Copyright | (c) Andrey Mokhov 2018-2019 |
---|---|

License | MIT (see the file LICENSE) |

Maintainer | andrey.mokhov@gmail.com |

Stability | experimental |

Safe Haskell | None |

Language | Haskell2010 |

This is a library for *selective applicative functors*, or just
*selective functors* for short, an abstraction between applicative functors
and monads, introduced in this paper:
https://www.staff.ncl.ac.uk/andrey.mokhov/selective-functors.pdf.

This module defines *free rigid selective functors*. Rigid selective functors
are those that satisfy the property `<*> = apS`

.

## Synopsis

- data Select f a where
- liftSelect :: Functor f => f a -> Select f a
- getPure :: Select f a -> Maybe a
- getEffects :: Functor f => Select f a -> [f ()]
- getNecessaryEffect :: Functor f => Select f a -> Maybe (f ())
- runSelect :: Selective g => (forall x. f x -> g x) -> Select f a -> g a
- foldSelect :: Monoid m => (forall x. f x -> m) -> Select f a -> m

# Free rigid selective functors

data Select f a where Source #

Free rigid selective functors.

liftSelect :: Functor f => f a -> Select f a Source #

Lift a functor into a free selective computation.

# Static analysis

getPure :: Select f a -> Maybe a Source #

Extract the resulting value if there are no necessary effects.

getEffects :: Functor f => Select f a -> [f ()] Source #

Collect all possible effects in the order they appear in a free selective computation.

getNecessaryEffect :: Functor f => Select f a -> Maybe (f ()) Source #

Extract the necessary effect from a free selective computation. Note: there can be at most one effect that is statically guaranteed to be necessary.

runSelect :: Selective g => (forall x. f x -> g x) -> Select f a -> g a Source #

Given a natural transformation from `f`

to `g`

, this gives a canonical
natural transformation from `Select f`

to `g`

.

foldSelect :: Monoid m => (forall x. f x -> m) -> Select f a -> m Source #

Concatenate all effects of a free selective computation.