Side-effect free handling of exceptions.The three first expressions can throw something

snippet.scala

  def exp[T](t: => T) =
            (scala.util.control.Exception.allCatch either t).right

  def readJson(dataField:Option[String],json:JsValue):Either[Throwable,JsValue] = {
    for (
      contents <- exp( json.asJsObject.getFields("rsp")(0) );
      stat <- exp( contents.asJsObject.getFields("stat")(0).convertTo[String] );
      jsonObject <- exp (
        dataField match {
          case Some(field) => contents.asJsObject.getFields(field)(0)
          case None => contents
        }
      ) ;
      ret <- Either.cond(
            stat == "ok",
            jsonObject,
            new Exception(contents.toString, None) {}
          ).right
    ) yield (ret)
  }