txus/adts

Algebraic Data Types for Ruby

ADTs

Algebraic Data Types for Ruby.

Usage

Let's define a Shape data type:

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:

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

What about a square?

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

Our type constructors are even type-checked:

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

Our ADT implements equality by type and value:

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:

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

All instances are a kind of Shape:

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

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

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

Installation

Add this line to your application's Gemfile:

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!).