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{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE 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
, snd
, curry
, uncurry
, swap
)
where
import GHC.Base
-- We need to depend on GHC.Base so that
-- a) so that we get GHC.Classes, 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
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)