and example of using fs2 (and some private CSV row typeclass code) to do wordcount.

wordcount.scala

package dev.posco.hiona.jobs

import cats.effect.{Blocker, IOApp, IO, ExitCode}
import dev.posco.hiona._
import java.nio.file.Paths

object WordCountSimple extends IOApp {
  case class Record(key: String, value: Long)

  def run(args: List[String]): IO[ExitCode] =
    Blocker[IO].use { blocker =>
      val path = Paths.get(args(0))
      val stream = Row.csvToStream[IO, Record](path, skipHeader = true, blocker = blocker)

      stream.fold(Map.empty[String, Long]) { case (m, Record(k, v)) =>
        m.get(k) match {
          case Some(v0) => m.updated(k, v0 + v)
          case None => m.updated(k, v)
        }
      }
      .map(_.toString)
      .lines(System.out)
      .compile
      .drain
      .as(ExitCode.Success)
    }
}