scala3-Underscores-Fors.scala

case class User(name: String, password: String)

def checkName(user: User): Either[String,User] = 
  if (user.name.isEmpty) Left("Empty name") 
  else Right(user)

def checkPassword(user: User): Either[String,User] = 
  if (user.password.length < 8) Left("Password needs 8+ characters") 
  else Right(user)

Seq(User("", "12345678"), User("Dean", "1234"), User("Dean", "12345678")).map {
  user => for {
    _ <- checkName(user)
    u <- checkPassword(user)
  } yield u
}  // List(Left(Empty name), Left(Password needs 8+ characters), Right(User(Dean,12345678)))