You can also optimize non-recursive tail calls:

  def add10(y: int) -> int:
      return y+10

  def def add11(x: int) -> int:
      # won't get optimized
      return add10(x)+1

  def add11_tail(x: int) -> int:
      # should get optimized
      return add10(x+1)

in `add11_tail` the call to `add10` is in the tail position, i.e. you can "forget" about `add11_tail`'s stack frame since it's not needed anymore. It's still needed in `add10`, because you start in `add11`, call `add10` and go back to to `add11` to add 1 to the result.