Function to PartialFunction

liftToPF.scala

private def liftToPF[X <: Y, W, Y](f: Function[X, W])(implicit ct: ClassTag[X]): PartialFunction[Y, W] =
  new PartialFunction[Y, W] {
    override def isDefinedAt(x: Y): Boolean = ct.runtimeClass.isInstance(x)
    override def apply(v1: Y): W = f(v1.asInstanceOf[X])
  }

sealed trait MyError
case class ErrorOne(msg: String) extends MyError
case class ErrorTwo(msg: String) extends MyError
case class ErrorThree(msg: String) extends MyError

val errorHandler: MyError => F[Response[F]] = {
  case ErrorOne(msg) => BadRequest(msg)
  case ErrorTwo(msg) => NotFound(msg)
}

// When using recoverWith from ApplicativeError you can get matching exhaustiveness. Eg with Http4s:
users.flatMap(x => Ok(x.asJson)).recoverWith(liftToPF(errorHandler))

// match may not be exhaustive.
// [warn] It would fail on the following input: ErrorThree(_)
// [warn]   val errorHandler: MyError => F[Response[F]] = {
// [warn]                                                  ^
// [warn] one warning found