#Recursive class #Json #Reads using #lazyRead feature #Play21 #scala A class inheriting a parent trait with a member of the parent type

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CODE.scala

sealed abstract trait Tree
case class Leaf(a: String) extends Tree
case class Node(l: Tree, r: Tree) extends Tree
 
implicit val treeR: Reads[Tree] =
__.read[Leaf].map(x => x:Tree) orElse
(
(__ \ "l").lazyRead(treeR) and (__ \ "r").lazyRead(treeR)
)(Node.apply _).map(x => x:Tree)
 
scala> treeR.reads(Json.obj("a" -> "toto"))
res10: play.api.libs.json.JsResult[Tree] = JsSuccess(Leaf(toto),/a)
 
scala> treeR.reads(Json.obj("l" -> Json.obj("a" -> "toto"), "r" -> Json.obj("a" -> "tata")))
res11: play.api.libs.json.JsResult[Tree] = JsSuccess(Node(Leaf(toto),Leaf(tata)),)

code:

 implicit val leafReads =  ((__ \ "a").read[String] ) map ( x => Leaf(x))

 implicit val treeReads:Reads[Tree] = (__.read[Leaf]) map( x => x:Tree) orElse
     (
       ( __ \ "l").lazyRead(treeReads) and
       ( __ \ "r").lazyRead(treeReads)
    ) (Node.apply _) map (x => x:Tree)   

---

gives out this error :
Error:(109, 41) forward reference extends over definition of value treeReads
( __ \ "l").lazyRead(treeReads) and