pretty

# File actionpack/lib/action_controller/vendor/rack-1.0/rack/showexceptions.rb, line 33
    def pretty(env, exception)
      req = Rack::Request.new(env)
      path = (req.script_name + req.path_info).squeeze("/")

      frames = exception.backtrace.map { |line|
        frame = OpenStruct.new
        if line =~ /(.*?):(\d+)(:in `(.*)')?/
          frame.filename = $1
          frame.lineno = $2.to_i
          frame.function = $4

          begin
            lineno = frame.lineno-1
            lines = ::File.readlines(frame.filename)
            frame.pre_context_lineno = [lineno-CONTEXT, 0].max
            frame.pre_context = lines[frame.pre_context_lineno...lineno]
            frame.context_line = lines[lineno].chomp
            frame.post_context_lineno = [lineno+CONTEXT, lines.size].min
            frame.post_context = lines[lineno+1..frame.post_context_lineno]
          rescue
          end

          frame
        else
          nil
        end
      }.compact

      env["rack.errors"].puts "#{exception.class}: #{exception.message}"
      env["rack.errors"].puts exception.backtrace.map { |l| "\t" + l }
      env["rack.errors"].flush

      [@template.result(binding)]
    end