Ruby internals

flatten.rb

# an imitation of ruby's flatten which takes in a 2nd argument
def flatten(array, n=nil)
  n = -1 if !n
  while n != 0
    is_flat = true
    array = array.inject([]) do |acc, x|
      if x.is_a?(Array)
        is_flat = false
        acc + x
      else
        acc + [x]
      end
    end
    n -= 1 if n
    return array if is_flat
  end
  return array
end