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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Modulebase-4.20.2.0Haskell2010

Data.Functor.Const

  • 1 type
  • Packagebase-4.20.2.0
  • Exports1
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceConst.hs
newtypenewtype Const a (b :: k)
#

The Const functor.

Examples
Example1 expression
fmap (++ "World") (Const "Hello")Const "Hello"

Because we ignore the second type parameter to Const, the Applicative instance, which has (<*>) :: Monoid m => Const m (a -> b) -> Const m a -> Const m b essentially turns into Monoid m => m -> m -> m, which is (<>)

Example1 expression
Const [1, 2, 3] <*> Const [4, 5, 6]Const [1,2,3,4,5,6]

Constructors

Instances42Generic1, Bifoldable, Bifoldable1, Bifunctor, Bitraversable, Eq2, …