Interpreter Pattern

#!/usr/local/bin/ruby
# -*- encoding:utf-8 -*-
require "find"

class Expression
  def |(other)
    Or.new(self, other)
  end
 
  def &(other)
    And.new(self, other)
  end
end

class All < Expression
  def evaluate(dir)
    results = []
    Find.find(dir) do |p|
      next unless File.file?(p)
      results << p
    end
    results
  end
 
end

class FileName < Expression
  def initialize(pattern)
    @pattern = pattern
  end
 
  def evaluate(dir)
    results = []
    Find.find(dir) do |p|
      next unless File.file?(p)
      name = File.basename(p)
      results << p if File.fnmatch(@pattern, name)
    end
    results
  end
end

class Not < Expression
  def initialize(expression)
    @expression = expression
  end
 
  def evaluate(dir)
    All.new.evaluate(dir) - @expression.evaluate(dir)
  end
end

class Or < Expression
  def initialize(expression1, expression2)
    @expression1, @expression2 = expression1, expression2
  end
 
  def evaluate(dir)
    result1 =@expression1.evaluate(dir)
    result2 =@expression2.evaluate(dir)
    (result1 + result2).sort.uniq
  end
end

class Bigger < Expression
  def initialize(size)
    @size = size
  end
 
  def evaluate(dir)
    results = []
    Find.find(dir) do |p|
      next unless File.file?(p)
      name = File.basename(p)
      results << p if File.size(p) > @size
    end
    results
  end
end

class Writable < Expression
  def evaluate(dir)
    results = []
    Find.find(dir) do |p|
      next unless File.file?(p)
      name = File.basename(p)
      results << p if File.writable?(p)
    end
    results
  end
 
end

class And < Expression
  def initialize(expression1, expression2)
    @expression1, @expression2 = expression1, expression2
  end
 
  def evaluate(dir)
    result1 =@expression1.evaluate(dir)
    result2 =@expression2.evaluate(dir)
    (result1 & result2)
  end
end

def all
  All.new
end
def bigger(size)
  Bigger.new(size)
end
def file_name(pattern)
  FileName.new(pattern)
end
def except(expression)
  Not.new(expression)
end
def writable
  Writable.new
end

p ((bigger(1000) & except(writable)) | file_name('*.mp3')).evaluate('/Users/keyes/Desktop/')