{-# LANGUAGE DeriveGeneric #-}{-# LANGUAGE GeneralizedNewtypeDeriving #-}{-# LANGUAGE NoImplicitPrelude #-}{-# LANGUAGE PolyKinds #-}{-# LANGUAGE ScopedTypeVariables #-}{-# LANGUAGE Trustworthy #-}------------------------------------------------------------------------------- |-- Module : Data.Functor.Const-- Copyright : Conor McBride and Ross Paterson 2005-- License : BSD-style (see the LICENSE file in the distribution)---- Maintainer : libraries@haskell.org-- Stability : experimental-- Portability : portable-- The 'Const' functor.---- @since 4.9.0.0moduleData.Functor.Const(Const (..))whereimportData.Bits (Bits ,FiniteBits )importData.Foldable (Foldable (foldMap ))importForeign.Storable (Storable )importGHC.Ix (Ix )importGHC.Base importGHC.Enum (Bounded ,Enum )importGHC.Float (Floating ,RealFloat )importGHC.Generics (Generic ,Generic1 )importGHC.Num (Num )importGHC.Real (Fractional ,Integral ,Real ,RealFrac )importGHC.Read (Read (readsPrec ),readParen ,lex )importGHC.Show (Show (showsPrec ),showParen ,showString )-- | The 'Const' functor.newtypeConst a b =Const {Const a b -> a
getConst ::a }deriving(Bits -- ^ @since 4.9.0.0,Bounded -- ^ @since 4.9.0.0,Enum -- ^ @since 4.9.0.0,Eq-- ^ @since 4.9.0.0,FiniteBits -- ^ @since 4.9.0.0,Floating -- ^ @since 4.9.0.0,Fractional -- ^ @since 4.9.0.0,Generic -- ^ @since 4.9.0.0,Generic1 -- ^ @since 4.9.0.0,Integral -- ^ @since 4.9.0.0,Ix -- ^ @since 4.9.0.0,Semigroup -- ^ @since 4.9.0.0,Monoid -- ^ @since 4.9.0.0,Num -- ^ @since 4.9.0.0,Ord-- ^ @since 4.9.0.0,Real -- ^ @since 4.9.0.0,RealFrac -- ^ @since 4.9.0.0,RealFloat -- ^ @since 4.9.0.0,Storable -- ^ @since 4.9.0.0)-- | This instance would be equivalent to the derived instances of the-- 'Const' newtype if the 'getConst' field were removed---- @since 4.8.0.0instanceRead a =>Read (Const a b )wherereadsPrec :: Int -> ReadS (Const a b)
readsPrec Int
d =Bool -> ReadS (Const a b) -> ReadS (Const a b)
forall a. Bool -> ReadS a -> ReadS a
readParen (Int
d Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
>Int
10)(ReadS (Const a b) -> ReadS (Const a b))
-> ReadS (Const a b) -> ReadS (Const a b)
forall a b. (a -> b) -> a -> b
$ \String
r ->[(a -> Const a b
forall k a (b :: k). a -> Const a b
Const a
x ,String
t )|(String
"Const",String
s )<-ReadS String
lex String
r ,(a
x ,String
t )<-Int -> ReadS a
forall a. Read a => Int -> ReadS a
readsPrec Int
11String
s ]-- | This instance would be equivalent to the derived instances of the-- 'Const' newtype if the 'getConst' field were removed---- @since 4.8.0.0instanceShow a =>Show (Const a b )whereshowsPrec :: Int -> Const a b -> ShowS
showsPrec Int
d (Const a
x )=Bool -> ShowS -> ShowS
showParen (Int
d Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
>Int
10)(ShowS -> ShowS) -> ShowS -> ShowS
forall a b. (a -> b) -> a -> b
$ String -> ShowS
showString String
"Const "ShowS -> ShowS -> ShowS
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Int -> a -> ShowS
forall a. Show a => Int -> a -> ShowS
showsPrec Int
11a
x -- | @since 4.7.0.0instanceFoldable (Const m )wherefoldMap :: (a -> m) -> Const m a -> m
foldMap a -> m
_Const m a
_=m
forall a. Monoid a => a
mempty -- | @since 2.01instanceFunctor (Const m )wherefmap :: (a -> b) -> Const m a -> Const m b
fmap a -> b
_(Const m
v )=m -> Const m b
forall k a (b :: k). a -> Const a b
Const m
v -- | @since 2.0.1instanceMonoid m =>Applicative (Const m )wherepure :: a -> Const m a
pure a
_=m -> Const m a
forall k a (b :: k). a -> Const a b
Const m
forall a. Monoid a => a
mempty liftA2 :: (a -> b -> c) -> Const m a -> Const m b -> Const m c
liftA2 a -> b -> c
_(Const m
x )(Const m
y )=m -> Const m c
forall k a (b :: k). a -> Const a b
Const (m
x m -> m -> m
forall a. Monoid a => a -> a -> a
`mappend` m
y )<*> :: Const m (a -> b) -> Const m a -> Const m b
(<*>) =(m -> m -> m) -> Const m (a -> b) -> Const m a -> Const m b
coerce(m -> m -> m
forall a. Monoid a => a -> a -> a
mappend ::m ->m ->m )-- This is pretty much the same as-- Const f <*> Const v = Const (f `mappend` v)-- but guarantees that mappend for Const a b will have the same arity-- as the one for a; it won't create a closure to raise the arity-- to 2.