gistfile1.scala

  val username: Option[String] \/ String = for {
    parsed <- requestJson.parse.swapped(_.map(_.some))           // Parse the JSON.
    jsonObject <- parsed.obj.toRight[Option[String]]             // Get the JSON as a JsonObject instance.
    userIDJson <- jsonObject("userid").toRight[Option[String]]   // Get the "userid" field from the JsonObject.
    userID <- userIDJson.string.toRight[Option[String]]          // Get the value of the "userid" field.
    user <- lookupUser(userID).toRight[Option[String]]           // Get an instance of User for the user ID.
  } yield user.username