Data/Typeable/Internal.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE CPP #-}
    {-# LANGUAGE ConstraintKinds #-}
    {-# LANGUAGE DataKinds #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE MagicHash #-}
    {-# LANGUAGE NoImplicitPrelude #-}
    {-# LANGUAGE PolyKinds #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE UndecidableInstances #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Typeable.Internal
    -- Copyright   :  (c) The University of Glasgow, CWI 2001--2011
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- The representations of the types TyCon and TypeRep, and the
    -- function mkTyCon which is used by derived instances of Typeable to
    -- construct a TyCon.
    --
    -----------------------------------------------------------------------------

    module Data.Typeable.Internal (
        Proxy (..),
        TypeRep(..),
        KindRep,
        Fingerprint(..),
        typeOf, typeOf1, typeOf2, typeOf3, typeOf4, typeOf5, typeOf6, typeOf7,
        Typeable1, Typeable2, Typeable3, Typeable4, Typeable5, Typeable6, Typeable7,
        TyCon(..),
        typeRep,
        mkTyCon,
        mkTyCon3,
        mkTyConApp,
        mkPolyTyConApp,
        mkAppTy,
        typeRepTyCon,
        Typeable(..),
        mkFunTy,
        splitTyConApp,
        splitPolyTyConApp,
        funResultTy,
        typeRepArgs,
        typeRepFingerprint,
        rnfTypeRep,
        showsTypeRep,
        tyConString,
        rnfTyCon,
        listTc, funTc,
        typeRepKinds,
        typeLitTypeRep
      ) where

    import GHC.Base
    import GHC.Word
    import GHC.Show
    import Data.Proxy

    import GHC.Fingerprint.Type
    import {-# SOURCE #-} GHC.Fingerprint
       -- loop: GHC.Fingerprint -> Foreign.Ptr -> Data.Typeable
       -- Better to break the loop here, because we want non-SOURCE imports
       -- of Data.Typeable as much as possible so we can optimise the derived
       -- instances.

    -- | A concrete representation of a (monomorphic) type.  'TypeRep'
    -- supports reasonably efficient equality.
    data TypeRep = TypeRep {-# UNPACK #-} !Fingerprint TyCon [KindRep] [TypeRep]

    type KindRep = TypeRep

    -- Compare keys for equality
    instance Eq TypeRep where
      TypeRep x _ _ _ == TypeRep y _ _ _ = x == y

    instance Ord TypeRep where
      TypeRep x _ _ _ <= TypeRep y _ _ _ = x <= y

    -- | An abstract representation of a type constructor.  'TyCon' objects can
    -- be built using 'mkTyCon'.
    data TyCon = TyCon {
       tyConFingerprint :: {-# UNPACK #-} !Fingerprint, -- ^ @since 4.8.0.0
       tyConPackage :: String, -- ^ @since 4.5.0.0
       tyConModule  :: String, -- ^ @since 4.5.0.0
       tyConName    :: String  -- ^ @since 4.5.0.0
     }

    instance Eq TyCon where
      (TyCon t1 _ _ _) == (TyCon t2 _ _ _) = t1 == t2

    instance Ord TyCon where
      (TyCon k1 _ _ _) <= (TyCon k2 _ _ _) = k1 <= k2

    ----------------- Construction --------------------

    #include "MachDeps.h"

    -- mkTyCon is an internal function to make it easier for GHC to
    -- generate derived instances.  GHC precomputes the MD5 hash for the
    -- TyCon and passes it as two separate 64-bit values to mkTyCon.  The
    -- TyCon for a derived Typeable instance will end up being statically
    -- allocated.

    #if WORD_SIZE_IN_BITS < 64
    mkTyCon :: Word64# -> Word64# -> String -> String -> String -> TyCon
    #else
    mkTyCon :: Word#   -> Word#   -> String -> String -> String -> TyCon
    #endif
    mkTyCon high# low# pkg modl name
      = TyCon (Fingerprint (W64# high#) (W64# low#)) pkg modl name

    -- | Applies a polymorhic type constructor to a sequence of kinds and types
    mkPolyTyConApp :: TyCon -> [KindRep] -> [TypeRep] -> TypeRep
    mkPolyTyConApp tc@(TyCon tc_k _ _ _) [] [] = TypeRep tc_k tc [] []
    mkPolyTyConApp tc@(TyCon tc_k _ _ _) kinds types =
      TypeRep (fingerprintFingerprints (tc_k : arg_ks)) tc kinds types
      where
      arg_ks = [ k | TypeRep k _ _ _ <- kinds ++ types ]

    -- | Applies a monomorphic type constructor to a sequence of types
    mkTyConApp  :: TyCon -> [TypeRep] -> TypeRep
    mkTyConApp tc = mkPolyTyConApp tc []

    -- | A special case of 'mkTyConApp', which applies the function
    -- type constructor to a pair of types.
    mkFunTy  :: TypeRep -> TypeRep -> TypeRep
    mkFunTy f a = mkTyConApp funTc [f,a]

    -- | Splits a type constructor application.
    -- Note that if the type construcotr is polymorphic, this will
    -- not return the kinds that were used.
    -- See 'splitPolyTyConApp' if you need all parts.
    splitTyConApp :: TypeRep -> (TyCon,[TypeRep])
    splitTyConApp (TypeRep _ tc _ trs) = (tc,trs)

    -- | Split a type constructor application
    splitPolyTyConApp :: TypeRep -> (TyCon,[KindRep],[TypeRep])
    splitPolyTyConApp (TypeRep _ tc ks trs) = (tc,ks,trs)

    -- | Applies a type to a function type.  Returns: @'Just' u@ if the
    -- first argument represents a function of type @t -> u@ and the
    -- second argument represents a function of type @t@.  Otherwise,
    -- returns 'Nothing'.
    funResultTy :: TypeRep -> TypeRep -> Maybe TypeRep
    funResultTy trFun trArg
      = case splitTyConApp trFun of
          (tc, [t1,t2]) | tc == funTc && t1 == trArg -> Just t2
          _ -> Nothing

    -- | Adds a TypeRep argument to a TypeRep.
    mkAppTy :: TypeRep -> TypeRep -> TypeRep
    mkAppTy (TypeRep _ tc ks trs) arg_tr = mkPolyTyConApp tc ks (trs ++ [arg_tr])
       -- Notice that we call mkTyConApp to construct the fingerprint from tc and
       -- the arg fingerprints.  Simply combining the current fingerprint with
       -- the new one won't give the same answer, but of course we want to
       -- ensure that a TypeRep of the same shape has the same fingerprint!
       -- See Trac #5962

    -- | Builds a 'TyCon' object representing a type constructor.  An
    -- implementation of "Data.Typeable" should ensure that the following holds:
    --
    -- >  A==A' ^ B==B' ^ C==C' ==> mkTyCon A B C == mkTyCon A' B' C'
    --

    --
    mkTyCon3 :: String       -- ^ package name
             -> String       -- ^ module name
             -> String       -- ^ the name of the type constructor
             -> TyCon        -- ^ A unique 'TyCon' object
    mkTyCon3 pkg modl name =
      TyCon (fingerprintString (pkg ++ (' ':modl) ++ (' ':name))) pkg modl name

    ----------------- Observation ---------------------

    -- | Observe the type constructor of a type representation
    typeRepTyCon :: TypeRep -> TyCon
    typeRepTyCon (TypeRep _ tc _ _) = tc

    -- | Observe the argument types of a type representation
    typeRepArgs :: TypeRep -> [TypeRep]
    typeRepArgs (TypeRep _ _ _ tys) = tys

    -- | Observe the argument kinds of a type representation
    typeRepKinds :: TypeRep -> [KindRep]
    typeRepKinds (TypeRep _ _ ks _) = ks

    -- | Observe string encoding of a type representation
    {-# DEPRECATED tyConString "renamed to 'tyConName'; 'tyConModule' and 'tyConPackage' are also available." #-} -- deprecated in 7.4
    tyConString :: TyCon   -> String
    tyConString = tyConName

    -- | Observe the 'Fingerprint' of a type representation
    --
    -- @since 4.8.0.0
    typeRepFingerprint :: TypeRep -> Fingerprint
    typeRepFingerprint (TypeRep fpr _ _ _) = fpr

    -------------------------------------------------------------
    --
    --      The Typeable class and friends
    --
    -------------------------------------------------------------

    -- | The class 'Typeable' allows a concrete representation of a type to
    -- be calculated.
    class Typeable a where
      typeRep# :: Proxy# a -> TypeRep

    -- | Takes a value of type @a@ and returns a concrete representation
    -- of that type.
    --
    -- @since 4.7.0.0
    typeRep :: forall proxy a. Typeable a => proxy a -> TypeRep
    typeRep _ = typeRep# (proxy# :: Proxy# a)
    {-# INLINE typeRep #-}

    -- Keeping backwards-compatibility
    typeOf :: forall a. Typeable a => a -> TypeRep
    typeOf _ = typeRep (Proxy :: Proxy a)

    typeOf1 :: forall t (a :: *). Typeable t => t a -> TypeRep
    typeOf1 _ = typeRep (Proxy :: Proxy t)

    typeOf2 :: forall t (a :: *) (b :: *). Typeable t => t a b -> TypeRep
    typeOf2 _ = typeRep (Proxy :: Proxy t)

    typeOf3 :: forall t (a :: *) (b :: *) (c :: *). Typeable t
            => t a b c -> TypeRep
    typeOf3 _ = typeRep (Proxy :: Proxy t)

    typeOf4 :: forall t (a :: *) (b :: *) (c :: *) (d :: *). Typeable t
            => t a b c d -> TypeRep
    typeOf4 _ = typeRep (Proxy :: Proxy t)

    typeOf5 :: forall t (a :: *) (b :: *) (c :: *) (d :: *) (e :: *). Typeable t
            => t a b c d e -> TypeRep
    typeOf5 _ = typeRep (Proxy :: Proxy t)

    typeOf6 :: forall t (a :: *) (b :: *) (c :: *) (d :: *) (e :: *) (f :: *).
                    Typeable t => t a b c d e f -> TypeRep
    typeOf6 _ = typeRep (Proxy :: Proxy t)

    typeOf7 :: forall t (a :: *) (b :: *) (c :: *) (d :: *) (e :: *) (f :: *)
                    (g :: *). Typeable t => t a b c d e f g -> TypeRep
    typeOf7 _ = typeRep (Proxy :: Proxy t)

    type Typeable1 (a :: * -> *)                               = Typeable a
    type Typeable2 (a :: * -> * -> *)                          = Typeable a
    type Typeable3 (a :: * -> * -> * -> *)                     = Typeable a
    type Typeable4 (a :: * -> * -> * -> * -> *)                = Typeable a
    type Typeable5 (a :: * -> * -> * -> * -> * -> *)           = Typeable a
    type Typeable6 (a :: * -> * -> * -> * -> * -> * -> *)      = Typeable a
    type Typeable7 (a :: * -> * -> * -> * -> * -> * -> * -> *) = Typeable a

    {-# DEPRECATED Typeable1 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable2 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable3 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable4 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable5 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable6 "renamed to 'Typeable'" #-} -- deprecated in 7.8
    {-# DEPRECATED Typeable7 "renamed to 'Typeable'" #-} -- deprecated in 7.8

    ----------------- Showing TypeReps --------------------

    instance Show TypeRep where
      showsPrec p (TypeRep _ tycon kinds tys) =
        case tys of
          [] -> showsPrec p tycon
          [x]   | tycon == listTc -> showChar '[' . shows x . showChar ']'
          [a,r] | tycon == funTc  -> showParen (p > 8) $
                                     showsPrec 9 a .
                                     showString " -> " .
                                     showsPrec 8 r
          xs | isTupleTyCon tycon -> showTuple xs
             | otherwise         ->
                showParen (p > 9) $
                showsPrec p tycon .
                showChar ' '      .
                showArgs (showChar ' ') (kinds ++ tys)

    showsTypeRep :: TypeRep -> ShowS
    showsTypeRep = shows

    instance Show TyCon where
      showsPrec _ t = showString (tyConName t)

    isTupleTyCon :: TyCon -> Bool
    isTupleTyCon (TyCon _ _ _ ('(':',':_)) = True
    isTupleTyCon _                         = False

    -- | Helper to fully evaluate 'TypeRep' for use as @NFData(rnf)@ implementation
    --
    -- @since 4.8.0.0
    rnfTypeRep :: TypeRep -> ()
    rnfTypeRep (TypeRep _ tyc krs tyrs) = rnfTyCon tyc `seq` go krs `seq` go tyrs
      where
        go [] = ()
        go (x:xs) = rnfTypeRep x `seq` go xs

    -- | Helper to fully evaluate 'TyCon' for use as @NFData(rnf)@ implementation
    --
    -- @since 4.8.0.0
    rnfTyCon :: TyCon -> ()
    rnfTyCon (TyCon _ tcp tcm tcn) = go tcp `seq` go tcm `seq` go tcn
      where
        go [] = ()
        go (x:xs) = x `seq` go xs

    -- Some (Show.TypeRep) helpers:

    showArgs :: Show a => ShowS -> [a] -> ShowS
    showArgs _   []     = id
    showArgs _   [a]    = showsPrec 10 a
    showArgs sep (a:as) = showsPrec 10 a . sep . showArgs sep as

    showTuple :: [TypeRep] -> ShowS
    showTuple args = showChar '('
                   . showArgs (showChar ',') args
                   . showChar ')'

    listTc :: TyCon
    listTc = typeRepTyCon (typeOf [()])

    funTc :: TyCon
    funTc = typeRepTyCon (typeRep (Proxy :: Proxy (->)))

    -- | An internal function, to make representations for type literals.
    typeLitTypeRep :: String -> TypeRep
    typeLitTypeRep nm = rep
        where
        rep = mkTyConApp tc []
        tc = TyCon
               { tyConFingerprint = fingerprintString (mk pack modu nm)
               , tyConPackage  = pack
               , tyConModule   = modu
               , tyConName     = nm
               }
        pack = "base"
        modu = "GHC.TypeLits"
        mk a b c = a ++ " " ++ b ++ " " ++ c