README.md
# Functional Ruby
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**A gem for adding functional programming tools to Ruby. Inspired by [Erlang](http://www.erlang.org/),
[Clojure](http://clojure.org/), and [Functional Java](http://functionaljava.org/).**
## Introduction
Two things I love are [Ruby](http://www.ruby-lang.org/en/) and
[functional](https://en.wikipedia.org/wiki/Functional_programming)
[programming](http://c2.com/cgi/wiki?FunctionalProgramming).
If you combine Ruby's ability to create functions sans-classes with the power
of blocks, `proc`, and `lambda`, Ruby code can follow just about every modern functional
programming design paradigm. Add to this Ruby's vast metaprogramming capabilities
and Ruby is easily one of the most powerful languages in common use today.
### Goals
Our goal is to implement various functional programming patterns in Ruby. Specifically:
* Be an 'unopinionated' toolbox that provides useful utilities without debating which is better or why
* Remain free of external gem dependencies
* Stay true to the spirit of the languages providing inspiration
* But implement in a way that makes sense for Ruby
* Keep the semantics as idiomatic Ruby as possible
* Support features that make sense in Ruby
* Exclude features that don't make sense in Ruby
* Keep everything small
* Be as fast as reasonably possible
## Features
The primary site for documentation is the automatically generated [API documentation](http://jdantonio.github.io/functional-ruby/).
* Protocol specifications inspired by Clojure [protocol](http://clojure.org/protocols),
Erlang [behavior](http://www.erlang.org/doc/design_principles/des_princ.html#id60128),
and Objective-C [protocol](https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithProtocols/WorkingwithProtocols.html).
* Function overloading with Erlang-style [function](http://erlang.org/doc/reference_manual/functions.html)
[pattern matching](http://erlang.org/doc/reference_manual/patterns.html).
* Simple, thread safe, immutable data structures, such as `Record`, `Union`, and `Tuple`, inspired by
[Clojure](http://clojure.org/datatypes), [Erlang](http://www.erlang.org/doc/reference_manual/records.html),
and other functional languages.
* Thread safe, immutable `Either` and `Option` classes based on [Functional Java](http://functionaljava.org/) and [Haskell](https://hackage.haskell.org/package/base-4.2.0.1/docs/Data-Either.html).
* [Memoization](http://en.wikipedia.org/wiki/Memoization) of class methods based on Clojure [memoize](http://clojuredocs.org/clojure_core/clojure.core/memoize).
* Lazy execution with a `Delay` class based on Clojure [delay](http://clojuredocs.org/clojure_core/clojure.core/delay).
* `ValueStruct`, a simple, thread safe, immutable variation of Ruby's [OpenStruct](http://ruby-doc.org/stdlib-2.0/libdoc/ostruct/rdoc/OpenStruct.html) class.
* Thread safe data structures, such as `FinalStruct` and `FinalVar`, which can be written to at most once
before becoming immutable. Based on [Java's `final` keyword](http://en.wikipedia.org/wiki/Final_(Java)).
### Supported Ruby Versions
MRI 2.0 and higher, JRuby (1.9 mode), and Rubinius 2.x. This library is pure Ruby and has no gem dependencies.
It should be fully compatible with any interpreter that is compliant with Ruby 2.0 or newer.
### Install
```shell
gem install functional-ruby
```
or add the following line to Gemfile:
```ruby
gem 'functional-ruby'
```
and run `bundle install` from your shell.
Once you've installed the gem you must `require` it in your project:
```ruby
require 'functional'
```
## Examples
Specifying a [protocol](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Protocol):
```ruby
Functional::SpecifyProtocol(:Name) do
attr_accessor :first
attr_accessor :middle
attr_accessor :last
attr_accessor :suffix
end
```
Defining immutable [data structures](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/AbstractStruct) including
[Either](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Either),
[Option](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Option),
[Union](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Union) and
[Record](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Record)
```ruby
Name = Functional::Record.new(:first, :middle, :last, :suffix) do
mandatory :first, :last
default :first, 'J.'
default :last, 'Doe'
end
anon = Name.new #=> #<record Name :first=>"J.", :middle=>nil, :last=>"Doe", :suffix=>nil>
matz = Name.new(first: 'Yukihiro', last: 'Matsumoto') #=> #<record Name :first=>"Yukihiro", :middle=>nil, :last=>"Matsumoto", :suffix=>nil>
```
[Pattern matching](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/PatternMatching)
using [protocols](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Protocol),
[type](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/TypeCheck) checking,
and other options:
```ruby
class Foo
include Functional::PatternMatching
include Functional::Protocol
include Functional::TypeCheck
def greet
return 'Hello, World!'
end
defn(:greet, _) do |name|
"Hello, #{name}!"
end
defn(:greet, _) { |name|
"Pleased to meet you, #{name.full_name}!"
}.when {|name| Type?(name, CustomerModel, ClientModel) }
defn(:greet, _) { |name|
"Hello, #{name.first} #{name.last}!"
}.when {|name| Satisfy?(name, :Name) }
defn(:greet, :doctor, _) { |name|
"Hello, Dr. #{name}!"
}
defn(:greet, nil, _) { |name|
"Goodbye, #{name}!"
}
defn(:greet, _, _) { |_, name|
"Hello, #{name}!"
}
end
```
Performance improvement of idempotent functions through [memoization](http://rubydoc.info/github/jdantonio/functional-ruby/master/Functional/Memo):
```ruby
class Factors
include Functional::Memo
def self.sum_of(number)
of(number).reduce(:+)
end
def self.of(number)
(1..number).select {|i| factor?(number, i)}
end
def self.factor?(number, potential)
number % potential == 0
end
memoize(:sum_of)
memoize(:of)
end
```
## Contributing
1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new Pull Request
## License and Copyright
*Functional Ruby* is free software released under the [MIT License](http://www.opensource.org/licenses/MIT).