gistfile1.scala

class RelTriple(subj:String,pred:String,obj:String)

object RelTriple {
    def fromJson(j:Any):Option[RelTriple] = {
        return j match {
            case m:Map[String,Any] =>
                // FIXME: how do I avoid all those coercions
                // or somehow move theme to a better place?
               (m get "subject")   flatMap ((s:Any) =>
               (m get "object")    flatMap ((o:Any) =>
               (m get "predicate") flatMap ((p:Any) =>
                   Some(new RelTriple(s.asInstanceOf[String],
                                      p.asInstanceOf[String],
                                      o.asInstanceOf[String])
               ))))
            case _ => None
        }
    }
}


object Foo {
   def parseRelations(s:String): Option[List[List[RelTriple]]] = {
       val fromInnerList = JsonHelper.fromJsonList(_:Any,RelTriple.fromJson)
       val fromOuterList = JsonHelper.fromJsonList(_:Any,fromInnerList)
       fromOuterList(JSON.parseFull(s))
   }
}

// FIXME: I'm sure there's a more idiomatic way of saying what I want here
object JsonHelper {
    def allDefined[A] (x:List[Option[A]]):Option[List[A]] = {
        if (x forall (x => x.isDefined)) {
            Some(x map (y => y.get))
        } else {
            None
        }
    }

    def fromJsonList[A](j:Any, f:Any => Option[A]):Option[List[A]] = {
        return j match {
          case x:List[Any] => allDefined(x map f)
          case _ => None
        }
    }
}