Copyright | (c) Andrey Mokhov 2018-2024 |
---|---|
License | MIT (see the file LICENSE) |
Maintainer | andrey.mokhov@gmail.com |
Stability | experimental |
Safe Haskell | Safe-Inferred |
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://dl.acm.org/doi/10.1145/3341694.
This module defines free rigid selective functors. Rigid selective functors
are those that satisfy the property <*> = apS
.
Intuitively, a selective functor f
is "rigid" if any expression f a
is
equivalent to a list of effects chained with select
operators (the normal
form given by the free construction). In contrast, "non-rigid" selective
functors can have non-linear, tree-like shapes, because *
nodes can't be
straightened using the <*> = apS
equation.
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.