class Less::Node::Expression

def _sass_split(arr)
  return arr[0].to_sass_tree, arr[1..-1] unless arr[0] == "("
  parens = 1
  i = arr[1..-1].each_with_index do |e, i|
    parens += 1 if e == "("
    parens -= 1 if e == ")"
    break i if parens == 0
  end
  return _to_sass_tree(arr[1...i+1]), arr[i+2..-1]
end