class Syntax::YAML

def step
  if bol?
    case
      when scan(/---(\s*.+)?$/)
        start_group :document, matched
      when scan(/(\s*)([a-zA-Z][-\w]*)(\s*):/)
        start_group :normal, subgroup(1)
        start_group :key, subgroup(2)
        start_group :normal, subgroup(3)
        start_group :punct, ":"
      when scan(/(\s*)-/)
        start_group :normal, subgroup(1)
        start_group :punct, "-"
      when scan(/\s*$/)
        start_group :normal, matched
      when scan(/#.*$/)
        start_group :comment, matched
      else
        append getch
    end
  else
    case
      when scan(/[\n\r]+/)
        start_group :normal, matched
      when scan(/[ \t]+/)
        start_group :normal, matched
      when scan(/!+(.*?^)?\S+/)
        start_group :type, matched
      when scan(/&\S+/)
        start_group :anchor, matched
      when scan(/\*\S+/)
        start_group :ref, matched
      when scan(/\d\d:\d\d:\d\d/)
        start_group :time, matched
      when scan(/\d\d\d\d-\d\d-\d\d\s\d\d:\d\d:\d\d(\.\d+)? [-+]\d\d:\d\d/)
        start_group :date, matched
      when scan(/['"]/)
        start_group :punct, matched
        scan_string matched
      when scan(/:\w+/)
        start_group :symbol, matched
      when scan(/[:]/)
        start_group :punct, matched
      when scan(/#.*$/)
        start_group :comment, matched
      when scan(/>-?/)
        start_group :punct, matched
        start_group :normal, scan(/.*$/)
        append getch until eos? || bol?
        return if eos?
        indent = check(/ */)
        start_group :string
        loop do
          break if eos?
          line = check_until(/[\n\r]|\Z/)
          break if line.nil?
          if line.chomp.length > 0
            this_indent = line.chomp.match( /^\s*/ )[0]
            break if this_indent.length < indent.length
          end
          append scan_until(/[\n\r]|\Z/)
        end
      else
        start_group :normal, scan_until(/(?=$|#)/)
    end
  end
end