json.md

Expression

• Expression을 BNF 로 표현하면 다음과 같다

Expression ::= Addition left:Expression right:Expression
             | Subtraction left:Expression right:Expression
             | Division left:Expression right:Expression
             | SquareRoot value:Expression
             | Number value:Int

JSON

• JSON 을 BNF 로 표현하면 다음과 같다

Json ::= JsNumber value:Double
       | JsString value:String
       | JsBoolean value:Boolean
       | JsNull
       | JsSequence
       | JsObject
JsSequence ::= SeqCell head:Json tail:JsSequence
             | SeqEnd
JsObject ::= ObjectCell key:String value:Json tail:JsObject
           | ObjectEnd

JSON

• scala 코드로 표현하면 다음과 같다

sealed trait Json
final case class JsNumber(value: Double) extends Json
final case class JsString(value: String) extends Json
final case class JsBoolean(value: Boolean) extends Json
case object JsNull extends Json
sealed trait JsSequence extends Json
final case class SeqCell(head: Json, tail: JsSequence) extends JsSequence
case object SeqEnd extends JsSequence
sealed trait JsObject extends Json
final case class ObjectCell(key: String, value: Json, tail: JsObject) extends JsObject
case object ObjectEnd extends JsObject

JSON 객체 구현

object json {
  sealed trait Json {
    def print: String = {
      def quote(s: String): String =
        '"'.toString ++ s ++ '"'.toString
      def seqToJson(seq: SeqCell): String =
        seq match {
          case SeqCell(h, t @ SeqCell(_, _)) =>
            s"${h.print}, ${seqToJson(t)}"
          case SeqCell(h, SeqEnd) => h.print
        }

      def objectToJson(obj: ObjectCell): String =
        obj match {
          case ObjectCell(k, v, t @ ObjectCell(_, _, _)) =>
            s"${quote(k)}: ${v.print}, ${objectToJson(t)}"
          case ObjectCell(k, v, ObjectEnd) =>
            s"${quote(k)}: ${v.print}"
        }

      this match {
        case JsNumber(v) => v.toString
        case JsString(v) => quote(v)
        case JsBoolean(v) => v.toString
        case JsNull => "null"
        case s @ SeqCell(_, _) => "[" ++ seqToJson(s) ++ "]"
        case SeqEnd => "[]"
        case o @ ObjectCell(_, _, _) => "{" ++ objectToJson(o) ++ "}"
        case ObjectEnd => "{}"
      }
    }
  }
  final case class JsNumber(value: Double) extends Json
  final case class JsString(value: String) extends Json
  final case class JsBoolean(value: Boolean) extends Json
  case object JsNull extends Json
  sealed trait JsSequence extends Json
  final case class SeqCell(head: Json, tail: JsSequence) extends JsSequence
  case object SeqEnd extends JsSequence
  sealed trait JsObject extends Json
  final case class ObjectCell(key: String, value: Json, tail: JsObject) extends JsObject
  case object ObjectEnd extends JsObject
}