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slowparse

This is just my experiment with parser combinators and Scala 3. Highly inspired by fastparse from Li Haoyi and talk from Scott Wlaschin. If you want to use parser combinators in your project, probably better use fastparse.

Example

The following parser will be able to parse a valid JSON. Also it can be found in JsonParserTest.scala.

import dev.vgerasimov.slowparse.Parsers.given
import dev.vgerasimov.slowparse.Parsers.*

// ... definitions of JSON classes are pretty straighforward, thus, omitted ...

val pNull: P[JNull.type] = P("null").map(_ => JNull)
val pBool: P[JBoolean] = (P("true").! | P("false").!).map(_.toBoolean).map(JBoolean(_))
val pNum: P[JNumber] =
  (anyCharIn("+-").? ~ d.+ ~ (P(".") ~ d.*).? ~ (anyCharIn("Ee") ~ anyCharIn("+-").? ~ d.*).?).!.map(_.toDouble)
    .map(JNumber(_))
val pStr: P[JString] = (P("\"") ~ until(P("\"")).! ~ P("\"")).map(JString(_))
val pChoice: P[Json] = P(choice(pNull, pBool, pNum, pStr, pArr, pObj))
val pArr: P[JArray] = P("[") ~~ pChoice.rep(sep = wss ~ P(",") ~ wss).map(JArray(_)) ~~ P("]")
val pObj: P[JObject] =
  val pair: P[(String, Json)] = pStr.map(_.v) ~~ P(":") ~~ pChoice
  val pairs: P[List[(String, Json)]] = pair.rep(sep = wss ~ P(",") ~ wss)
  P("{") ~~ pairs.map(_.toMap).map(JObject(_)) ~~ P("}")

val json: P[Json] = P(pObj | pArr)