| Copyright | (C) 2011 Edward Kmett |
|---|---|
| License | BSD-style (see the file LICENSE) |
| Maintainer | Edward Kmett <ekmett@gmail.com> |
| Stability | provisional |
| Portability | portable |
| Safe Haskell | Safe-Inferred |
| Language | Haskell98 |
Data.Distributive
Description
- 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 where
This is the categorical dual of Traversable. However, there appears
to be little benefit to allow the distribution via an arbitrary comonad
so we restrict ourselves to Functor.
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.
Minimal complete definition
Nothing
Methods
distribute :: Functor f => f (g a) -> g (f a)
The dual of sequence
distribute = collect id
collect :: Functor f => (a -> g b) -> f a -> g (f b)
collect = distribute . fmap f
distributeM :: Monad m => m (g a) -> g (m a)
distributeM = fmap unwrapMonad . distribute . WrapMonad
collectM :: Monad m => (a -> g b) -> m a -> g (m b)
collectM = distributeM . liftM f
Instances
| Distributive Identity | |
| Distributive ((->) e) | |
| Distributive g => Distributive (IdentityT g) | |
| 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 b
comapM :: (Monad m, Distributive g) => (m a -> b) -> m (g a) -> g b