kleisli-violates-monad-laws.scala

import cats.{Id, MonadError}
import cats.data.Kleisli
import cats.implicits._
import cats.free.FreeT

type F[A] = Kleisli[FreeT[Id, Either[Int, ?], ?], Unit, A]
val F = MonadError[F, Int]

def run[A](fa: F[A]): Either[Int, A] =
  fa.run(()).runM(ft => Right(ft))

def map1[A, B](fa: F[A])(f: A => B): F[B] =
  fa.map(f)

def map2[A, B](fa: F[A])(f: A => B): F[B] =
  fa.flatMap(a => f(a).pure[F])

val eff1 = F.handleErrorWith(map1(F.fromEither(42.asLeft[String]))(_.asRight[Int]))(_.asLeft[String].pure[F])
val eff2 = F.handleErrorWith(map2(F.fromEither(42.asLeft[String]))(_.asRight[Int]))(_.asLeft[String].pure[F])

run(eff1)   // => Right(Left(42))
run(eff2)   // => Left(42)