comp

A Ruby library to add function composition to Procs (including lambdas) and Methods.

Current version: 1.0.0
Supported Ruby versions: 1.9.2, 1.9.3, 2.0, 2.1, 2.2

Installation

gem install comp -v '~> 1.0'

Or, in your Gemfile:

gem 'comp', '~> 1.0'

Usage

require 'comp'

# Basic usage
add = proc { |x, y| x + y }
double = proc { |x| x * 2 }
double_after_add = double * add

double_after_add.call(1, 2)
#=> 6

# Composing Procs and other callables
class Parser
  def call(json)
    JSON.load(json)
  end
end

extract_name = proc { |attributes| attributes.fetch('name') }
(extract_name * Parser.new).call('{"name": "Alice"}')
#=> "Alice"

Requiring comp will require two files:

• comp/proc: add Proc#* if it hasn't already been defined;
• comp/method: add Method#* if it hasn't already been defined.

API Documentation

Proc#*

increment_and_add = proc { |x| x * 2 } * proc { |x| x + 1 }
increment_and_add.call(1)
#=> 4

Composes a Proc (f) with any object that responds to call (g) returning a new Proc which will call g with any given arguments (including blocks) and then call f with the result.

If f was created with lambda, the resulting Proc will also be a lambda.

Method#*

class Number
  def add(x, y)
    x + y
  end

  def double(x)
    x * 2
  end
end

(Number.new.method(:double) * Number.new.method(:add)).call(2, 3)
#=> 10

Composes a Method (f) with any object that responds to call (g) returning a new Proc which will call g with any given arguments (including blocks) and then call f with the result.

Why isn't this in Ruby itself?

Good question: I'd like to change that.

Acknowledgements

• Piotr Solnica's Transproc for initially inspiring me to look into function composition in Ruby;
• Tom Stuart for suggesting that I extract this into a gem.

License

Copyright © 2015 Paul Mucur.

Distributed under the MIT License.