def prompt(prompt, ltype, indent, line_no)
      p = prompt.dup
      p.gsub!(/%([0-9]+)?([a-zA-Z])/) do
  case $2
  when "N"
    @context.irb_name
  when "m"
    @context.main.to_s
  when "M"
    @context.main.inspect
  when "l"
    ltype
  when "i"
    if $1 
      format("%" + $1 + "d", indent)
    else
      indent.to_s
    end
  when "n"
    if $1 
      format("%" + $1 + "d", line_no)
    else
      line_no.to_s
    end
  when "%"
    "%"
  end
      end
      p
    end