JoergWMittag-boole

======= Boole

---

A message-sending based re-implementation of Boolean operators in pure Ruby

.. admonition:: Abstract

Boole_ is a message-sending based re-implementation of the 
Boolean operators ``if``, ``unless``, ``and``, ``or`` and 
``not`` in pure Ruby. Lazy Evaluation / Short-circuiting is 
achieved through the use of blocks and lambda expressions.

.. _Boole: https://JoergWMittag.GitHub.Com/Boole/

.. contents::

What

This library contains sample re-implementations of the Boolean operators if, unless, and, or and not in pure Ruby. The style is heavily inspired by Smalltalk_ and its relatives: the operators become messages that take block parameters and are sent to the conditionals.

Operator / keyword style::

if condition1 && condition2
	then_block
elsif condition3
	elsif_block
else
	else_block
end

becomes::

condition1.and { condition2 }.ifelse ->() { then_block }, ->() { condition3.ifelse ->() { elsif_block }, ->() { else_block } }

.. _Smalltalk: http://Smalltalk.Org/

Why

Every so often, there is a discussion on either the Ruby-Talk_ or Ruby-Core_ mailinglists, whether the number of operators that are not backed by methods should be reduced. In Ruby 1.9, ! and != have already become methods, but if, unless, and and or are still builtin operators.

One argument that is sometimes brought up is that because of the short-circuiting nature of those operators, implementing them as methods is impossible or at least hard. I just wanted to see how hard it really is!

.. _Ruby-Talk: http://Ruby-Forum.Com/forum/4/ .. _Ruby-Core: http://Ruby-Forum.Com/forum/14/

How

All the operators become methods. The logic is achieved through polymorphism: basically, NilClass and FalseClass get one set of implementations, Object gets the opposite set.

Lazy Evaluation is achieved with blocks: if a block is not supposed to be evaluated, it is simply never yield\ ed to.

Installation

::

gem install JoergWMittag-boole

Usage

::

begin require 'rubygems'; rescue LoadError
else begin gem 'JoergWMittag-boole', '~> 0.0.1'; rescue Gem::LoadError; end end
require 'boole'

true.and { nil.or { 42 } }.if { puts "It's true!" }

false.ifelse ->() { puts "You'll never see this." }, ->() { puts 'But this!' }

Acknowledgements

Style

The API style is heavily influenced by Smalltalk_.

Implementation

The implementation is literally textbook: every introductory CS text should have it.

Specs

The Specs were directly lifted from the RubySpec_ project.

.. _RubySpec: http://RubySpec.Org/

License

My original work is licensed under the MIT X11 License_.

.. include:: LICENSE.txt :literal:

The RubySpec license_ is also MIT X11.

.. include:: spec/LICENSE.txt :literal:

.. _MIT X11 License: https://GitHub.Com/JoergWMittag/Boole/tree/master/LICENSE.txt .. _RubySpec license: https://GitHub.Com/RubySpec/RubySpec/tree/master/LICENSE