h1. PatternMatching module

h1. → 'patternmatching'

h2. What

Provides a pure ruby module that:
* can build structured objects easily
* can enable pattern match of objects
* can define method as a partial function style

h2. Installing

<pre syntax="ruby">sudo gem install patternmatching</pre>

h2. The basics

This module provides methods for tree pattern matching features.

* For detail, see Wikipedia: "Pattern matching":http://en.wikipedia.org/wiki/Pattern_matching
* Syntax based on meta-programming, like "rspec", and so on.

Note: Default equivalence used in structured pattern matching is 
based on "pattern === data", so "foo(Numeric)" matches with "foo(100)"

Note: Not thread safe now.

h2. Demonstration of usage

<h3>Pattern matching expression</h3>
<pre>
require "patternmatching"

# For DSL style code, include PatternMatching
include PatternMatching

# match example
def calc(code)
  make(code) {
    seems as {plus(:x, :y)} do calc(x) + calc(y) end
    seems as {mul(:x, :y)} do  calc(x) * calc(y) end
    seems something do code end
  }
end

code = build {plus(mul(100, 100), 200)}
p calc(code) #=> 10200
</pre>

<h3>Partial style method</h3>
<pre>
require "patternmatching"

# Structured data builder
code = PatternMatching.build {plus(mul(100, 100), 200)}

# Partial style method example
class Calc
  # At first, extends with the module
  extend PatternMatching

  # def calcm(o), as 3 partial styles
  func(:calcm).seems as {plus(:x, :y)} do
    calcm(x) + calcm(y)
  end
  func(:calcm).seems as {mul(:x, :y)} do
    calcm(x) * calcm(y)
  end
  func(:calcm).seems as {:value} do
    value
  end
end

# use as standard method
p Calc.new.calcm(code) #=> 10200
</pre>

<h3>Array/Enumerable pattern</h3>
<pre>
require "patternmatching"

include PatternMatching

# Example for matching Enumerable
is = build { exact([1,2,3,4,5]) }
make is do
   # _!  matches rest of lists
  seems as {exact([:a,:b, _!(:c)])} do
    puts a.to_s + ", " + b.to_s  + " and " + c.to_s
  end
  seems something do
    puts "not matched"
  end
end # => "1, 2, and 345"
</pre>

<h3>Hash pattern</h3>
<pre>
require "patternmatching"

include PatternMatching

# Example for matching Hash
dict = build { {:name => "Taro", :age => 5} }
make dict do
  seems as {{:name => :name}} do
    puts "He is " + name
  end
  seems something do
    puts "no name"
  end
end # => "He is Taro"
</pre>

<h3>Non-Hash/Object pattern</h3>
<pre>
require "patternmatching"

include PatternMatching

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end
  attr :name
  attr :age
end

# Example for matching Object except Hash
person = Person.new("Jiro", 3)
make person do
  seems as {{:name => :name}} do
    puts "He is " + name
  end
  seems something do
    puts "no name"
  end
end # => "He is Jiro"
</pre>

h2. Forum


h2. How to submit patches

Read the "8 steps for fixing other people's code":http://drnicwilliams.com/2007/06/01/8-steps-for-fixing-other-peoples-code/ and for section "8b: Submit patch to Google Groups":http://drnicwilliams.com/2007/06/01/8-steps-for-fixing-other-peoples-code/#8b-google-groups, use the Google Group above.

The trunk repository is <code>svn://rubyforge.org/var/svn/patternmatching/trunk</code> for anonymous access.

h2. License

This code is free to use under the terms of the MIT license. 

h2. Link

* "Web Site":http://patternmatching.rubyforge.org/
* "Project Page":http://rubyforge.org/projects/patternmatching/

h2. Contact

Comments are welcome. Send an email to "ICHIYAMA Ryoichi":mailto:bellbind@gmail.com. "My blog":http://d.hatena.ne.jp/bellbind (written in Japanese) could be help you.