“If function” implemented without using existing if-expression

fizzbuzz.rb

# FizzBuzz program.
require 'iffunction'
1.upto(20) do |n|
  _if(n % 15 == 0) {
    puts "FizzBuzz"
  }.elsif(n % 3 == 0) {
    puts "Fizz"
  }.elsif(n % 5 == 0) {
    puts "Buzz"
  }.else {
    puts n
  }
end

iffunction.rb

# iffunction.rb
class NilClass
  def _choose(tval, fval)
    fval
  end
end
class FalseClass
  def _choose(tval, fval)
    fval
  end
end
class Object
  def _choose(tval, fval)
    tval
  end
end
module IfFunc
  Noop = Proc.new {}
  def self._if(cond, blk)
    cond._choose(blk, Noop).call
    cond._choose(Done, Notyet)
  end
  Notyet = Object.new
  class << Notyet
    def elsif(cond, &blk)
      IfFunc._if(cond, blk)
    end
    def else(&blk)
      blk.call
      nil
    end
  end
  Done = Object.new
  class << Done
    def elsif(cond, &blk)
      Done
    end
    def else(&blk)
      nil
    end
  end
end
def _if(cond, &blk)
  IfFunc._if(cond, blk)
end
# EOF