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|
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE TypeFamilies #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.IsList
-- Copyright : (c) The University of Glasgow 2002
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC Extensions)
--
-- @since 4.17.0.0
-----------------------------------------------------------------------------
module GHC.IsList
( IsList(..)
) where
import GHC.Base
import GHC.Stack
import Data.Version ( Version(..), makeVersion )
import Control.Applicative (ZipList(..))
-- | The 'IsList' class and its methods are intended to be used in
-- conjunction with the OverloadedLists extension.
--
-- @since 4.7.0.0
class IsList l where
-- | The 'Item' type function returns the type of items of the structure
-- @l@.
type Item l
-- | The 'fromList' function constructs the structure @l@ from the given
-- list of @Item l@
fromList :: [Item l] -> l
-- | The 'fromListN' function takes the input list's length and potentially
-- uses it to construct the structure @l@ more efficiently compared to
-- 'fromList'. If the given number does not equal to the input list's length
-- the behaviour of 'fromListN' is not specified.
--
-- prop> fromListN (length xs) xs == fromList xs
fromListN :: Int -> [Item l] -> l
fromListN _ = fromList
-- | The 'toList' function extracts a list of @Item l@ from the structure @l@.
-- It should satisfy fromList . toList = id.
toList :: l -> [Item l]
-- | @since 4.7.0.0
instance IsList [a] where
type (Item [a]) = a
fromList = id
toList = id
-- | @since 4.15.0.0
instance IsList (ZipList a) where
type Item (ZipList a) = a
fromList = ZipList
toList = getZipList
-- | @since 4.9.0.0
instance IsList (NonEmpty a) where
type Item (NonEmpty a) = a
fromList (a:as) = a :| as
fromList [] = errorWithoutStackTrace "NonEmpty.fromList: empty list"
toList ~(a :| as) = a : as
-- | @since 4.8.0.0
instance IsList Version where
type (Item Version) = Int
fromList = makeVersion
toList = versionBranch
-- | Be aware that 'fromList . toList = id' only for unfrozen 'CallStack's,
-- since 'toList' removes frozenness information.
--
-- @since 4.9.0.0
instance IsList CallStack where
type (Item CallStack) = (String, SrcLoc)
fromList = fromCallSiteList
toList = getCallStack
|
