tys = ASSERT2( length univ_tvs == length inst_tys , ptext (sLit "patSynInstResTy") <+> ppr name $$ ppr univ_tvs $$ ppr inst_tys ) substTyWith univ_tvs inst_tys res_ty