From: makoto kuwata <kwa@...>
Date: 2007-11-05T11:05:37+09:00
Subject: 30 lines implementation of eRuby

Hi all,

Do you like eRuby? Do you want to customize ERB?

The following is 30 lines implementation of eRuby.
This will help you to get your own eRuby implementation.

    class TinyEruby

      def initialize(input=nil)
        @src = convert(input) if input
      end

      attr_reader :src

      def convert(input)
        src = "_buf = '';"       # preamble
        input.scan(/(.*?)<%(=)?(.*?)%>/m) do |text, ch, code|
          src << " _buf << '#{escape_text(text)}';" unless text.empty?
          src << (ch == '=' ? " _buf << (#{code}).to_s" : code) << ';'
        end
        rest = $' || input
        src << " _buf << '#{escape_text(rest)}';" unless rest.empty?
        src << "\n_buf.to_s\n"   # postamble
        return src
      end

      def escape_text(text)
        return text.gsub!(/['\\]/, '\\\\\&') || text
      end

      def result(_binding=TOPLEVEL_BINDING)
        eval @src, _binding
      end

    end

Usage of TinyEruby is the same as ERB.

The above code may be slow in some cases, because long pattern
matching ('(.*?)' and $1) in convert() is not fast.
You can improve performance of TinyEruby to avoid long matching.

     ...
      def convert(input)
        src = "_buf = '';"       # preamble
        pos = 0
        input.scan(/<%(=)?(.*?)%>/m) do |ch, code|
          match = Regexp.last_match
          len   = match.begin(0) - pos
          text  = input[pos, len]
          pos   = match.end(0)
          src << " _buf << '#{escape_text(text)}';" unless text.empty?
          src << (ch == '=' ? " _buf << (#{code}).to_s" : code) << ';'
        end
        rest = $' || input
        src << " _buf << '#{escape_text(rest)}';" unless rest.empty?
        src << "\n_buf.to_s\n"   # postamble
        return src
      end
      ...

These codes are released in public domain. You can use it freely.
See
http://www.kuwata-lab.com/support/2007/10/09/30-lines-implementation-of-eruby/
for details.

--
regards,
kwatch