Example of using Scala Parser Combinators to parse JSON into an AST

json.scala

import scala.util.parsing.combinator._

sealed trait Json

case object JsonNull extends Json
final case class JsonBoolean(b: Boolean) extends Json
final case class JsonString(s: String) extends Json
final case class JsonNumber(x: BigDecimal) extends Json
final case class JsonArray(elems: List[Json]) extends Json
final case class JsonObject(entries: List[(String, Json)]) extends Json

object Json extends JavaTokenParsers {

  def value: Parser[Json] = (
    obj
  | arr
  | stringLiteral ^^ JsonString
  | floatingPointNumber ^^ (s => JsonNumber(BigDecimal(s)))
  | "null" ^^ (_ => JsonNull)
  | "true" ^^ (_ => JsonBoolean(true))
  | "false" ^^ (_ => JsonBoolean(false))
  )

  def obj: Parser[JsonObject] = "{"~> repsep(member, ",") <~"}" ^^ JsonObject

  def arr: Parser[JsonArray] = "["~> repsep(value, ",") <~"]" ^^ JsonArray

  def member: Parser[(String, Json)] = stringLiteral~":"~value ^^ {
    case k~":"~v => k -> v
  }

  def parseAll(in: CharSequence): ParseResult[Json] = parseAll(value, in)
}