Either ops to accumumate errors (and symmetric right method)

EitherOps.scala

import scala.util._

implicit class EitherLeftOps[L](eithers: Seq[Either[L,_]]){
  def collectLefts: Seq[L] = eithers.collect { 
    case Left(l) => l
  }
}

implicit class EitherRightOps[R](eithers: Seq[Either[_,R]]){
  def collectRights: Seq[R] = eithers.collect { 
    case Right(r) => r
  }
}

sealed trait Error
case class NumericError(message: String) extends Error
case class OtherError(message: String) extends Error

val e1 = Right(1)
val e2 = Left(NumericError("nan"))
val e3 = Left(OtherError("foo"))

val errors = Seq(e1,e2,e3).collectLefts