Distribution/Compat/Prelude.hs

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE TypeOperators #-}
    {-# LANGUAGE RankNTypes #-}
    {-# LANGUAGE FlexibleContexts #-}

    #ifdef MIN_VERSION_base
    #define MINVER_base_48 MIN_VERSION_base(4,8,0)
    #define MINVER_base_47 MIN_VERSION_base(4,7,0)
    #define MINVER_base_46 MIN_VERSION_base(4,6,0)
    #else
    #define MINVER_base_48 (__GLASGOW_HASKELL__ >= 710)
    #define MINVER_base_47 (__GLASGOW_HASKELL__ >= 708)
    #define MINVER_base_46 (__GLASGOW_HASKELL__ >= 706)
    #endif

    -- | This module does two things:
    --
    -- * Acts as a compatiblity layer, like @base-compat@.
    --
    -- * Provides commonly used imports.
    module Distribution.Compat.Prelude (
        -- * Prelude
        --
        -- Prelude is re-exported, following is hidden:
        module BasePrelude,

    #if !MINVER_base_48
        -- * base 4.8 shim
        Applicative(..), (<$), (<$>),
        Monoid(..),
    #endif

        -- * Common type-classes
        Semigroup (..),
        gmappend, gmempty,
        Typeable,
        Data,
        Generic,
        NFData (..), genericRnf,
        Binary (..),
        Alternative (..),
        MonadPlus (..),
        IsString (..),

        -- * Some types
        IO, NoCallStackIO,
        Map,

        -- * Data.Maybe
        catMaybes, mapMaybe,
        fromMaybe,
        maybeToList, listToMaybe,
        isNothing, isJust,

        -- * Data.List
        unfoldr,
        isPrefixOf, isSuffixOf,
        intercalate, intersperse,
        sort, sortBy,
        nub, nubBy,

        -- * Data.Foldable
        Foldable, foldMap, foldr,
        null, length,
        find, foldl',
        traverse_, for_,

        -- * Data.Traversable
        Traversable, traverse, sequenceA,
        for,

        -- * Control.Arrow
        first,

        -- * Control.Monad
        liftM, liftM2,
        unless, when,
        ap, void,
        foldM, filterM,

        -- * Data.Char
        isSpace, isDigit, isUpper, isAlpha, isAlphaNum,
        chr, ord,
        toLower, toUpper,

        -- * Data.Word & Data.Int
        Word,
        Word8, Word16, Word32, Word64,
        Int8, Int16, Int32, Int64,

        -- * Text.PrettyPrint
        (<<>>),
        ) where

    -- We also could hide few partial function
    import Prelude                       as BasePrelude hiding
      ( IO, mapM, mapM_, sequence, null, length, foldr
    #if MINVER_base_48
      , Word
      -- We hide them, as we import only some members
      , Traversable, traverse, sequenceA
      , Foldable, foldMap
    #endif
      )

    #if !MINVER_base_48
    import Control.Applicative           (Applicative (..), (<$), (<$>))
    import Distribution.Compat.Semigroup (Monoid (..))
    #else
    import Data.Foldable                 (length, null)
    #endif

    import Data.Foldable                 (Foldable (foldMap, foldr), find, foldl', for_, traverse_)
    import Data.Traversable              (Traversable (traverse, sequenceA), for)

    import Control.Applicative           (Alternative (..))
    import Control.DeepSeq               (NFData (..))
    import Data.Data                     (Data)
    import Data.Typeable                 (Typeable)
    import Distribution.Compat.Binary    (Binary (..))
    import Distribution.Compat.Semigroup (Semigroup (..), gmappend, gmempty)
    import GHC.Generics                  (Generic, Rep(..),
                                          V1, U1(U1), K1(unK1), M1(unM1),
                                          (:*:)((:*:)), (:+:)(L1,R1))

    import Data.Map                      (Map)

    import Control.Arrow                 (first)
    import Control.Monad                 hiding (mapM)
    import Data.Char
    import Data.List                     (intercalate, intersperse, isPrefixOf,
                                          isSuffixOf, nub, nubBy, sort, sortBy,
                                          unfoldr)
    import Data.Maybe
    import Data.String                   (IsString (..))
    import Data.Int
    import Data.Word

    import qualified Text.PrettyPrint as Disp

    import qualified Prelude as OrigPrelude
    import Distribution.Compat.Stack

    type IO a = WithCallStack (OrigPrelude.IO a)
    type NoCallStackIO a = OrigPrelude.IO a

    -- | New name for 'Text.PrettyPrint.<>'
    (<<>>) :: Disp.Doc -> Disp.Doc -> Disp.Doc
    (<<>>) = (Disp.<>)

    #if !MINVER_base_48
    -- | Test whether the structure is empty. The default implementation is
    -- optimized for structures that are similar to cons-lists, because there
    -- is no general way to do better.
    null :: Foldable t => t a -> Bool
    null = foldr (\_ _ -> False) True

    -- | Returns the size/length of a finite structure as an 'Int'.  The
    -- default implementation is optimized for structures that are similar to
    -- cons-lists, because there is no general way to do better.
    length :: Foldable t => t a -> Int
    length = foldl' (\c _ -> c+1) 0
    #endif

    -- | "GHC.Generics"-based 'rnf' implementation
    --
    -- This is needed in order to support @deepseq < 1.4@ which didn't
    -- have a 'Generic'-based default 'rnf' implementation yet.
    --
    -- In order to define instances, use e.g.
    --
    -- > instance NFData MyType where rnf = genericRnf
    --
    -- The implementation has been taken from @deepseq-1.4.2@'s default
    -- 'rnf' implementation.
    genericRnf :: (Generic a, GNFData (Rep a)) => a -> ()
    genericRnf = grnf . from

    -- | Hidden internal type-class
    class GNFData f where
      grnf :: f a -> ()

    instance GNFData V1 where
      grnf = error "Control.DeepSeq.rnf: uninhabited type"

    instance GNFData U1 where
      grnf U1 = ()

    instance NFData a => GNFData (K1 i a) where
      grnf = rnf . unK1
      {-# INLINEABLE grnf #-}

    instance GNFData a => GNFData (M1 i c a) where
      grnf = grnf . unM1
      {-# INLINEABLE grnf #-}

    instance (GNFData a, GNFData b) => GNFData (a :*: b) where
      grnf (x :*: y) = grnf x `seq` grnf y
      {-# INLINEABLE grnf #-}

    instance (GNFData a, GNFData b) => GNFData (a :+: b) where
      grnf (L1 x) = grnf x
      grnf (R1 x) = grnf x
      {-# INLINEABLE grnf #-}