Conceptパターンを再帰的にやってみた

gistfile1.sbt

scala> import Json._
import Json._

scala> toJson(List(10, 20, 30))
res0: String = [10, 20, 30]

scala> toJson(List("aaa", "bbb", "ccc"))
res1: String = ["aaa", "bbb", "ccc"]

scala> toJson(List(List(1, 2, 3), List(4, 5), List(6, 7, 8, 9)))
res2: String = [[1, 2, 3], [4, 5], [6, 7, 8, 9]]

scala> toJson(List(Map("aaa" -> List(1, 2), "bbb" -> List(3)), Map("ccc" -> List(4, 5, 6), "ddd" -> List())))
res3: String = [{"aaa": [1, 2], "bbb": [3]}, {"ccc": [4, 5, 6], "ddd": []}]

Json.scala

object Json {

  trait ToJson[-A] {
    def apply(value: A): String
  }

  def toJson[A](value: A)(implicit t: ToJson[A]): String = t(value)

  implicit def traversableToJson[A](implicit t: ToJson[A]) = new ToJson[Traversable[A]] {
    def apply(value: Traversable[A]): String = value.map(n => toJson(n)).mkString("[", ", ", "]")
  }

  implicit def mapToJson[A, B](implicit t: ToJson[B]) = new ToJson[Map[A, B]] {
    def apply(value: Map[A, B]): String = value.map {
      case (k, v) => toJson(k.toString) + ": " + toJson(v)
    }.mkString("{", ", ", "}")
  }

  implicit val stringToJson = new ToJson[String] {
    def apply(value: String): String = "\"" + value + "\""
  }

  implicit val intToJson = new ToJson[Int] {
    def apply(value: Int): String = value.toString
  }

}