gistfile1.rbx

require 'rubygems'
require 'spec'
 
# Here is the problem, I want to replace statements like this:
#
# puts (OddRecognizer.new.knows?(1) or OddRecognizer.new.knows?(3)) ? "there are odds" : "there is no odd"
#
# With this syntax:
# puts OddRecognizer.new.knows?(1).or?(3) ? "there are odds" : "there is no odd"
#
# OddRecognizer is just a trivial class just to prove my concept:
class OddRecognizer
  def knows?(value)
    (value % 2) == 0
  end
end
 
describe OddRecognizer do
  before :each do
    @recognizer = OddRecognizer.new
  end
  
  it "should recognize 2" do
    @recognizer.knows?(2).should be_true
  end
  
  it "should not recognize 3" do
    @recognizer.knows?(3).should be_false
  end
end
 
# Here's the implementation
class BooleanEvaluator
 
  Operation = Struct.new :name, :arguments
 
  def initialize(target, method, *args)
    @target, @method = target, method
    @arguments = Array.new << Operation.new(:first, args)
  end
  
  def or?(*args)
    @arguments << Operation.new(:or, args)
    self
  end
  
  def and?(*args)
    @arguments << Operation.new(:and, args)
    self
  end
 
  def true?
    @arguments.inject(false) do |result, operation|
      case operation.name
      when :or then result or @target.send(@method, *operation.arguments)
      when :and then result and @target.send(@method, *operation.arguments)
      else @target.send(@method, *operation.arguments)
      end
    end
  end
  
   def ==(bool)
  	!!true?.equal?(bool)
   end
end
 
# For now let's add a new method that will behave like I want.
class OddRecognizer
  def mknows?(*args)
    BooleanEvaluator.new(self, :knows?, *args)
  end
end
 
# Let's test it.
describe OddRecognizer do
  before :each do
    @recognizer = OddRecognizer.new
  end
  
  it "should return false for 1 or 3 or 5" do
    @recognizer.mknows?(1).or?(3).or?(5).should be_false
  end
  
  it "should return true for 1 or 3 or 6" do
    @recognizer.mknows?(1).or?(3).or?(6).should be_true
  end
  
  # Here lies the problem: in ruby, everything that is not nil nor false evaluates
  # as true in conditional expressions.... Is there any way to modify BooleanEvaluator
  # (or implement it in a different way) to make this work? I don't think so,
  # but maybe there is a way to implement something more close to the thing I want.
  it "should return true for 1 or 3 or 6 without having to call true at the end" do
    # pending "Impossible in ruby?" do
      @recognizer.mknows?(1).or?(3).or?(6).should be_true
    # end
  end
end