Recursive extraction in Rapture JSON

recursive.scala

// Rapture imports
import rapture.json._
import jsonBackends.jawn._

// Define our AST
class Op(val opName: String) extends AnyVal { override def toString = opName }
sealed trait ExprTree
case class Ident(name: String) extends ExprTree { override def toString = name }
case class Expr(left: ExprTree, op: Op, right: ExprTree) extends ExprTree { override def toString = s"$left $op $right" }

// No implicit extractor for `ExprTree`s exists, so we need to define it by composing existing extractors
implicit def extractor: Extractor[ExprTree, Json] = Json.extractor[Ident] orElse Json.extractor[Expr]

// Let's create a sample JSON value:
val j = json"""{"left":{"left":{"name":"alpha"},"op":"+","right":{"name":"beta"}},"op":"*","right":{"left":{"name":"gamma"},"op":"/","right":{"name":"delta"}}}"""

val exprTree = j.as[ExprTree]
// Yields exprTree: ExprTree = alpha + beta * gamma / delta