Cats IO-在flatmap内进行尾部递归调用

我试图使返回IO尾部的函数递归,但它不编译,因为我在flatMap中使用它。我知道有些东西是为这个目的而构建的,比如tailRec,但我正在寻找一些关于如何使用它们的指导。下面是示例代码。

    import cats.effect.IO
    import scala.annotation.tailrec

    def process(since: Option[String]): IO[Seq[String]] = {

      @tailrec
      def go(startIndex: Int): IO[(Int, Seq[String])] = {

        val program = since match {
          case Some(s) =>
            for {
              r <- fetchResponse(s, startIndex)
              size = r.size
              ss = r.data
              _ <- writeResponse(ss)

            } yield (size,  r)
          case None => IO((0, Seq.empty[String]))
        }

        program.flatMap { case (size, _) =>
          if (startIndex <= size) go( startIndex + size)
          else IO((0, Seq.empty))
        }
      }

      go(0).map(o => o._2)
    }

    case class Response(size: Int, data: Seq[String])

    def fetchResponse(s: String, i: Int): IO[Response] = ???

    def writeResponse(r: Seq[String]): IO[Int] = ???