Ruby with Logic, a prolog-style logic programming system for Ruby
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README.rdoc

rulog

github.com/jimwise/rulog

Author

Jim Wise (jwise@draga.com)

Copyright

Copyright © 2011 Jim Wise

License

2-clause BSD-Style (see LICENSE.txt)

DESCRIPTION:

Rulog is Ruby with Logic, a Logic Programming system for Ruby.

Rulog follows Prolog conventions where possible to do so within a Ruby DSL, but makes a strong effort to retain a Rubyish “feel” wherever possible. The underlying functionality of Rulog, including the unification engine and solver are also exposed directly through a set of Ruby classes.

While usable, this is a work in progress – what's here now is a working Logic Programming environment for Ruby, with integration with Ruby language features (including unification of Prolog-style functors and Ruby scalar and Enumerable types), along with a DSL to make these easier to use. This is sufficient for writing pure logic programs in Ruby, or for adding logic-programming-based capabilities to a Ruby program.

Future releases will tighten the integration between this logic engine and the rest of Ruby, including adding:

  • the ability to escape to a Ruby block during unification, much as the “is” operator in Prolog allows direct use of mathematical operations at unification time

  • the ability to include a predicate written in Ruby in a Rulog rule, similar to the use of FFI systems in modern prolog environments

  • further improvements to the DSL used with Rulog::declare, to simplify use of these and other Rulog features

The implementation of prolog's cut operator (!) is also not quite right at this point – while cut should commit only to all choices back to the choice of the rule containing the cut, Rulog's cut! DSL operator currently commits to all choices made to this point in the decision tree. This will be fixed in a future version (support for this is already present in ambit).

REQUIREMENTS:

Rulog depends on the ambit gem for backtracking. Given this, Rulog will not work in JRuby or MacRuby (no callcc). It is tested, and should work in Ruby 1.9.3 and 1.8.7.

INSTALL:

To install:

$ gem install rulog

DEVELOPERS:

After checking out the source, run:

$ rake newb

This task will install any missing dependencies, run the tests/specs, and generate the RDoc.

SYNOPSIS:

What is Logic Programming?

Logic programming is a form of programming which consists of stating a series of rules which describe

How to Use This Gem

To get started, include this gem using

require 'rubygems'
require 'rulog'

This gem provides the Rulog module. This module provides several methods which allow use of Logic Programming with Ruby.

A DSL for Facts and Rules

man(:abraham)
man(:isaac)
man(:jacob)

woman(:sarah)
woman(:rebekah)
woman(:rachel)

parent(:abraham, :isaac)
parent(:sarah, :isaac)
parent(:isaac, :jacob)
parent(:rebekah, :jacob)

father(v(:x), v(:y)) [ parent(v(:x), v(:y)), man(:x) ]
son(v(:x), v(:y)) [ parent(v(:x), v(:y)), man(:y) ]

Declaring Facts and Rules

Querying for a Solution

More Than One Answer

Cutting

Limitations of the current cut implementation

Longer example

References

1

Sterling, Leon and Ehud Shapiro, The Art of Prolog, MIT Press, 1994

LICENSE:

(The BSD 2-clause License)

Copyright (c) 2011 Jim Wise
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.