tpl.rb

# -*- coding: utf-8 -*-

module Tpl
  def self.new(template, variables = [], output_method = :concat)
    template = template.dup
    m = Module.new
    start = template.index("<%")

    render_definition = ["def self.render(__v = {}, __o = '');"]
    render_definition += variables.map{|v| "#{v} = __v[:#{v}];"}
    compile(template, output_method, render_definition)
    render_definition << "__o; end"
    m.module_eval render_definition.join

    m
  end

  def self.compile(template, output_method, render_definition)
    i = 0
    len = template.length

    until i == len
      start = template.index("<%", i)

      unless start
        render_definition << "__o.#{output_method}(#{template[i..len].inspect});"
        return
      end

      render_definition << "__o.#{output_method}(#{template[i...start].inspect});"

      stop = template.index("%>", start)
      i = stop + 2

      case template[start + 2]
      when "=" then
        render_definition << "__r = (#{template[start+3..stop-1]}).to_s; __o.#{output_method}(__r);"
      when "#" then
        # ignore, # is a comment
      else
        render_definition << "#{template[start+3..stop-1]};"
      end
    end
  end
end

tpl = Tpl.new("The sum is <%=2+2%> Also substitute <%=myfield%> ok", %w(myfield))
puts tpl.render({:myfield => 10})
tpl2 = Tpl.new("ñañaña")
puts tpl2.render
tpl3 = Tpl.new("Testing loops: <% 3.times do %> * <% end %>")
puts tpl3.render