aif.rb

class Aif
  def initialize(cond)
    @cond = cond
  end
  
  def else
    yield unless @cond
  end
end

class Object
  def aif(cond)
    yield(cond) if cond
    Aif.new(cond)
  end
end

if $0 == __FILE__
  str = "foo bar"
  aif(/(.+) (.+)/.match(str)) do |it|
    puts "first  element: #{it[1]}"
    puts "second element: #{it[2]}"
  end.else do
    puts "no match"
  end
end