My first version cheats a bit, but passes the tests. Converts the num
to base-5 and back.

def symbolify(num)
  def eval(str)
    str.tr('(?*)-', '01234').to_i(5)
  end
  num.to_s(5).tr('01234', '(?*)-')
end


My second solution cheats badly, failing the delayed eval test. Still,
it's a single line of length 42.  :)

def symbolify(num)
  def eval(str) $num end; $num = num; "()"
end


I need to finish my non-cheating version...