Copyright	(C) 2011-2013 Edward Kmett,
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	provisional
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

Data.Profunctor

Contents

Profunctors

Description

For a good explanation of profunctors in Haskell see Dan Piponi's article:

http://blog.sigfpe.com/2011/07/profunctors-in-haskell.html

For more information on strength and costrength, see:

http://comonad.com/reader/2008/deriving-strength-from-laziness/

Synopsis

Profunctors

class Profunctor p where Source

Formally, the class Profunctor represents a profunctor from Hask -> Hask.

Intuitively it is a bifunctor where the first argument is contravariant and the second argument is covariant.

You can define a Profunctor by either defining dimap or by defining both lmap and rmap.

If you supply dimap, you should ensure that:

dimap id id ≡ id

If you supply lmap and rmap, ensure:

lmap id ≡ id
rmap id ≡ id

If you supply both, you should also ensure:

dimap f g ≡ lmap f . rmap g

These ensure by parametricity:

dimap (f . g) (h . i) ≡ dimap g h . dimap f i
lmap (f . g) ≡ lmap g . lmap f
rmap (f . g) ≡ rmap f . rmap g

Minimal complete definition

dimap | lmap, rmap

Methods

dimap :: (a -> b) -> (c -> d) -> p b c -> p a d Source

Map over both arguments at the same time.

dimap f g ≡ lmap f . rmap g

lmap :: (a -> b) -> p b c -> p a c Source

Map the first argument contravariantly.

lmap f ≡ dimap f id

rmap :: (b -> c) -> p a b -> p a c Source

Map the second argument covariantly.

rmap ≡ dimap id

Instances

Profunctor (->)
Monad m => Profunctor (Kleisli m)
Functor w => Profunctor (Cokleisli w)
Profunctor (Tagged *)
Profunctor (Forget r)
Arrow p => Profunctor (WrappedArrow p)
Functor f => Profunctor (DownStar f)
Functor f => Profunctor (UpStar f)
Profunctor p => Profunctor (Environment p)
Profunctor p => Profunctor (Closure p)
Profunctor p => Profunctor (Codensity p)
Profunctor p => Profunctor (Copastro p)
Profunctor p => Profunctor (Cotambara p)
Profunctor p => Profunctor (Pastro p)
Profunctor p => Profunctor (Tambara p)
(Functor f, Profunctor p) => Profunctor (Cayley f p)
(Profunctor p, Profunctor q) => Profunctor (Rift p q)
(Profunctor p, Profunctor q) => Profunctor (Procompose p q)
(Profunctor p, Profunctor q) => Profunctor (Ran p q)

Profunctorial Strength

class Profunctor p => Strong p where Source

Generalizing UpStar of a strong Functor

Note: Every Functor in Haskell is strong with respect to (,).

This describes profunctor strength with respect to the product structure of Hask.

http://takeichi.ipl-lab.org/~asada/papers/arrStrMnd.pdf

Minimal complete definition

first' | second'

Methods

first' :: p a b -> p (a, c) (b, c) Source

second' :: p a b -> p (c, a) (c, b) Source

Instances

Strong (->)
Monad m => Strong (Kleisli m)
Strong (Forget r)
Arrow p => Strong (WrappedArrow p)	Every Arrow is a Strong Monad in Prof
Functor m => Strong (UpStar m)
Strong p => Strong (Closure p)
Profunctor p => Strong (Tambara p)
(Functor f, Strong p) => Strong (Cayley f p)
(Strong p, Strong q) => Strong (Procompose p q)

class Profunctor p => Choice p where Source

The generalization of DownStar of Functor that is strong with respect to Either.

Note: This is also a notion of strength, except with regards to another monoidal structure that we can choose to equip Hask with: the cocartesian coproduct.

Minimal complete definition

left' | right'

Methods

left' :: p a b -> p (Either a c) (Either b c) Source

right' :: p a b -> p (Either c a) (Either c b) Source

Instances

Choice (->)
Monad m => Choice (Kleisli m)
Comonad w => Choice (Cokleisli w)	`extract` approximates `costrength`
Choice (Tagged *)
Monoid r => Choice (Forget r)
ArrowChoice p => Choice (WrappedArrow p)
Traversable w => Choice (DownStar w)
Applicative f => Choice (UpStar f)
Profunctor p => Choice (Cotambara p)
Choice p => Choice (Tambara p)
(Functor f, Choice p) => Choice (Cayley f p)
(Choice p, Choice q) => Choice (Procompose p q)

Profunctorial Costrength

class Profunctor p => Costrong p where Source

Analogous to ArrowLoop, loop = unfirst

unfirst . unfirst =

Minimal complete definition

Nothing

Methods

unfirst :: p (a, d) (b, d) -> p a b Source

unsecond :: p (d, a) (d, b) -> p a b Source

Instances

Costrong (->)
MonadFix m => Costrong (Kleisli m)
Costrong (Tagged *)
ArrowLoop p => Costrong (WrappedArrow p)

class Profunctor p => Cochoice p where Source

Minimal complete definition

Nothing

Methods

unleft :: p (Either a d) (Either b d) -> p a b Source

unright :: p (Either d a) (Either d b) -> p a b Source

Common Profunctors

newtype UpStar f d c Source

Lift a Functor into a Profunctor (forwards).

Constructors

UpStar
Fields runUpStar :: d -> f c

Instances

Functor f => Profunctor (UpStar f)
Applicative f => Choice (UpStar f)
Functor m => Strong (UpStar m)
Distributive f => Closed (UpStar f)
Functor f => Representable (UpStar f)
Alternative f => Alternative (UpStar f a)
Monad f => Monad (UpStar f a)
Functor f => Functor (UpStar f a)
MonadPlus f => MonadPlus (UpStar f a)
Applicative f => Applicative (UpStar f a)
type Rep (UpStar f) = f

newtype DownStar f d c Source

Lift a Functor into a Profunctor (backwards).

Constructors

DownStar
Fields runDownStar :: f d -> c

Instances

Functor f => Profunctor (DownStar f)
Traversable w => Choice (DownStar w)
Functor f => Closed (DownStar f)
Functor f => Corepresentable (DownStar f)
Monad (DownStar f a)
Functor (DownStar f a)
Applicative (DownStar f a)
type Corep (DownStar f) = f

newtype WrappedArrow p a b Source

Wrap an arrow for use as a Profunctor.

Constructors

WrapArrow
Fields unwrapArrow :: p a b

Instances

Category * p => Category * (WrappedArrow p)
Arrow p => Arrow (WrappedArrow p)
ArrowZero p => ArrowZero (WrappedArrow p)
ArrowChoice p => ArrowChoice (WrappedArrow p)
ArrowApply p => ArrowApply (WrappedArrow p)
ArrowLoop p => ArrowLoop (WrappedArrow p)
Arrow p => Profunctor (WrappedArrow p)
ArrowLoop p => Costrong (WrappedArrow p)
ArrowChoice p => Choice (WrappedArrow p)
Arrow p => Strong (WrappedArrow p)	Every Arrow is a Strong Monad in Prof

newtype Forget r a b Source

Constructors

Forget
Fields runForget :: a -> r

Instances

Profunctor (Forget r)
Monoid r => Choice (Forget r)
Strong (Forget r)
Representable (Forget r)
Functor (Forget r a)
Foldable (Forget r a)
Traversable (Forget r a)
type Rep (Forget r) = Const r

type (:->) p q = forall a b. p a b -> q a b infixr 0 Source