scala-adt-enums

Scala ADTs, Sealed Traits, and Enums for Python Developers

Enums

Python Enum

from enum import Enum

class TokenType(Enum):
    STRING = "string"
    NUMERIC = "numeric"
    TEMPORAL = "temporal"
    STRUCTURED = "structured"
    BINARY = "binary"
    NULL = "null"

# Usage
t = TokenType.STRING
t.value  # "string"
t.name   # "STRING"

Scala Enum (Scala 2.13 - using sealed trait + case objects)

sealed trait TokenType {
  def value: String
}
object TokenType {
  case object STRING extends TokenType { val value = "string" }
  case object NUMERIC extends TokenType { val value = "numeric" }
  case object TEMPORAL extends TokenType { val value = "temporal" }
  case object STRUCTURED extends TokenType { val value = "structured" }
  case object BINARY extends TokenType { val value = "binary" }
  case object NULL extends TokenType { val value = "null" }

  // Helper for pattern matching
  def all: List[TokenType] = List(STRING, NUMERIC, TEMPORAL, STRUCTURED, BINARY, NULL)
}

// Usage
val t: TokenType = TokenType.STRING
t.value  // "string"

Algebraic Data Types (ADTs)

Python Union Types

from typing import Union

JsonValue = Union[str, int, float, bool, None, list["JsonValue"], dict[str, "JsonValue"]]

# Function handling multiple types
def process(value: Union[str, int]) -> str:
    if isinstance(value, str):
        return value
    else:
        return str(value)

Scala Sealed Traits (Idiomatic ADT)

sealed trait JsonValue
case class JString(value: String) extends JsonValue
case class JNumber(value: Double) extends JsonValue
case class JBoolean(value: Boolean) extends JsonValue
case object JNull extends JsonValue
case class JArray(value: Vector[JsonValue]) extends JsonValue
case class JObject(value: Map[String, JsonValue]) extends JsonValue

// Pattern matching (exhaustive)
def process(json: JsonValue): String = json match {
  case JString(s) => s
  case JNumber(n) => n.toString
  case JBoolean(b) => b.toString
  case JNull => "null"
  case JArray(arr) => s"Array(${arr.size})"
  case JObject(obj) => s"Object(${obj.size})"
}