erb4html.rb

require 'erb'

class ERB
  class ERBString < String
    def to_s; self; end

    def erb_concat(s)
      if self.class === s
        concat(s)
      else
        concat(erb_quote(s))
      end
    end

    def erb_quote(s); s; end
  end
end

class ERB4Html < ERB
  def self.quoted(s)
    HtmlString.new(s)
  end

  class HtmlString < ERB::ERBString
    def erb_quote(s)
      ERB::Util::html_escape(s)
    end
  end

  def set_eoutvar(compiler, eoutvar = '_erbout')
    compiler.put_cmd = "#{eoutvar}.concat"
    compiler.insert_cmd = "#{eoutvar}.erb_concat"
    compiler.pre_cmd = ["#{eoutvar} = ERB4Html.quoted('')"]
    compiler.post_cmd = [eoutvar]
  end
end

if __FILE__ == $0
  str = '<%= str %>'

  puts str
  erb = ERB4Html.new(str)
  str = erb.result(binding)
  puts str
  puts erb.result(binding)
  str = String.new(str)
  puts erb.result(binding)
end