B001e

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

.. admonition

Abstract

B001e_ is a message-sending based re-implementation of the Boolean operators “and“, “or“ and “not“ and the Boolean expressions “if“ and “unless“ in pure Ruby. Lazy Evaluation / Short-circuiting is achieved through the use of blocks and lambda expressions.

.. _B001e: JoergWMittag.GitHub.Com/b001e/

.. contents

What

This library contains sample re-implementations of the Boolean operators “and“, “or“ and “not“ and the Boolean expressions “if“ and “unless“, 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 c1 && c2 t elsif c3 ei else e end

becomes

c1.and { c2 }.ifelse ->{ t }, ->{ c3.ifelse ->{ ei }, ->{ e } }

.. _Smalltalk: 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 “and“ and “or“ are still builtin operators and “if“ and “unless“ still builtin keywords.

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: Ruby-Forum.Com/forum/4/ .. _Ruby-Core: 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.

Where

At ‘GitHub <GitHub.Com/JoergWMittag/B001e/>`_, of course!

Installation

gem install b001e

Usage

require ‘b001e’

true.and { nil.or { 42 } }.if { puts “It’s true!” } # Equivalent to: if true && (nil || 42) then puts “It’s true!” end

false.ifelse ->{ puts “You’ll never see this.” }, ->{ puts ‘But this!’ } # Equivalent to: if false then puts “You’ll never see this.” else puts ‘But this!’ end

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: 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: GitHub.Com/JoergWMittag/B001e/tree/master/LICENSE.txt .. _RubySpec license: GitHub.Com/RubySpec/RubySpec/tree/master/LICENSE