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https://github.com/kowainik/validation-selective
💂♂️ Lightweight pure validation based on Applicative and Selective functors
https://github.com/kowainik/validation-selective
applicative functors haskell haskell-libraries selective validation
Last synced: 3 months ago
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💂♂️ Lightweight pure validation based on Applicative and Selective functors
- Host: GitHub
- URL: https://github.com/kowainik/validation-selective
- Owner: kowainik
- License: mpl-2.0
- Created: 2020-03-05T20:38:50.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2024-05-11T16:37:47.000Z (9 months ago)
- Last Synced: 2024-10-02T16:47:18.502Z (4 months ago)
- Topics: applicative, functors, haskell, haskell-libraries, selective, validation
- Language: Haskell
- Homepage: https://kowainik.github.io/projects/validation-selective
- Size: 93.8 KB
- Stars: 66
- Watchers: 7
- Forks: 11
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
- Codeowners: .github/CODEOWNERS
Awesome Lists containing this project
README
# validation-selective
[](https://github.com/kowainik/validation-selective/actions)
[](https://hackage.haskell.org/package/validation-selective)
[](LICENSE)
Lightweight pure data validation based on `Applicative` and `Selective` functors.
`validation-selective` is built around the following data type:
```haskell
data Validation e a
= Failure e
| Success a
```
This data type is similar to `Either` but allows accumulating all
errors instead of short-circuiting on the first one.
For more examples and library tutorial, refer to Haddock:
* [`validation`: Official documentation](http://hackage.haskell.org/package/validation-selective/docs/Validation.html)
## Comparison with other packages
`validation-selective` is not the only package that provides such
`Validation` data type. However, unlike other packages, it has some
noticeable advantages:
+ **Lightweight**. `validation-selective` depends only on `base` and
`selective` (which is tiny) Haskell libraries which make this
package fast to build. So adding validation capabilities to your
library or application doesn't contribute much to your dependency
footprint.
+ **Selective instance.** `validation-selective` is the only package
that provides `Selective` instance for `Validation` which allows
using `Monad`-like branching behaviour but without implementing
wrong `Monad` instance.
+ **More algebraic instances.** `validation-selective` also provides
the `Alternative` instance and a more general `Semigroup` instance.
+ **Best-in-class documentation.** Official Haddock documentation
contains mini-tutorial, usage example, per-component comparison with
`Either`, the motivation behind each instance and the interface in
general along with examples for **each instance and function**.
The below section provides per-package comparison with the most
popular validation packages in the Haskell ecosystem:
+ [`either`](https://hackage.haskell.org/package/either): `Validation`
implementation by Edward Kmett. This package is more heavyweight,
since it depends on more Haskell libraries like `profunctors`,
`bifunctors`, `semigroupoids`. But it also provides prisms for
`Validation` and some combinators for `Either`.
+ [`validation`](https://hackage.haskell.org/package/validation):
`Validation` from [Queensland Functional Programming Lab](https://qfpl.io/).
Depends on `lens`, which makes it even heavier but also have richer
interface compared to the `either` package.
## How to use
`validation-selective` is compatible with the latest GHC compiler
versions starting from `8.6`.
In order to start using `validation-selective` in your project, you
will need to set it up with the three easy steps:
1. Add the dependency on `validation-selective` in your project's
`.cabal` file. For this, you should modify the `build-depends`
section by adding the name of this library. After the adjustment,
this section could look like this:
```haskell
build-depends: base ^>= 4.14
, validation-selective ^>= 0.0
```
2. In the module where you wish to implement pure data validation, you
should add the import:
```haskell
import Validation (Validation (..))
```
3. Now you can use the types and functions from the library:
```haskell
main :: IO ()
main = print [Failure "wrong", Success 42]
```
### Usage with Stack
If `validation-selective` is not available on your current Stackage
resolver yet, fear not! You can still use it from Hackage by adding
the following to the `extra-deps` section of your `stack.yaml` file:
```yaml
extra-deps:
- validation-selective-CURRENT_VERSION
```