class Regexp::Parser

def quantifier(token)
  offset = -1
  target_node = node.expressions[offset]
  while target_node.is_a?(FreeSpace)
    target_node = node.expressions[offset -= 1]
  end
  target_node || raise(ArgumentError, 'No valid target found for '\
                                      "'#{token.text}' ")
  case token.token
  when :zero_or_one
    target_node.quantify(:zero_or_one, token.text, 0, 1, :greedy)
  when :zero_or_one_reluctant
    target_node.quantify(:zero_or_one, token.text, 0, 1, :reluctant)
  when :zero_or_one_possessive
    target_node.quantify(:zero_or_one, token.text, 0, 1, :possessive)
  when :zero_or_more
    target_node.quantify(:zero_or_more, token.text, 0, -1, :greedy)
  when :zero_or_more_reluctant
    target_node.quantify(:zero_or_more, token.text, 0, -1, :reluctant)
  when :zero_or_more_possessive
    target_node.quantify(:zero_or_more, token.text, 0, -1, :possessive)
  when :one_or_more
    target_node.quantify(:one_or_more, token.text, 1, -1, :greedy)
  when :one_or_more_reluctant
    target_node.quantify(:one_or_more, token.text, 1, -1, :reluctant)
  when :one_or_more_possessive
    target_node.quantify(:one_or_more, token.text, 1, -1, :possessive)
  when :interval
    interval(target_node, token)
  else
    raise UnknownTokenError.new('Quantifier', token)
  end
end