https://github.com/unkindpartition/monad-classes

A more flexible mtl
https://github.com/unkindpartition/monad-classes

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A more flexible mtl

• Host: GitHub
• URL: https://github.com/unkindpartition/monad-classes
• Owner: UnkindPartition
• License: mit
• Created: 2014-06-08T07:11:22.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2018-02-23T10:53:12.000Z (almost 7 years ago)
• Last Synced: 2024-10-22T04:21:20.629Z (3 months ago)
• Language: Haskell
• Homepage:
• Size: 71.3 KB
• Stars: 64
• Watchers: 13
• Forks: 11
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Contributing: CONTRIBUTING.md
  • License: LICENSE

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README

        
[![Build Status](https://travis-ci.org/feuerbach/monad-classes.svg?branch=master)](https://travis-ci.org/feuerbach/monad-classes)

See [this series of articles][1] for the detailed description and motivation.

[1]: https://ro-che.info/articles/extensible-effects

This is a more flexible version of mtl, the monad transformers library.

*   You can have many layers of e.g. state transformers in your stack, and

    you don't have to explicitly lift your `get`s and `put`s, as soon as

    different state transformers carry different types of states.

    Example:

    ``` haskell

    a :: (MonadState Bool m, MonadState Int m) => m ()

    a = do

      put False -- set the boolean state

      modify (+ (1 :: Int)) -- modify the integer state

    ```

*   mtl requires *Θ(n2)* instances (like `MonadReader e (StateT s m)`);

    monad-classes requires only *Θ(n)* of them (where *n* is the number of

    different transformer types).

    If you'd like to define your own monad-classes-style class, you have to

    write much less boilerplate code.

## The status of this repo

This repo serves two purposes:

* as a reference implementation accompanying the [series of articles on

  extensible effects][1]

* as an actual implementation we use at [Signal Vine](http://signalvine.com/)

While this is technically open source software, I am not interested in maintaining this as

an active open project. In practice this means that:

* this version of monad-classes is not on hackage

* I do not accept feature requests and pull requests. The exception is outright

  bugs; if you find any, please do report them.

There is a [hackage package][2] and a [repo][3] maintained by M Farkas-Dyck.

[2]: https://hackage.haskell.org/package/monad-classes

[3]: https://github.com/strake/monad-classes.hs