Portability | portable |
---|---|

Stability | provisional |

Maintainer | Edward Kmett <ekmett@gmail.com> |

Safe Haskell | Safe-Inferred |

- class Functor g => Distributive g where
- distribute :: Functor f => f (g a) -> g (f a)
- collect :: Functor f => (a -> g b) -> f a -> g (f b)
- distributeM :: Monad m => m (g a) -> g (m a)
- collectM :: Monad m => (a -> g b) -> m a -> g (m b)

- cotraverse :: (Functor f, Distributive g) => (f a -> b) -> f (g a) -> g b
- comapM :: (Monad m, Distributive g) => (m a -> b) -> m (g a) -> g b

# Documentation

class Functor g => Distributive g whereSource

This is the categorical dual of `Traversable`

.

Due to the lack of non-trivial comonoids in Haskell, we can restrict
ourselves to requiring a `Functor`

rather than
some Coapplicative class. Categorically every `Distributive`

functor is actually a right adjoint, and so it must be `Representable`

endofunctor and preserve all limits. This is a fancy way of saying it
isomorphic to `(->) x` for some x.

Minimal complete definition: `distribute`

or `collect`

To be distributable a container will need to have a way to consistently zip a potentially infinite number of copies of itself. This effectively means that the holes in all values of that type, must have the same cardinality, fixed sized vectors, infinite streams, functions, etc. and no extra information to try to merge together.

distribute :: Functor f => f (g a) -> g (f a)Source

collect :: Functor f => (a -> g b) -> f a -> g (f b)Source

`collect`

f =`distribute`

.`fmap`

f

distributeM :: Monad m => m (g a) -> g (m a)Source

The dual of `sequence`

`distributeM`

=`fmap`

`unwrapMonad`

.`distribute`

.`WrapMonad`

collectM :: Monad m => (a -> g b) -> m a -> g (m b)Source

`collectM`

=`distributeM`

.`liftM`

f

Distributive Identity | |

Distributive ((->) e) | |

Distributive f => Distributive (Backwards f) | |

Distributive g => Distributive (IdentityT g) | |

Distributive f => Distributive (Reverse f) | |

Distributive g => Distributive (ReaderT e g) | |

(Distributive f, Distributive g) => Distributive (Compose f g) | |

(Distributive f, Distributive g) => Distributive (Product f g) |

cotraverse :: (Functor f, Distributive g) => (f a -> b) -> f (g a) -> g bSource

The dual of `traverse`

`cotraverse`

f =`fmap`

f .`distribute`

comapM :: (Monad m, Distributive g) => (m a -> b) -> m (g a) -> g bSource

The dual of `mapM`

`comapM`

f =`fmap`

f .`distributeM`