{-# LANGUAGE DeriveDataTypeable #-}{-# LANGUAGE DeriveGeneric #-}{-# LANGUAGE EmptyCase #-}{-# LANGUAGE EmptyDataDeriving #-}{-# LANGUAGE Safe #-}{-# LANGUAGE StandaloneDeriving #-}------------------------------------------------------------------------------- |-- Copyright : (C) 2008-2014 Edward Kmett-- License : BSD-style (see the file libraries/base/LICENSE)---- Maintainer : Edward Kmett <ekmett@gmail.com>-- Stability : provisional-- Portability : portable---- A logically uninhabited data type, used to indicate that a given-- term should not exist.---- @since 4.8.0.0----------------------------------------------------------------------------moduleData.Void(Void ,absurd ,vacuous )whereimportControl.Exception importData.Data importData.Ix importGHC.Generics importData.Semigroup (Semigroup (..),stimesIdempotent )-- | Uninhabited data type---- @since 4.8.0.0dataVoid deriving(Eq-- ^ @since 4.8.0.0,Data -- ^ @since 4.8.0.0,Generic -- ^ @since 4.8.0.0,Ord-- ^ @since 4.8.0.0,Read -- ^ Reading a 'Void' value is always a parse error, considering-- 'Void' as a data type with no constructors.---- @since 4.8.0.0,Show -- ^ @since 4.8.0.0)-- | @since 4.8.0.0instanceIx Void whererange :: (Void, Void) -> [Void]
range (Void, Void)
_=[]index :: (Void, Void) -> Void -> Int
index (Void, Void)
_=Void -> Int
forall a. Void -> a
absurd inRange :: (Void, Void) -> Void -> Bool
inRange (Void, Void)
_=Void -> Bool
forall a. Void -> a
absurd rangeSize :: (Void, Void) -> Int
rangeSize (Void, Void)
_=Int
0-- | @since 4.8.0.0instanceException Void -- | @since 4.9.0.0instanceSemigroup Void whereVoid
a <> :: Void -> Void -> Void
<> Void
_=Void
a stimes :: b -> Void -> Void
stimes =b -> Void -> Void
forall b a. Integral b => b -> a -> a
stimesIdempotent -- | Since 'Void' values logically don't exist, this witnesses the-- logical reasoning tool of \"ex falso quodlibet\".---- >>> let x :: Either Void Int; x = Right 5-- >>> :{-- case x of-- Right r -> r-- Left l -> absurd l-- :}-- 5---- @since 4.8.0.0absurd ::Void ->a absurd :: Void -> a
absurd Void
a =caseVoid
a of{}-- | If 'Void' is uninhabited then any 'Functor' that holds only-- values of type 'Void' is holding no values.---- Using @ApplicativeDo@: \'@'vacuous' theVoid@\' can be understood as the-- @do@ expression---- @-- do void <- theVoid-- pure (absurd void)-- @---- with an inferred @Functor@ constraint.---- @since 4.8.0.0vacuous ::Functor f =>f Void ->f a vacuous :: f Void -> f a
vacuous =(Void -> a) -> f Void -> f a
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap Void -> a
forall a. Void -> a
absurd