QuickSilver Scoring method

class String
  def to_score(abbrev)
    return 0.9 if abbrev.empty?
    return 0.0 if length < abbrev.length

    tail = ""
    loop do
      return 0 if abbrev.empty?
      unless md = match(/#{abbrev}/i)
        abbrev, tail = abbrev.split_at(-1)
        next
      else
        remaining_score = md.post_match.to_score(tail)
        return calc_score(md, remaining_score)
      end
    end
  end

  protected
  def calc_score(md, remaining_score)
    if remaining_score.zero?
      0
    else
      score = (1 * md.to_s.length) + (remaining_score * md.post_match.length)
      if md.pre_match =~ /[\s_]+$/
        score += 0.85 * (md.pre_match.length - $&.length) + 1 * $&.length
      elsif !md.pre_match.empty? and md.to_s =~ /^[A-Z]/
        score += 0.85 * md.pre_match.gsub(/[A-Z]/, "").length
      end
      score / self.length
    end
  end

  def split_at(index)
    return slice(0...index), ( slice(index..-1) || "" )
  end
end