Copyright	(C) 2008-2014 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	libraries@haskell.org
Stability	provisional
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Data.Bifunctor

Description

Since: 4.8.0.0

Synopsis

class Bifunctor p where
- bimap :: (a -> b) -> (c -> d) -> p a c -> p b d
- first :: (a -> b) -> p a c -> p b c
- second :: (b -> c) -> p a b -> p a c

Documentation

class Bifunctor p where Source #

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 arguments are covariant.

You can define a Bifunctor by either defining bimap or by defining both first and second .

If you supply bimap , you should ensure that:

bimap  id  id  ≡ id

If you supply first and second , ensure:

first  id  ≡ id 
second  id  ≡ id

If you supply both, you should also ensure:

bimap  f g ≡ first  f .  second  g

These ensure by parametricity:

bimap  (f .  g) (h .  i) ≡ bimap  f h .  bimap  g i
first  (f .  g) ≡ first  f .  first  g
second  (f .  g) ≡ second  f .  second  g

Since: 4.8.0.0

Minimal complete definition

bimap | first, second

Methods

bimap :: (a -> b) -> (c -> d) -> p a c -> p b d Source #

Map over both arguments at the same time.

bimap  f g ≡ first  f .  second  g

Examples

Expand

>>> bimap toUpper (+1) ('j', 3)
('J',4)

>>> bimap toUpper (+1) (Left 'j')
Left 'J'

>>> bimap toUpper (+1) (Right 3)
Right 4

first :: (a -> b) -> p a c -> p b c Source #

Map covariantly over the first argument.

first  f ≡ bimap  f id

Examples

Expand

>>> first toUpper ('j', 3)
('J',3)

>>> first toUpper (Left 'j')
Left 'J'

second :: (b -> c) -> p a b -> p a c Source #

Map covariantly over the second argument.

second  ≡ bimap  id

Examples

Expand

>>> second (+1) ('j', 3)
('j',4)

>>> second (+1) (Right 3)
Right 4

Instances

Instances details

Bifunctor Either Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> Either a c -> Either b d Source #

first :: (a -> b) -> Either a c -> Either b c Source #

second :: (b -> c) -> Either a b -> Either a c Source #

Bifunctor (,) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (a, c) -> (b, d) Source #

first :: (a -> b) -> (a, c) -> (b, c) Source #

second :: (b -> c) -> (a, b) -> (a, c) Source #

Bifunctor Arg Source #

Since: 4.9.0.0

Instance details

Defined in Data.Semigroup

Methods

bimap :: (a -> b) -> (c -> d) -> Arg a c -> Arg b d Source #

first :: (a -> b) -> Arg a c -> Arg b c Source #

second :: (b -> c) -> Arg a b -> Arg a c Source #

Bifunctor ((,,) x1) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (x1, a, c) -> (x1, b, d) Source #

first :: (a -> b) -> (x1, a, c) -> (x1, b, c) Source #

second :: (b -> c) -> (x1, a, b) -> (x1, a, c) Source #

Bifunctor (Const :: Type -> Type -> Type) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> Const a c -> Const b d Source #

first :: (a -> b) -> Const a c -> Const b c Source #

second :: (b -> c) -> Const a b -> Const a c Source #

Bifunctor (K1 i :: Type -> Type -> Type) Source #

Since: 4.9.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> K1 i a c -> K1 i b d Source #

first :: (a -> b) -> K1 i a c -> K1 i b c Source #

second :: (b -> c) -> K1 i a b -> K1 i a c Source #

Bifunctor ((,,,) x1 x2) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (x1, x2, a, c) -> (x1, x2, b, d) Source #

first :: (a -> b) -> (x1, x2, a, c) -> (x1, x2, b, c) Source #

second :: (b -> c) -> (x1, x2, a, b) -> (x1, x2, a, c) Source #

Bifunctor ((,,,,) x1 x2 x3) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (x1, x2, x3, a, c) -> (x1, x2, x3, b, d) Source #

first :: (a -> b) -> (x1, x2, x3, a, c) -> (x1, x2, x3, b, c) Source #

second :: (b -> c) -> (x1, x2, x3, a, b) -> (x1, x2, x3, a, c) Source #

Bifunctor ((,,,,,) x1 x2 x3 x4) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (x1, x2, x3, x4, a, c) -> (x1, x2, x3, x4, b, d) Source #

first :: (a -> b) -> (x1, x2, x3, x4, a, c) -> (x1, x2, x3, x4, b, c) Source #

second :: (b -> c) -> (x1, x2, x3, x4, a, b) -> (x1, x2, x3, x4, a, c) Source #

Bifunctor ((,,,,,,) x1 x2 x3 x4 x5) Source #

Since: 4.8.0.0

Instance details

Defined in Data.Bifunctor

Methods

bimap :: (a -> b) -> (c -> d) -> (x1, x2, x3, x4, x5, a, c) -> (x1, x2, x3, x4, x5, b, d) Source #

first :: (a -> b) -> (x1, x2, x3, x4, x5, a, c) -> (x1, x2, x3, x4, x5, b, c) Source #

second :: (b -> c) -> (x1, x2, x3, x4, x5, a, b) -> (x1, x2, x3, x4, x5, a, c) Source #