Ruby is a great example of multi-paradigm programming language: it allows you to write code in object-oriented, imperative or functional styles. Ruby have much in common with functional programming languages: high-order functions, closures, anonymous functions, continuations, statements all values. If you want to use more functional programming patterns and tools, you might want to take a look on Functional Ruby gem.

Features

• Thread-safe, immutable data structures
• Protocol specifications
• Functions overloading
• Either, Option classes
• Immutable variation of Ruby’s OpenStruct class
• Memoization
• Lazy execution
• Tuples
• Pattern matching

Installing

Install this gem with or without bundler:

1gem install functional-ruby
2#  gem 'functional-ruby'

And then require it in your project:

#+begin_src ruby require ‘functional’ #+end_src

Immutable data structures

#+begin_src ruby Address = Functional::Record.new(:city, :country, :street, :house) do mandatory :country, :city default :city, ‘Moscow’ default :country, ‘Russia’ end # <record Address :city=>“Moscow”, :country=>“Russia”, :street=>nil, :house=>nil> #+end_src

Immutable OpenStruct

Immutable, thread-safe, write-once and read-only object variation of OpenStruct:

#+begin_src ruby name = Functional::ValueStruct.new firstname: ‘Hodor’, lastname: ‘Hodor’ name.get :firstname # Hodor name.lastname # Hodor name.firstname? # true #+end_src

Tuples

Tuple is a data structure that is similar to array, but is immutable and has a fixed length.

#+begin_src ruby tuple = Functional::Tuple.new %w(one two three) tuple.at 0 # one tuple.last 0 # three tuple.fetch 4, ‘four’ # four tuple.tail.to_a # [’two’, ’three’] tuple.repeat(2).to_a.join ‘,’ # one, two, three, one, two, three #+end_src

Protocols

Protocols are specifications to provide polymorphism and method-dispatch mechanism with strong typing, inspired by Clojure protocols:

#+begin_src ruby Functional::SpecifyProtocol(:Address) do attr_accessor :city attr_accessor :country attr_accessor :street attr_accessor :house end #+end_src

Pattern matching

#+begin_src ruby

class AddressChecker include Functional::PatternMatching include Functional::Protocol include Functional::TypeCheck

def msg ‘You live in Moscow, Russia’ end

defn(:msg, _) do |addr| “You live in #{addr}” end

defn(:msg, _) { |addr| “You live in #{addr.house}, #{addr.street}, #{addr.city}, #{addr.country}” } .when { |addr| Satisfy?(addr, :Address) }

defn(:msg, :name, _) do |addr| “Somebody live in #{addr}” end

defn(:msg, _) { |zip| “Your zip is #{zip}” }.when { |addr| Type?(addr, Fixnum) } end #+end_src

Conclusion

If you like functional programming, and want to use it’s patterns and tools with Ruby, then you can use Functional Ruby gem to write code in more functional style. You can find more information in API documentation.