ADTs

Algebraic Data Types for Ruby.

Usage

Let’s define a Shape data type:

```ruby require ‘adts’

Shape = ADT do Void() | Square(width: Numeric) | Rectangle(width: Numeric, height: Numeric) | Circle(radius: Numeric) { def area Math::PI * radius * radius end } end ```

Let’s try to instantiate a Shape with our nullary constructor Void:

ruby Shape::Void() # => #<Shape::Void ...>

What about a square?

ruby Shape::Square(23) # => #<Shape::Square @width=23>

Our type constructors are even type-checked:

ruby Shape::Square("foo") # raises a TypeError

Our ADT implements equality by type and value:

ruby Shape::Square(23) == Shape::Square(23) # => true Shape::Circle(23) == Shape::Square(23) # => false Shape::Square(23) == Shape::Square(99) # => false

All its instances expose (read-only) their respective parameters:

ruby Shape::Square(23).width # => 23

All instances are a kind of Shape:

ruby Shape::Square(23).is_a?(Shape) # => true

And finally, our constructors can have their own special methods, just like we defined area on Circle:

ruby Shape::Circle(1).area # => 3.141592653589793

Installation

Add this line to your application’s Gemfile:

ruby gem 'adts'

And then execute:

$ bundle

Or install it yourself as:

$ gem install adts

Who’s this

This was made by Josep M. Bach (Txus) under the MIT license. I am @txustice on twitter (where you should probably follow me!).