A simple implementation of the flatten method

flatten.rb

# Turn arbitrarily nested arrays into a flat one.
# Example: [[1,2,[3]],4] -> [1,2,3,4]

def flatten(array)
  result = []

  array.each do |element|
    if element.is_a?(Array)
      result.concat(flatten(element))
    else
      result << element
    end
  end

  result
end

p flatten([[1,2,[3]],4, [5,6,[7],[8,9]],10])