Dumb and basic version of pattern matching construct in Ruby

matching.rb

class Array
  def extract_options!
    last.is_a?(::Hash) ? pop : {}
  end
end

def match(*args)
  rules = args.extract_options!
  if rules.has_key?(*args)
    rules[*args].call 
  else 
    rules[:default].call(*args)
  end
end

def fibonacci x
  match x, 
    0  => ->{0},
    1  => ->{1},
    :default => ->(n){fibonacci(n-1) + fibonacci(n-2)}
end

puts fibonacci(20)