import org.scalactic._
import org.scalactic.Accumulation._

trait Error
type Errors = Every[Error]
case object AnError extends Error

object ValidationImplicits {

  implicit class ValidationOps[E](val validLeft: Validation[Every[E]]) extends AnyVal {
    def or(validRight: Validation[Every[E]]): Validation[Every[E]] = {
      (validLeft, validRight) match {
        case (Pass, Pass) => Pass
        case (Fail(_), Pass) => Pass
        case (Pass, Fail(_)) => Pass
        case (Fail(errorsLeft), Fail(errorsRight)) => Fail(errorsLeft ++ errorsRight)
      }
    }
  }

}

import ValidationImplicits._

def validate1(s: String): Validation[Errors] = Pass
def validate2(s: String): Validation[Errors] = Fail(One(AnError))
def sOrError = Good("foo")

// Usage:
for {
  s <- sOrError
  if validate1(s) or validate2(s)
} yield s