{-# LANGUAGE Unsafe #-}
{-# LANGUAGE MagicHash, UnboxedTuples, DeriveDataTypeable, TypeFamilies, MultiParamTypeClasses, FlexibleInstances #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  GHC.Exts
-- Copyright   :  (c) The University of Glasgow 2002
-- License     :  see libraries/base/LICENSE
--
-- Maintainer  :  cvs-ghc@haskell.org
-- Stability   :  internal
-- Portability :  non-portable (GHC Extensions)
--
-- GHC Extensions: this is the Approved Way to get at GHC-specific extensions.
--
-- Note: no other base module should import this module.
-----------------------------------------------------------------------------

module GHC.Exts
       (
        -- * Representations of some basic types
        Int(..),Word(..),Float(..),Double(..),
        Char(..),
        Ptr(..), FunPtr(..),

        -- * The maximum tuple size
        maxTupleSize,

        -- * Primitive operations
        module GHC.Prim,
        shiftL#, shiftRL#, iShiftL#, iShiftRA#, iShiftRL#,
        uncheckedShiftL64#, uncheckedShiftRL64#,
        uncheckedIShiftL64#, uncheckedIShiftRA64#,
        isTrue#,

        -- * Fusion
        build, augment,

        -- * Overloaded string literals
        IsString(..),

        -- * Debugging
        breakpoint, breakpointCond,

        -- * Ids with special behaviour
        lazy, inline,

        -- * Safe coercions
        --
        -- | These are available from the /Trustworthy/ module "Data.Coerce" as well
        --
        -- /Since: 4.7.0.0/
        Data.Coerce.coerce, Data.Coerce.Coercible,

        -- * Transform comprehensions
        Down(..), groupWith, sortWith, the,

        -- * Event logging
        traceEvent,

        -- * SpecConstr annotations
        SpecConstrAnnotation(..),

        -- * The call stack
        currentCallStack,

        -- * The Constraint kind
        Constraint,

        -- * Overloaded lists
        IsList(..)
       ) where

import Prelude

import GHC.Prim hiding (coerce, Coercible)
import GHC.Base hiding (coerce, Coercible) -- implicitly comes from GHC.Prim
import GHC.Word
import GHC.Int
import GHC.Ptr
import GHC.Stack
import qualified Data.Coerce
import Data.String
import Data.List
import Data.Data
import Data.Ord
import qualified Debug.Trace
import GHC.Magic (inline)

-- XXX This should really be in Data.Tuple, where the definitions are
maxTupleSize :: Int
maxTupleSize = 62

-- | 'the' ensures that all the elements of the list are identical
-- and then returns that unique element
the :: Eq a => [a] -> a
the (x:xs)
  | all (x ==) xs = x
  | otherwise     = error "GHC.Exts.the: non-identical elements"
the []            = error "GHC.Exts.the: empty list"

-- | The 'sortWith' function sorts a list of elements using the
-- user supplied function to project something out of each element
sortWith :: Ord b => (a -> b) -> [a] -> [a]
sortWith f = sortBy (\x y -> compare (f x) (f y))

-- | The 'groupWith' function uses the user supplied function which
-- projects an element out of every list element in order to first sort the
-- input list and then to form groups by equality on these projected elements
{-# INLINE groupWith #-}
groupWith :: Ord b => (a -> b) -> [a] -> [[a]]
groupWith f xs = build (\c n -> groupByFB c n (\x y -> f x == f y) (sortWith f xs))

groupByFB :: ([a] -> lst -> lst) -> lst -> (a -> a -> Bool) -> [a] -> lst
groupByFB c n eq xs0 = groupByFBCore xs0
  where groupByFBCore [] = n
        groupByFBCore (x:xs) = c (x:ys) (groupByFBCore zs)
            where (ys, zs) = span (eq x) xs


-- -----------------------------------------------------------------------------
-- tracing

traceEvent :: String -> IO ()
traceEvent = Debug.Trace.traceEventIO
{-# DEPRECATED traceEvent "Use 'Debug.Trace.traceEvent' or 'Debug.Trace.traceEventIO'" #-} -- deprecated in 7.4


{- **********************************************************************
*									*
*              SpecConstr annotation                                    *
*									*
********************************************************************** -}

-- Annotating a type with NoSpecConstr will make SpecConstr
-- not specialise for arguments of that type.

-- This data type is defined here, rather than in the SpecConstr module
-- itself, so that importing it doesn't force stupidly linking the
-- entire ghc package at runtime

data SpecConstrAnnotation = NoSpecConstr | ForceSpecConstr
                deriving( Data, Typeable, Eq )


{- **********************************************************************
*									*
*              The IsList class                                         *
*									*
********************************************************************** -}

-- | The 'IsList' class and its methods are intended to be used in
--   conjunction with the OverloadedLists extension.
--
-- /Since: 4.7.0.0/
class IsList l where
  -- | The 'Item' type function returns the type of items of the structure
  --   @l@.
  type Item l

  -- | The 'fromList' function constructs the structure @l@ from the given
  --   list of @Item l@
  fromList  :: [Item l] -> l

  -- | The 'fromListN' function takes the input list's length as a hint. Its
  --   behaviour should be equivalent to 'fromList'. The hint can be used to
  --   construct the structure @l@ more efficiently compared to 'fromList'. If
  --   the given hint does not equal to the input list's length the behaviour of
  --   'fromListN' is not specified.
  fromListN :: Int -> [Item l] -> l
  fromListN _ = fromList

  -- | The 'toList' function extracts a list of @Item l@ from the structure @l@.
  --   It should satisfy fromList . toList = id.
  toList :: l -> [Item l]

instance IsList [a] where
  type (Item [a]) = a
  fromList = id
  toList = id
