Mark up plain text lines as HTML lists

lines-to-html-list.rb

def to_list(text)
  ol_prefix = /^\d+\.?\s*/
  dl_prefix = /^(.+):\s*/
  ul_prefix = /^[^\s]+\s*/
  
  lines = text.split("\n").map { |line| line.strip }
  if lines.any?
    tag, pattern = if lines.first =~ ol_prefix
      ['ol', ol_prefix]
    elsif lines.first =~ dl_prefix
      ['dl', dl_prefix]
    else
      ['ul', ul_prefix]
    end
    "<#{tag}>\n%s</#{tag}>" % lines.inject('') do |output, line|
      if pattern == dl_prefix
        output += "\t<dt>%s</dt>\n\t<dd>%s</dd>\n" % [line[pattern, 1], line.gsub(pattern, '')]
      else
        output += "\t<li>%s</li>\n" % line.gsub(pattern, '')
      end
    end
  else
    text
  end
end