{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE TypeInType #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE TypeApplications #-}

-----------------------------------------------------------------------------
-- |
-- 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 (
    -- * Typeable and kind polymorphism
    --
    -- #kind_instantiation

    -- * Miscellaneous
    Fingerprint(..),

    -- * Typeable class
    Typeable(..),
    withTypeable,

    -- * Module
    Module,  -- Abstract
    moduleName, modulePackage, rnfModule,

    -- * TyCon
    TyCon,   -- Abstract
    tyConPackage, tyConModule, tyConName, tyConKindArgs, tyConKindRep,
    tyConFingerprint,
    KindRep(.., KindRepTypeLit), TypeLitSort(..),
    rnfTyCon,

    -- * TypeRep
    TypeRep,
    pattern App, pattern Con, pattern Con', pattern Fun,
    typeRep,
    typeOf,
    typeRepTyCon,
    typeRepFingerprint,
    rnfTypeRep,
    eqTypeRep,
    typeRepKind,
    splitApps,

    -- * SomeTypeRep
    SomeTypeRep(..),
    someTypeRep,
    someTypeRepTyCon,
    someTypeRepFingerprint,
    rnfSomeTypeRep,

    -- * Construction
    -- | These are for internal use only
    mkTrCon, mkTrApp, mkTrFun,
    mkTyCon, mkTyCon#,
    typeSymbolTypeRep, typeNatTypeRep,
  ) where

import GHC.Base
import qualified GHC.Arr as A
import GHC.Types ( TYPE )
import Data.Type.Equality
import GHC.List ( splitAt, foldl' )
import GHC.Word
import GHC.Show
import GHC.TypeLits ( KnownSymbol, symbolVal' )
import GHC.TypeNats ( KnownNat, natVal' )
import Unsafe.Coerce ( unsafeCoerce )

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.

#include "MachDeps.h"

{- *********************************************************************
*                                                                      *
                The TyCon type
*                                                                      *
********************************************************************* -}

modulePackage :: Module -> String
modulePackage (Module p _) = trNameString p

moduleName :: Module -> String
moduleName (Module _ m) = trNameString m

tyConPackage :: TyCon -> String
tyConPackage (TyCon _ _ m _ _ _) = modulePackage m

tyConModule :: TyCon -> String
tyConModule (TyCon _ _ m _ _ _) = moduleName m

tyConName :: TyCon -> String
tyConName (TyCon _ _ _ n _ _) = trNameString n

trNameString :: TrName -> String
trNameString (TrNameS s) = unpackCStringUtf8# s
trNameString (TrNameD s) = s

tyConFingerprint :: TyCon -> Fingerprint
tyConFingerprint (TyCon hi lo _ _ _ _)
  = Fingerprint (W64# hi) (W64# lo)

tyConKindArgs :: TyCon -> Int
tyConKindArgs (TyCon _ _ _ _ n _) = I# n

tyConKindRep :: TyCon -> KindRep
tyConKindRep (TyCon _ _ _ _ _ k) = k

-- | Helper to fully evaluate 'TyCon' for use as @NFData(rnf)@ implementation
--
-- @since 4.8.0.0
rnfModule :: Module -> ()
rnfModule (Module p m) = rnfTrName p `seq` rnfTrName m

rnfTrName :: TrName -> ()
rnfTrName (TrNameS _) = ()
rnfTrName (TrNameD n) = rnfString n

rnfKindRep :: KindRep -> ()
rnfKindRep (KindRepTyConApp tc args) = rnfTyCon tc `seq` rnfList rnfKindRep args
rnfKindRep (KindRepVar _)   = ()
rnfKindRep (KindRepApp a b) = rnfKindRep a `seq` rnfKindRep b
rnfKindRep (KindRepFun a b) = rnfKindRep a `seq` rnfKindRep b
rnfKindRep (KindRepTYPE rr) = rnfRuntimeRep rr
rnfKindRep (KindRepTypeLitS _ _) = ()
rnfKindRep (KindRepTypeLitD _ t) = rnfString t

rnfRuntimeRep :: RuntimeRep -> ()
rnfRuntimeRep (VecRep !_ !_) = ()
rnfRuntimeRep !_             = ()

rnfList :: (a -> ()) -> [a] -> ()
rnfList _     []     = ()
rnfList force (x:xs) = force x `seq` rnfList force xs

rnfString :: [Char] -> ()
rnfString = rnfList (`seq` ())

rnfTyCon :: TyCon -> ()
rnfTyCon (TyCon _ _ m n _ k) = rnfModule m `seq` rnfTrName n `seq` rnfKindRep k


{- *********************************************************************
*                                                                      *
                The TypeRep type
*                                                                      *
********************************************************************* -}

-- | A concrete representation of a (monomorphic) type.
-- 'TypeRep' supports reasonably efficient equality.
data TypeRep (a :: k) where
    TrTyCon :: {-# UNPACK #-} !Fingerprint -> !TyCon -> [SomeTypeRep]
            -> TypeRep (a :: k)
    TrApp   :: forall k1 k2 (a :: k1 -> k2) (b :: k1).
               {-# UNPACK #-} !Fingerprint
            -> TypeRep (a :: k1 -> k2)
            -> TypeRep (b :: k1)
            -> TypeRep (a b)
    TrFun   :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep)
                      (a :: TYPE r1) (b :: TYPE r2).
               {-# UNPACK #-} !Fingerprint
            -> TypeRep a
            -> TypeRep b
            -> TypeRep (a -> b)

-- Compare keys for equality

-- | @since 2.01
instance Eq (TypeRep a) where
  _ == _  = True
  {-# INLINABLE (==) #-}

instance TestEquality TypeRep where
  a `testEquality` b
    | Just HRefl <- eqTypeRep a b
    = Just Refl
    | otherwise
    = Nothing
  {-# INLINEABLE testEquality #-}

-- | @since 4.4.0.0
instance Ord (TypeRep a) where
  compare _ _ = EQ
  {-# INLINABLE compare #-}

-- | A non-indexed type representation.
data SomeTypeRep where
    SomeTypeRep :: forall k (a :: k). !(TypeRep a) -> SomeTypeRep

instance Eq SomeTypeRep where
  SomeTypeRep a == SomeTypeRep b =
      case a `eqTypeRep` b of
          Just _  -> True
          Nothing -> False

instance Ord SomeTypeRep where
  SomeTypeRep a `compare` SomeTypeRep b =
    typeRepFingerprint a `compare` typeRepFingerprint b

-- | The function type constructor.
--
-- For instance,
-- @
-- typeRep \@(Int -> Char) === Fun (typeRep \@Int) (typeRep \@Char)
-- @
--
pattern Fun :: forall k (fun :: k). ()
            => forall (r1 :: RuntimeRep) (r2 :: RuntimeRep)
                      (arg :: TYPE r1) (res :: TYPE r2).
               (k ~ Type, fun ~~ (arg -> res))
            => TypeRep arg
            -> TypeRep res
            -> TypeRep fun
pattern Fun arg res <- TrFun _ arg res
  where Fun arg res = mkTrFun arg res

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

-- | Construct a representation for a type constructor
-- applied at a monomorphic kind.
--
-- Note that this is unsafe as it allows you to construct
-- ill-kinded types.
mkTrCon :: forall k (a :: k). TyCon -> [SomeTypeRep] -> TypeRep a
mkTrCon tc kind_vars = TrTyCon fpr tc kind_vars
  where
    fpr_tc  = tyConFingerprint tc
    fpr_kvs = map someTypeRepFingerprint kind_vars
    fpr     = fingerprintFingerprints (fpr_tc:fpr_kvs)

-- | Construct a representation for a type application.
--
-- Note that this is known-key to the compiler, which uses it in desugar
-- 'Typeable' evidence.
mkTrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1).
           TypeRep (a :: k1 -> k2)
        -> TypeRep (b :: k1)
        -> TypeRep (a b)
mkTrApp a b = TrApp fpr a b
  where
    fpr_a = typeRepFingerprint a
    fpr_b = typeRepFingerprint b
    fpr   = fingerprintFingerprints [fpr_a, fpr_b]

-- | A type application.
--
-- For instance,
-- @
-- typeRep \@(Maybe Int) === App (typeRep \@Maybe) (typeRep \@Int)
-- @
-- Note that this will never match a function type (e.g. @Int -> [email protected]).
--
pattern App :: forall k2 (t :: k2). ()
            => forall k1 (a :: k1 -> k2) (b :: k1). (t ~ a b)
            => TypeRep a -> TypeRep b -> TypeRep t
pattern App f x <- TrApp _ f x
  where App f x = mkTrApp f x

-- | Use a 'TypeRep' as 'Typeable' evidence.
withTypeable :: forall a r. TypeRep a -> (Typeable a => r) -> r
withTypeable rep k = unsafeCoerce k' rep
  where k' :: Gift a r
        k' = Gift k

-- | A helper to satisfy the type checker in 'withTypeable'.
newtype Gift a r = Gift (Typeable a => r)

-- | Pattern match on a type constructor
pattern Con :: forall k (a :: k). TyCon -> TypeRep a
pattern Con con <- TrTyCon _ con _

-- | Pattern match on a type constructor including its instantiated kind
-- variables.
--
-- For instance,
-- @
-- App (Con' proxyTyCon ks) intRep = typeRep @(Proxy \@Int)
-- @
-- will bring into scope,
-- @
-- proxyTyCon :: TyCon
-- ks         == [someTypeRep @Type] :: [SomeTypeRep]
-- intRep     == typeRep @Int
-- @
--
pattern Con' :: forall k (a :: k). TyCon -> [SomeTypeRep] -> TypeRep a
pattern Con' con ks <- TrTyCon _ con ks

{-# COMPLETE Fun, App, Con  #-}
{-# COMPLETE Fun, App, Con' #-}

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

-- | Observe the type constructor of a quantified type representation.
someTypeRepTyCon :: SomeTypeRep -> TyCon
someTypeRepTyCon (SomeTypeRep t) = typeRepTyCon t

-- | Observe the type constructor of a type representation
typeRepTyCon :: TypeRep a -> TyCon
typeRepTyCon (TrTyCon _ tc _) = tc
typeRepTyCon (TrApp _ a _)    = typeRepTyCon a
typeRepTyCon (TrFun _ _ _)    = typeRepTyCon $ typeRep @(->)

-- | Type equality
--
-- @since 4.10
eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2).
             TypeRep a -> TypeRep b -> Maybe (a :~~: b)
eqTypeRep a b
  | typeRepFingerprint a == typeRepFingerprint b = Just (unsafeCoerce HRefl)
  | otherwise                                    = Nothing


-------------------------------------------------------------
--
--      Computing kinds
--
-------------------------------------------------------------

-- | Observe the kind of a type.
typeRepKind :: TypeRep (a :: k) -> TypeRep k
typeRepKind (TrTyCon _ tc args)
  = unsafeCoerceRep $ tyConKind tc args
typeRepKind (TrApp _ f _)
  | Fun _ res <- typeRepKind f
  = res
  | otherwise
  = error ("Ill-kinded type application: " ++ show (typeRepKind f))
typeRepKind (TrFun _ _ _) = typeRep @Type

tyConKind :: TyCon -> [SomeTypeRep] -> SomeTypeRep
tyConKind (TyCon _ _ _ _ nKindVars# kindRep) kindVars =
    let kindVarsArr :: A.Array KindBndr SomeTypeRep
        kindVarsArr = A.listArray (0, I# (nKindVars# -# 1#)) kindVars
    in instantiateKindRep kindVarsArr kindRep

instantiateKindRep :: A.Array KindBndr SomeTypeRep -> KindRep -> SomeTypeRep
instantiateKindRep vars = go
  where
    go :: KindRep -> SomeTypeRep
    go (KindRepTyConApp tc args)
      = let n_kind_args = tyConKindArgs tc
            (kind_args, ty_args) = splitAt n_kind_args args
            -- First instantiate tycon kind arguments
            tycon_app = SomeTypeRep $ mkTrCon tc (map go kind_args)
            -- Then apply remaining type arguments
            applyTy :: SomeTypeRep -> KindRep -> SomeTypeRep
            applyTy (SomeTypeRep acc) ty
              | SomeTypeRep ty' <- go ty
              = SomeTypeRep $ mkTrApp (unsafeCoerce acc) (unsafeCoerce ty')
        in foldl' applyTy tycon_app ty_args
    go (KindRepVar var)
      = vars A.! var
    go (KindRepApp f a)
      = SomeTypeRep $ App (unsafeCoerceRep $ go f) (unsafeCoerceRep $ go a)
    go (KindRepFun a b)
      = SomeTypeRep $ Fun (unsafeCoerceRep $ go a) (unsafeCoerceRep $ go b)
    go (KindRepTYPE r) = unkindedTypeRep $ tYPE `kApp` runtimeRepTypeRep r
    go (KindRepTypeLitS sort s)
      = mkTypeLitFromString sort (unpackCStringUtf8# s)
    go (KindRepTypeLitD sort s)
      = mkTypeLitFromString sort s

    tYPE = kindedTypeRep @(RuntimeRep -> Type) @TYPE

unsafeCoerceRep :: SomeTypeRep -> TypeRep a
unsafeCoerceRep (SomeTypeRep r) = unsafeCoerce r

unkindedTypeRep :: SomeKindedTypeRep k -> SomeTypeRep
unkindedTypeRep (SomeKindedTypeRep x) = SomeTypeRep x

data SomeKindedTypeRep k where
    SomeKindedTypeRep :: forall (a :: k). TypeRep a
                      -> SomeKindedTypeRep k

kApp :: SomeKindedTypeRep (k -> k')
     -> SomeKindedTypeRep k
     -> SomeKindedTypeRep k'
kApp (SomeKindedTypeRep f) (SomeKindedTypeRep a) =
    SomeKindedTypeRep (App f a)

kindedTypeRep :: forall (a :: k). Typeable a => SomeKindedTypeRep k
kindedTypeRep = SomeKindedTypeRep (typeRep @a)

buildList :: forall k. Typeable k
          => [SomeKindedTypeRep k]
          -> SomeKindedTypeRep [k]
buildList = foldr cons nil
  where
    nil = kindedTypeRep @[k] @'[]
    cons x rest = SomeKindedTypeRep (typeRep @'(:)) `kApp` x `kApp` rest

runtimeRepTypeRep :: RuntimeRep -> SomeKindedTypeRep RuntimeRep
runtimeRepTypeRep r =
    case r of
      LiftedRep   -> rep @'LiftedRep
      UnliftedRep -> rep @'UnliftedRep
      VecRep c e  -> kindedTypeRep @_ @'VecRep
                     `kApp` vecCountTypeRep c
                     `kApp` vecElemTypeRep e
      TupleRep rs -> kindedTypeRep @_ @'TupleRep
                     `kApp` buildList (map runtimeRepTypeRep rs)
      SumRep rs   -> kindedTypeRep @_ @'SumRep
                     `kApp` buildList (map runtimeRepTypeRep rs)
      IntRep      -> rep @'IntRep
      WordRep     -> rep @'WordRep
      Int64Rep    -> rep @'Int64Rep
      Word64Rep   -> rep @'Word64Rep
      AddrRep     -> rep @'AddrRep
      FloatRep    -> rep @'FloatRep
      DoubleRep   -> rep @'DoubleRep
  where
    rep :: forall (a :: RuntimeRep). Typeable a => SomeKindedTypeRep RuntimeRep
    rep = kindedTypeRep @RuntimeRep @a

vecCountTypeRep :: VecCount -> SomeKindedTypeRep VecCount
vecCountTypeRep c =
    case c of
      Vec2  -> rep @'Vec2
      Vec4  -> rep @'Vec4
      Vec8  -> rep @'Vec8
      Vec16 -> rep @'Vec16
      Vec32 -> rep @'Vec32
      Vec64 -> rep @'Vec64
  where
    rep :: forall (a :: VecCount). Typeable a => SomeKindedTypeRep VecCount
    rep = kindedTypeRep @VecCount @a

vecElemTypeRep :: VecElem -> SomeKindedTypeRep VecElem
vecElemTypeRep e =
    case e of
      Int8ElemRep     -> rep @'Int8ElemRep
      Int16ElemRep    -> rep @'Int16ElemRep
      Int32ElemRep    -> rep @'Int32ElemRep
      Int64ElemRep    -> rep @'Int64ElemRep
      Word8ElemRep    -> rep @'Word8ElemRep
      Word16ElemRep   -> rep @'Word16ElemRep
      Word32ElemRep   -> rep @'Word32ElemRep
      Word64ElemRep   -> rep @'Word64ElemRep
      FloatElemRep    -> rep @'FloatElemRep
      DoubleElemRep   -> rep @'DoubleElemRep
  where
    rep :: forall (a :: VecElem). Typeable a => SomeKindedTypeRep VecElem
    rep = kindedTypeRep @VecElem @a

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

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

typeRep :: Typeable a => TypeRep a
typeRep = typeRep#

typeOf :: Typeable a => a -> TypeRep a
typeOf _ = typeRep

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

someTypeRepFingerprint :: SomeTypeRep -> Fingerprint
someTypeRepFingerprint (SomeTypeRep t) = typeRepFingerprint t

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

-- This follows roughly the precedence structure described in Note [Precedence
-- in types].
instance Show (TypeRep (a :: k)) where
    showsPrec = showTypeable


showTypeable :: Int -> TypeRep (a :: k) -> ShowS
showTypeable _ rep
  | Just HRefl <- rep `eqTypeRep` (typeRep :: TypeRep Type) =
    showChar '*'
  | isListTyCon tc, [ty] <- tys =
    showChar '[' . shows ty . showChar ']'
  | isTupleTyCon tc =
    showChar '(' . showArgs (showChar ',') tys . showChar ')'
  where (tc, tys) = splitApps rep
showTypeable p (TrTyCon _ tycon [])
  = showsPrec p tycon
showTypeable p (TrTyCon _ tycon args)
  = showParen (p > 9) $
    showsPrec p tycon .
    showChar ' ' .
    showArgs (showChar ' ') args
showTypeable p (TrFun _ x r)
  = showParen (p > 8) $
    showsPrec 9 x . showString " -> " . showsPrec 8 r
showTypeable p (TrApp _ f x)
  = showParen (p > 9) $
    showsPrec 8 f .
    showChar ' ' .
    showsPrec 10 x

-- | @since 4.10.0.0
instance Show SomeTypeRep where
  showsPrec p (SomeTypeRep ty) = showsPrec p ty

splitApps :: TypeRep a -> (TyCon, [SomeTypeRep])
splitApps = go []
  where
    go :: [SomeTypeRep] -> TypeRep a -> (TyCon, [SomeTypeRep])
    go xs (TrTyCon _ tc _) = (tc, xs)
    go xs (TrApp _ f x)    = go (SomeTypeRep x : xs) f
    go [] (TrFun _ a b)    = (funTyCon, [SomeTypeRep a, SomeTypeRep b])
    go _  (TrFun _ _ _)    =
        errorWithoutStackTrace "Data.Typeable.Internal.splitApps: Impossible"

funTyCon :: TyCon
funTyCon = typeRepTyCon (typeRep @(->))

isListTyCon :: TyCon -> Bool
isListTyCon tc = tc == typeRepTyCon (typeRep :: TypeRep [Int])

isTupleTyCon :: TyCon -> Bool
isTupleTyCon tc
  | ('(':',':_) <- tyConName tc = True
  | otherwise                   = False

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

-- | Helper to fully evaluate 'TypeRep' for use as @NFData(rnf)@ implementation
--
-- @since 4.8.0.0
rnfTypeRep :: TypeRep a -> ()
rnfTypeRep (TrTyCon _ tyc _) = rnfTyCon tyc
rnfTypeRep (TrApp _ f x)     = rnfTypeRep f `seq` rnfTypeRep x
rnfTypeRep (TrFun _ x y)     = rnfTypeRep x `seq` rnfTypeRep y

-- | Helper to fully evaluate 'SomeTypeRep' for use as @NFData(rnf)@
-- implementation
--
-- @since 4.10.0.0
rnfSomeTypeRep :: SomeTypeRep -> ()
rnfSomeTypeRep (SomeTypeRep r) = rnfTypeRep r

{- *********************************************************
*                                                          *
*       TyCon/TypeRep definitions for type literals        *
*              (Symbol and Nat)                            *
*                                                          *
********************************************************* -}

pattern KindRepTypeLit :: TypeLitSort -> String -> KindRep
pattern KindRepTypeLit sort t <- (getKindRepTypeLit -> Just (sort, t))
  where
    KindRepTypeLit sort t = KindRepTypeLitD sort t

{-# COMPLETE KindRepTyConApp, KindRepVar, KindRepApp, KindRepFun,
             KindRepTYPE, KindRepTypeLit #-}

getKindRepTypeLit :: KindRep -> Maybe (TypeLitSort, String)
getKindRepTypeLit (KindRepTypeLitS sort t) = Just (sort, unpackCStringUtf8# t)
getKindRepTypeLit (KindRepTypeLitD sort t) = Just (sort, t)
getKindRepTypeLit _                        = Nothing

-- | Exquisitely unsafe.
mkTyCon# :: Addr#       -- ^ package name
         -> Addr#       -- ^ module name
         -> Addr#       -- ^ the name of the type constructor
         -> Int#        -- ^ number of kind variables
         -> KindRep     -- ^ kind representation
         -> TyCon       -- ^ A unique 'TyCon' object
mkTyCon# pkg modl name n_kinds kind_rep
  | Fingerprint (W64# hi) (W64# lo) <- fingerprint
  = TyCon hi lo mod (TrNameS name) n_kinds kind_rep
  where
    mod = Module (TrNameS pkg) (TrNameS modl)
    fingerprint :: Fingerprint
    fingerprint = mkTyConFingerprint (unpackCStringUtf8# pkg)
                                     (unpackCStringUtf8# modl)
                                     (unpackCStringUtf8# name)

-- it is extremely important that this fingerprint computation
-- remains in sync with that in TcTypeable to ensure that type
-- equality is correct.

-- | Exquisitely unsafe.
mkTyCon :: String       -- ^ package name
        -> String       -- ^ module name
        -> String       -- ^ the name of the type constructor
        -> Int         -- ^ number of kind variables
        -> KindRep     -- ^ kind representation
        -> TyCon        -- ^ A unique 'TyCon' object
-- Used when the strings are dynamically allocated,
-- eg from binary deserialisation
mkTyCon pkg modl name (I# n_kinds) kind_rep
  | Fingerprint (W64# hi) (W64# lo) <- fingerprint
  = TyCon hi lo mod (TrNameD name) n_kinds kind_rep
  where
    mod = Module (TrNameD pkg) (TrNameD modl)
    fingerprint :: Fingerprint
    fingerprint = mkTyConFingerprint pkg modl name

-- This must match the computation done in TcTypeable.mkTyConRepTyConRHS.
mkTyConFingerprint :: String -- ^ package name
                   -> String -- ^ module name
                   -> String -- ^ tycon name
                   -> Fingerprint
mkTyConFingerprint pkg_name mod_name tycon_name =
        fingerprintFingerprints
        [ fingerprintString pkg_name
        , fingerprintString mod_name
        , fingerprintString tycon_name
        ]

mkTypeLitTyCon :: String -> TyCon -> TyCon
mkTypeLitTyCon name kind_tycon
  = mkTyCon "base" "GHC.TypeLits" name 0 kind
  where kind = KindRepTyConApp kind_tycon []

-- | Used to make `'Typeable' instance for things of kind Nat
typeNatTypeRep :: KnownNat a => Proxy# a -> TypeRep a
typeNatTypeRep p = typeLitTypeRep (show (natVal' p)) tcNat

-- | Used to make `'Typeable' instance for things of kind Symbol
typeSymbolTypeRep :: KnownSymbol a => Proxy# a -> TypeRep a
typeSymbolTypeRep p = typeLitTypeRep (show (symbolVal' p)) tcSymbol

mkTypeLitFromString :: TypeLitSort -> String -> SomeTypeRep
mkTypeLitFromString TypeLitSymbol s =
    SomeTypeRep $ (typeLitTypeRep s tcSymbol :: TypeRep Symbol)
mkTypeLitFromString TypeLitNat s =
    SomeTypeRep $ (typeLitTypeRep s tcSymbol :: TypeRep Nat)

tcSymbol :: TyCon
tcSymbol = typeRepTyCon (typeRep @Symbol)

tcNat :: TyCon
tcNat = typeRepTyCon (typeRep @Nat)

-- | An internal function, to make representations for type literals.
typeLitTypeRep :: forall (a :: k). (Typeable k) => String -> TyCon -> TypeRep a
typeLitTypeRep nm kind_tycon = mkTrCon (mkTypeLitTyCon nm kind_tycon) []

-- | For compiler use.
mkTrFun :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep)
                  (a :: TYPE r1) (b :: TYPE r2).
           TypeRep a -> TypeRep b -> TypeRep ((a -> b) :: Type)
mkTrFun arg res = TrFun fpr arg res
  where fpr = fingerprintFingerprints [ typeRepFingerprint arg
                                      , typeRepFingerprint res]

{- $kind_instantiation

Consider a type like 'Data.Proxy.Proxy',

@
data Proxy :: forall k. k -> Type
@

One might think that one could decompose an instantiation of this type like
@Proxy [email protected] into two applications,

@
'App' (App a b) c === typeRep @(Proxy Int)
@

where,

@
a = typeRep @Proxy
b = typeRep @Type
c = typeRep @Int
@

However, this isn't the case. Instead we can only decompose into an application
and a constructor,

@
'App' ('Con' proxyTyCon) (typeRep @Int) === typeRep @(Proxy Int)
@

The reason for this is that 'Typeable' can only represent /kind-monomorphic/
types. That is, we must saturate enough of @[email protected]\'s arguments to
fully determine its kind. In the particular case of @[email protected] this means we must
instantiate the kind variable @[email protected] such that no @[email protected] variables
remain.

While it is not possible to decompose the 'Con' above into an application, it is
possible to observe the kind variable instantiations of the constructor with the
'Con\'' pattern,

@
'App' (Con' proxyTyCon kinds) _ === typeRep @(Proxy Int)
@

Here @[email protected] will be @[typeRep \@Type]@.

-}