https://github.com/fumieval/objective

Purely functional objects
https://github.com/fumieval/objective

Last synced: 26 days ago
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Purely functional objects

• Host: GitHub
• URL: https://github.com/fumieval/objective
• Owner: fumieval
• License: bsd-3-clause
• Created: 2014-09-18T08:17:45.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2021-10-27T11:01:05.000Z (about 3 years ago)
• Last Synced: 2024-12-09T21:29:04.284Z (about 1 month ago)
• Language: Haskell
• Homepage:
• Size: 174 KB
• Stars: 73
• Watchers: 12
• Forks: 6
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
objective

====

[![Hackage](https://img.shields.io/hackage/v/objective.svg)](https://hackage.haskell.org/package/objective) [![Build Status](https://secure.travis-ci.org/fumieval/objective.png?branch=master)](http://travis-ci.org/fumieval/objective)

Paper: https://fumieval.github.io/papers/en/2015-Haskell-objects.html

This package provides composable objects and instances.

Introduction

----

The primal construct, `Object`, models _object-oriented_ objects. `Object f g` represents an object.

```haskell

newtype Object f g = Object { runObject :: forall x. f x -> g (x, Object f g) }

```

An object interprets a message `f a` and returns the result `a` and the next object `Object f g`, on `g`.

```haskell

data Counter a where

  Increment :: Counter ()

  Print :: Counter Int

counter :: Int -> Object Counter IO

counter n = Object $ \case

  Increment -> return ((), counter (n + 1))

  Print -> print n >> return (n, counter n)

```

`new :: Object f g -> IO (Instance f g)` creates an instance of an object.

`(.-) :: (MonadIO m, MonadMask m) => Instance f m -> f a -> m a` sends a message to an instance. This can be used to handle instances in the typical OOP fashion.

```haskell

> i <- new (counter 0)

> i .- Increment

> i .- Print

1

> i .- Increment

> i .- Print

2

```

Interestingly, `Object (Skeleton t) m` and `Object t m` are isomorphic (`Skeleton` is an operational monad). `cascading` lets objects to handle an operational monad.