if_like_io_language.rb

#!ruby
module Kernel
  def if_true(bool, &block)
    if bool
      block.call
      return true
    else
      return false
    end
  end
  
  def if_false(bool, &block)
    return if_true(!bool, &block)
  end
end

class TrueClass
  def else
    return self
  end
end

class FalseClass
  def else
    yield
    return nil
  end
end

if __FILE__ == $0
  TEST_EXAMPLES = [true, false, nil, "Matz", 1234, 12.00]
  TEST_EXAMPLES.each.each do |x|
    print "#{x.class} #{x.inspect}: "
    
    print "if_true() == "
    if_true(x){ print "true" }.else{ print "false" }
    print ", if_false() == "
    if_false(x){ print "false" }.else{ print "true" }
    print ", if == "
    if x then print "true" else print "false" end
    puts
  end
  puts
  
  require 'test/unit'
  class ExtIfTest < Test::Unit::TestCase
    TEST_EXAMPLES.each do |x|
      define_method "test_if_true_with_#{x}" do
        result = nil; if_true(x){ result = true }.else{ result = false }
        assert(result == (x ? true : false))
      end
      define_method "test_if_false_with_#{x}" do
        result = nil; if_false(x){ result = false }.else{ result = true }
        assert(result == (x ? true : false))
      end
    end
  end
end