gistfile1.scala

scala> val hmm: Option[String] = Some("lala")
scala> hmm collect {{
     |   case rawr if rawr == "lala" => rawr * 2
     | }: PartialFunction[String, String]}
res2: Option[String] = Some(lalalala)

scala> res2 ++ List("teehee")
res3: Iterable[String] = List(lalalala, teehee)

scala> hmm collect {{
     |   case rawr if rawr == "lala" => rawr * 2
     | }: PartialFunction[String, String]} ++ List("teehee")
<console>:11: error: value ++ is not a member of PartialFunction[String,String]
              }: PartialFunction[String, String]} ++ List("teehee")