https://github.com/chrispenner/selections
Haskell Package for operating with selections over an underlying functor
https://github.com/chrispenner/selections
Last synced: about 2 months ago
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Haskell Package for operating with selections over an underlying functor
- Host: GitHub
- URL: https://github.com/chrispenner/selections
- Owner: ChrisPenner
- License: bsd-3-clause
- Created: 2017-08-05T18:06:21.000Z (almost 8 years ago)
- Default Branch: master
- Last Pushed: 2020-10-21T02:55:38.000Z (over 4 years ago)
- Last Synced: 2024-04-25T23:02:25.093Z (about 1 year ago)
- Language: Haskell
- Size: 35.2 KB
- Stars: 22
- Watchers: 3
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
Selections
==========
[](https://hackage.haskell.org/package/selections)
[See it on Hackage](https://hackage.haskell.org/package/selections)
See also this library's [Scala port](https://github.com/ChristopherDavenport/selection) by **Christopher Davenport**
You'll probably want to start by reading the
[tutorial](https://github.com/ChrisPenner/selections/tree/master/tutorials/Basic.md).
`selections` is a haskell package for transforming subsets of values within a functor using
an intuitive selection-based interface.
Ever wished you could select just a few values within a functor, perform some
operations on them, then flatten them back into the plain old functor again? Now
you can!
`Selection` is a newtype wrapper around Functors which adds several
combinators and interesting instances. Wrapping a functor in `Selection` allows
you to:
- Select specific values within your functor according to a predicate
- Expand/Contract selections based on additional predicates using `include`
and `exclude`
- Select values based on their context if your functor is also a Comonad
- Map over unselected and/or selected values using `Bifunctor`
- Traverse over unselected and/or selected values using `Bitraversable`
- Fold over unselected and/or selected values using `Bifoldable`
- Perform monad computations over selected values if your functor is a Monad
- Extract all unselected or selected elements to a list
- Deselect and return to your original functor using `unify`
- Traverse or fold over selections using `Control.Lens`
Here's how it looks, tutorials are available
[here](https://github.com/ChrisPenner/selections/tree/master/tutorials).
```haskell
xs = [1..6]
λ> newSelection xs -- wrap `[Int]` into `Selection [] Int Int`, you can wrap any functor
& select even -- Focus on only even integers
& mapSelected (+100) -- Increment selected ints by 100
& bimap (("Odd: " ++) . show) (("Even: " ++) . show) -- map over unselected and selected values respectively
& forgetSelection -- Collapse back down to the underlying functor, in this case a list
["Odd: 1","Even: 102","Odd: 3","Even: 104","Odd: 5","Even: 106"]
```
Technically you could use `Selection` as a monad-transformer, but it's a bit
clunky and you'd probably be better off with
[`EitherT`](https://hackage.haskell.org/package/either-4.4.1.1/docs/Control-Monad-Trans-Either.html).
Fun fact, `Selection` is isomorphic to `EitherT`, but the semantics are quite
different and they're suited to different purposes.
## When Should/Shouldn't I Use Selections?
You can use selections whenever you've got a bunch of things and you want to operate over just a few of them at a time.
You can do everything that selections provides by combining a bunch of predicates with fmap, but it gets messy really
quick; selections provides a clean interface for this sort of operation.
You shouldn't use selections when you're looking for a monadic interface for this sort of thing, selections works
at the value level and typically you want to chain selection commands using `(.)` or `(&)`, it technically can
be used as a monad transformer if your underlying functor is also a monad, but at that point you may wish to check
out [`EitherT`](https://hackage.haskell.org/package/either-4.4.1.1/docs/Control-Monad-Trans-Either.html) instead.
## Examples
Check out the [Accounts
tutorial](https://github.com/ChrisPenner/selections/tree/master/tutorials/Basic.md)
first to get your bearings. After that continue to the [Lenses
tutorial](https://github.com/ChrisPenner/selections/tree/master/tutorials/Lenses.md).