{-# 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)