Modulebase-4.23.0.0Haskell2010

Data.Void

A logically uninhabited data type, used to indicate that a given term should not exist.

Synopsis

datadata Void

Uninhabited data type

Instances11Eq, Data, Ord, Read, Show, Ix, …

Eq VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Base
Data VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Data
Ord VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Base
Read VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Read
Reading a Void value is always a parse error, considering Void as a data type with no constructors.
Show VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Show
Ix VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Ix
Generic VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Generics
Semigroup VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Base
Exception VoidDefined in ghc-internal-10.0.0 · GHC.Internal.Exception.Type
Lift VoidDefined in ghc-internal-10.0.0 · GHC.Internal.TH.Lift
type Rep Void = D1 ('MetaData "Void" "GHC.Internal.Base" "ghc-internal" 'False) V1Defined in ghc-internal-10.0.0 · GHC.Internal.Generics

valueabsurd :: Void -> a

Since Void values logically don't exist, this witnesses the logical reasoning tool of "ex falso quodlibet".

Example2 expressions

>>> let x :: Either Void Int; x = Right 5>>> :{case x of    Right r -> r    Left l  -> absurd l:}5

valuevacuous :: Functor f => f Void -> f a

If Void is uninhabited then any Functor that holds only values of type Void is holding no values. It is implemented in terms of fmap absurd.