EitherBench.scala

import cats.data.Xor
import cats.syntax.all._
import org.openjdk.jmh.annotations.{ Benchmark, Scope, State }

@State(Scope.Benchmark)
class EitherBench {
  val ea: Either[String, Int] = Right(1)
  val eb: Either[String, Int] = Right(2)
  val ec: Either[String, Int] = Right(3)

  val xa: Xor[String, Int] = Xor.right(1)
  val xb: Xor[String, Int] = Xor.right(2)
  val xc: Xor[String, Int] = Xor.right(3)

  @Benchmark def flatMapsEither(): Either[String, Int] = {
    import cats.implicits._
    for {
      a <- ea; b <- eb; c <- ec
    } yield a + b + c
  }

  @Benchmark def flatMapsEitherSyntax(): Either[String, Int] = {
    import EitherSyntax._
    for {
      a <- ea; b <- eb; c <- ec
    } yield a + b + c
  }

  @Benchmark def flatMapsXor(): Xor[String, Int] = for {
    a <- xa; b <- xb; c <- xc
  } yield a + b + c

  @Benchmark def cartesianEither(): Either[String, Int] = {
    import cats.implicits._
    (ea |@| eb |@| ec).map(_ + _ + _)
  }

  @Benchmark def cartesianEitherSyntax(): Either[String, Int] = {
    import EitherSyntax._
    for {
      a <- ea; b <- eb; c <- ec
    } yield a + b + c
  }

  @Benchmark def cartesianXor(): Xor[String, Int] = (xa |@| xb |@| xc).map(_ + _ + _)
}

object EitherSyntax {
  implicit class EitherOps[A, B](val self: Either[A, B]) extends AnyVal {
    def map[C](f: B => C) =
      self match {
        case Right(b) => Right(f(b))
        case left @ Left(a) => left.asInstanceOf[Either[A, C]]
      }

    def flatMap[C](f: B => Either[A, C]) =
      self match {
        case Right(b) => f(b)
        case left @ Left(a) => left.asInstanceOf[Either[A, C]]
      }
  }
}

jmh:run with default arguments:

[info] Benchmark                           Mode  Cnt         Score        Error  Units
[info] EitherBench.cartesianEither        thrpt  200  19839997.767 ±  97340.453  ops/s
[info] EitherBench.cartesianEitherSyntax  thrpt  200  70361484.969 ± 336307.506  ops/s
[info] EitherBench.cartesianXor           thrpt  200  26506086.351 ± 106640.262  ops/s
[info] EitherBench.flatMapsEither         thrpt  200  28634233.565 ± 202999.799  ops/s
[info] EitherBench.flatMapsEitherSyntax   thrpt  200  70627088.756 ± 328028.965  ops/s
[info] EitherBench.flatMapsXor            thrpt  200  71494999.826 ± 248440.207  ops/s