https://github.com/coot/free-category

Free categories, free arrows and free categories with monadic actions
https://github.com/coot/free-category

category free state-machine

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Free categories, free arrows and free categories with monadic actions

• Host: GitHub
• URL: https://github.com/coot/free-category
• Owner: coot
• License: mpl-2.0
• Created: 2018-10-21T22:10:52.000Z (about 6 years ago)
• Default Branch: master
• Last Pushed: 2023-06-04T11:27:49.000Z (over 1 year ago)
• Last Synced: 2024-04-25T12:44:07.784Z (9 months ago)
• Topics: category, free, state-machine
• Language: Haskell
• Homepage: https://hackage.haskell.org/package/free-category
• Size: 277 KB
• Stars: 22
• Watchers: 4
• Forks: 2
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • Changelog: ChangeLog.md
  • License: LICENSE

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README

        
# Free Category

[![Maintainer: coot](https://img.shields.io/badge/maintainer-coot-lightgrey.svg?style=for-the-badge)](http://github.com/coot)

[![Haskell/CI](https://img.shields.io/github/actions/workflow/status/coot/free-category/ci.yaml?branch=master&label=Build&style=for-the-badge)](https://github.com/coot/free-category/actions)

This package contains efficient implementations of free categories. There are

various representations available:

* real-time queues (C. Okasaki 'Pure Functional Data Structures')

* type aligned lists

* continuation passing style (Church encoding)

Free arrows and free Kleisli categories are also included.

Free categories are useful to model state machines in a simple yet type safe

manner.  For that purpose `Kleisli` categories are a very useful target which

allows to include monadic computations.  This package contains a useful

generalisation of `Kleisli` categories captured by `EffectCategory` class

(categories with effects), and a (free) transformer which lifts a category to

a category with effects.

## Benchmarks

Check performance characteristics of various representations:

* [report-O0](/bench/report-O0.md)

* [report-O1](/bench/report-O1.md)

* [report-O2](/bench/report-O2.md)

## Resources

* [LoginStateMachine](https://github.com/coot/free-category/blob/master/examples/src/LoginStateMachine.hs):

  based on [State Machines All The Way

  Down](https://www.youtube.com/watch?v=xq7ZuSRgCR4) by Edwin Bradly, 2017.

  You can run it with `cabal new-run examples:login-state-machine`.

* Read more [here](https://coot.me/posts/finite-state-machines.html) on

  a simple example of a finite state machine encoded using a free category

  using a simple GADT.

* Another

  [example](https://github.com/coot/free-algebras/blob/master/examples/src/Control/Category/Free.hs).

* [Blog post](https://coot.me/posts/kleisli-categories-and-free-monads.html) on Kleisli categories.