Data/Tuple.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}

-----------------------------------------------------------------------------
-- |
-- 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
 , snd
 , curry
 , uncurry
 , swap
 ) where

import GHC.Base () -- Note [Depend on GHC.Tuple]

default () -- Double isn't available yet

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

-- | 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)

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