for comprehension error handling

either.scala

val aOpt: Option[Int] = Some(1)
  
val c = for {
  a <- aOpt.toRight("Missing something in first level!").right
  b <- Option(2).toRight("Another failure!").right
} yield {
  a + b
}

def onSuccess(i: Int) = i
def onFailure(message: String) = throw new Exception(message)
val r = c.fold(onFailure, onSuccess)