run2-circe-json

name	run2_circe-json
description	Using Circe for JSON tokenization and dot-path navigation in Scala, with the exact APIs needed to replace Python's json module and dict traversal.

Circe JSON Library (replacing Python's json module)

Setup (build.sbt)

libraryDependencies ++= Seq(
  "io.circe" %% "circe-core"    % "0.14.6",
  "io.circe" %% "circe-generic" % "0.14.6",
  "io.circe" %% "circe-parser"  % "0.14.6"
)

Imports

import io.circe.Json
import io.circe.parser._   // for parse()
import io.circe.syntax._   // for .asJson (not needed for tokenizer)

Serialization

Python:

json.dumps(value)            # compact
json.dumps(value, indent=2)  # pretty

Circe:

value.noSpaces   // compact — equivalent to json.dumps(value)
value.spaces2    // 2-space indent — equivalent to json.dumps(value, indent=2)
value.spaces4    // 4-space indent

Parsing

val json: Either[io.circe.Error, Json] = parse("""{"key": "value"}""")
val json: Json = parse("""{"key": "value"}""").getOrElse(Json.Null)

Key Json Navigation APIs

json.asObject             // Option[JsonObject] — access if json is an object
jsonObj.apply("key")      // Option[Json] — get field by name
json.asArray              // Option[Vector[Json]] — access if json is an array
arr.lift(idx)             // Option[Json] — safe array index (None if out of bounds)
json.asString             // Option[String]
json.asNumber             // Option[JsonNumber]
json.asBoolean            // Option[Boolean]
Json.Null                 // null Json value

Dot-Path Navigation (replacing Python dict/list traversal)

Python:

def tokenize_path(self, value: JsonValue, path: str) -> Token | None:
    parts = path.split(".")
    current = value
    for part in parts:
        if isinstance(current, dict) and part in current:
            current = current[part]
        elif isinstance(current, list) and part.isdigit():
            idx = int(part)
            current = current[idx] if 0 <= idx < len(current) else return None
        else:
            return None
    return self.tokenize(current)

Scala with Circe (functional foldLeft):

def tokenizePath(value: Json, path: String): Option[Token] = {
  val parts = path.split("\\.").toList
  val leaf  = parts.foldLeft(Option(value)) { (current, part) =>
    current.flatMap { json =>
      json.asObject.flatMap(_.apply(part))
        .orElse(
          part.toIntOption.flatMap(idx =>
            json.asArray.flatMap(arr => arr.lift(idx))
          )
        )
    }
  }
  leaf.map(tokenize)
}

Key idiomatic choices:

• Option[Json] as the accumulator — None propagates failures automatically
• flatMap chains: each step returns None if navigation fails, foldLeft propagates it
• part.toIntOption (Scala 2.13+) — safe string-to-int, replaces part.isdigit() + int(part)
• arr.lift(idx) — safe array access (None if out of bounds), replaces bounds check

Complete JsonTokenizer

final class JsonTokenizer(pretty: Boolean = false) {

  def tokenize(value: Json): Token = {
    val jsonStr = if (pretty) value.spaces2 else value.noSpaces
    Token(jsonStr, TokenType.STRUCTURED, Map("json" -> true))
  }

  def tokenizePath(value: Json, path: String): Option[Token] = {
    val parts = path.split("\\.").toList
    parts.foldLeft(Option(value)) { (current, part) =>
      current.flatMap { json =>
        json.asObject.flatMap(_.apply(part))
          .orElse(part.toIntOption.flatMap(idx =>
            json.asArray.flatMap(_.lift(idx))
          ))
      }
    }.map(tokenize)
  }
}