https://github.com/fused-effects/fused-effects-lens

Lens combinators for fused-effects.
https://github.com/fused-effects/fused-effects-lens

Last synced: 2 months ago
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Lens combinators for fused-effects.

• Host: GitHub
• URL: https://github.com/fused-effects/fused-effects-lens
• Owner: fused-effects
• License: bsd-3-clause
• Created: 2018-12-18T23:19:36.000Z (about 6 years ago)
• Default Branch: master
• Last Pushed: 2020-10-19T18:51:42.000Z (about 4 years ago)
• Last Synced: 2024-10-05T01:46:32.064Z (3 months ago)
• Language: Haskell
• Homepage: http://hackage.haskell.org/package/fused-effects-lens
• Size: 33.2 KB
• Stars: 17
• Watchers: 3
• Forks: 4
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGES.md
  • License: LICENSE

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README

        
# fused-effects-lens

[![Hackage](https://img.shields.io/hackage/v/fused-effects-lens.svg)](https://hackage.haskell.org/package/fused-effects-lens)

[![BSD3 license](https://img.shields.io/badge/license-BSD3-blue.svg)](LICENSE)

[![Build Status](https://action-badges.now.sh/fused-effects/fused-effects-lens)](https://github.com/fused-effects/fused-effects-lens/actions)

This package provides an interface to the [`lens`](https://github.com/ekmett/lens) library (and other such libraries such as `microlens` and `generic-lens`) that is compatible with [`fused-effects`](https://github.com/robrix/fused-effects). The standard formulation of `lens` combinators for operating in `MonadState` contexts—`use`, `.=`, et al—rely on `mtl` for `MonadState` and `MonadReader`, which is not applicable to `Reader` and `State` effects.

This package is meant to be used alongside `lens`, like so:

``` haskell

import Control.Lens hiding (view, use, assign)

import Control.Effect.Lens (view, use, assign)

```

## Example

Given a `Context` type that we will use in a `State` effect:

``` haskell

data Context = Context

  { _amount :: Int

  , _disabled :: Bool

  } deriving (Eq, Show)

makeLenses ''Context

```

We can can use the `use` combinators to extract a lens target from the current state, and `assign` to write to a field of that state:

``` haskell

stateTest :: (Has (State Context) sig m) => m Int

stateTest = do

  initial <- use amount

  amount .= (initial + 1)

  disabled .= True

  use amount

```

You can find a more complete example, including one that works with multiple `State` constraints in a single computation, in the `test` directory.

## License

BSD3, like `fused-effects`.