widmogrod/php-algorithm-w

# Algorithm W in PHP 
[![Build Status](https://travis-ci.org/widmogrod/php-algorithm-w.svg?branch=master)](https://travis-ci.org/widmogrod/php-algorithm-w) 
[![Maintainability](https://api.codeclimate.com/v1/badges/70bd6fed8962454e4c70/maintainability)](https://codeclimate.com/github/widmogrod/php-algorithm-w/maintainability)
[![Test Coverage](https://api.codeclimate.com/v1/badges/70bd6fed8962454e4c70/test_coverage)](https://codeclimate.com/github/widmogrod/php-algorithm-w/test_coverage)

## Introduction

Yet another fascinating concept to explore - `type interference`.

`Algorithm W` was implemented in PHP, and is based on **Martin Grabmüller** work [1].

Project uses the `php-functional` library `[2]` to simplify implementation, and make it closer to `Haskell`.

Next step is to use gathered experience it the [typed-config](https://github.com/widmogrod/typed-config) project `[3]`,
with is aiming to make configuration type safe, self-documenting, easy to extend and dead-simple to use.

Sneak peek of one of [many test cases](./src/AlgorithmW/AlgorithmWTest.php) can be interpreted
```php
'let id = (x -> let y = x in y) in id id ' => [
    'expression' => new ELet(
        'id',
        new EAbs(
            'x',
            new ELet(
                'y',
                new EVar('x'),
                new EVar('y')
            )
        ),
        new EApp(
            new EVar('id'),
            new EVar('id')
        )
    ),
    'expected' => '(a5 -> a5)',
],
```

## References
- `[1]` [Algorithm W Step by Step](https://github.com/mgrabmueller/AlgorithmW)
- `[2]` [php-functional](https://github.com/widmogrod/php-functional)
- `[3]` [typed-config](https://github.com/widmogrod/typed-config)