diff options
| -rw-r--r-- | libraries/base/Data/Bifunctor.hs | 37 |
1 files changed, 36 insertions, 1 deletions
diff --git a/libraries/base/Data/Bifunctor.hs b/libraries/base/Data/Bifunctor.hs index 5441605ecf..04de5ad7f2 100644 --- a/libraries/base/Data/Bifunctor.hs +++ b/libraries/base/Data/Bifunctor.hs @@ -20,7 +20,15 @@ module Data.Bifunctor import Control.Applicative ( Const(..) ) import GHC.Generics ( K1(..) ) --- | Formally, the class 'Bifunctor' represents a bifunctor +-- | A bifunctor is a type constructor that takes +-- two type arguments and is a functor in /both/ arguments. That +-- is, unlike with 'Functor', a type constructor such as 'Either' +-- does not need to be partially applied for a 'Bifunctor' +-- instance, and the methods in this class permit mapping +-- functions over the 'Left' value or the 'Right' value, +-- or both at the same time. +-- +-- Formally, the class 'Bifunctor' represents a bifunctor -- from @Hask@ -> @Hask@. -- -- Intuitively it is a bifunctor where both the first and second @@ -59,22 +67,49 @@ class Bifunctor p where -- | Map over both arguments at the same time. -- -- @'bimap' f g ≡ 'first' f '.' 'second' g@ + -- + -- ==== __Examples__ + -- >>> bimap toUpper (+1) ('j', 3) + -- ('J',4) + -- + -- >>> bimap toUpper (+1) (Left 'j') + -- Left 'J' + -- + -- >>> bimap toUpper (+1) (Right 3) + -- Right 4 bimap :: (a -> b) -> (c -> d) -> p a c -> p b d bimap f g = first f . second g + -- | Map covariantly over the first argument. -- -- @'first' f ≡ 'bimap' f 'id'@ + -- + -- ==== __Examples__ + -- >>> first toUpper ('j', 3) + -- ('J',3) + -- + -- >>> first toUpper (Left 'j') + -- Left 'J' first :: (a -> b) -> p a c -> p b c first f = bimap f id + -- | Map covariantly over the second argument. -- -- @'second' ≡ 'bimap' 'id'@ + -- + -- ==== __Examples__ + -- >>> second (+1) ('j', 3) + -- ('j',4) + -- + -- >>> second (+1) (Right 3) + -- Right 4 second :: (b -> c) -> p a b -> p a c second = bimap id + -- | @since 4.8.0.0 instance Bifunctor (,) where bimap f g ~(a, b) = (f a, g b) |