Data/Tuple.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE CPP, NoImplicitPrelude #-}
{-# OPTIONS_GHC -fno-warn-unused-imports #-}
-- XXX -fno-warn-unused-imports needed for the GHC.Tuple import below. Sigh.
-----------------------------------------------------------------------------
-- |
-- Module : Data.Tuple
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : portable
--
-- The tuple data types, and associated functions.
--
-----------------------------------------------------------------------------

module Data.Tuple
 ( fst -- :: (a,b) -> a
 , snd -- :: (a,b) -> a
 , curry -- :: ((a, b) -> c) -> a -> b -> c
 , uncurry -- :: (a -> b -> c) -> ((a, b) -> c)
 , swap -- :: (a,b) -> (b,a)
#ifdef __NHC__
 , (,)(..)
 , (,,)(..)
 , (,,,)(..)
 , (,,,,)(..)
 , (,,,,,)(..)
 , (,,,,,,)(..)
 , (,,,,,,,)(..)
 , (,,,,,,,,)(..)
 , (,,,,,,,,,)(..)
 , (,,,,,,,,,,)(..)
 , (,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,,,)(..)
#endif
 )
 where

#ifdef __GLASGOW_HASKELL__

import GHC.Base
-- We need to depend on GHC.Base so that
-- a) so that we get GHC.Classes, GHC.Ordering, GHC.Types

-- b) so that GHC.Base.inline is available, which is used
-- when expanding instance declarations

import GHC.Tuple
-- We must import GHC.Tuple, to ensure sure that the
-- data constructors of `(,)' are in scope when we do
-- the standalone deriving instance for Eq (a,b) etc

#endif /* __GLASGOW_HASKELL__ */

#ifdef __NHC__
import Prelude
import Prelude
 ( (,)(..)
 , (,,)(..)
 , (,,,)(..)
 , (,,,,)(..)
 , (,,,,,)(..)
 , (,,,,,,)(..)
 , (,,,,,,,)(..)
 , (,,,,,,,,)(..)
 , (,,,,,,,,,)(..)
 , (,,,,,,,,,,)(..)
 , (,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,,)(..)
 , (,,,,,,,,,,,,,,)(..)
 -- nhc98's prelude only supplies tuple instances up to size 15
 , fst, snd
 , curry, uncurry
 )
#endif

#ifdef __GLASGOW_HASKELL__
import GHC.Unit ()
#endif

default () -- Double isn't available yet

-- ---------------------------------------------------------------------------
-- Standard functions over tuples

#if !defined(__HUGS__) && !defined(__NHC__)
-- | Extract the first component of a pair.
fst :: (a,b) -> a
fst (x,_) = x

-- | Extract the second component of a pair.
snd :: (a,b) -> b
snd (_,y) = y

-- | 'curry' converts an uncurried function to a curried function.
curry :: ((a, b) -> c) -> a -> b -> c
curry f x y = f (x, y)

-- | 'uncurry' converts a curried function to a function on pairs.
uncurry :: (a -> b -> c) -> ((a, b) -> c)
uncurry f p = f (fst p) (snd p)
#endif /* neither __HUGS__ nor __NHC__ */

-- | Swap the components of a pair.
swap :: (a,b) -> (b,a)
swap (a,b) = (b,a)