scala-tokenizer-domain-model

name	scala-tokenizer-domain-model
description	Use when implementing tokenizer abstractions in Scala 2.13 — covers Token/TokenType ADTs, tokenizer traits, builder pattern, and batch processing conventions

Scala Tokenizer Domain Model

Core Data Types

TokenType ADT

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 Whitespace extends TokenType { val value = "whitespace" }
  case object Unknown  extends TokenType { val value = "unknown"  }

  // Lookup by string name
  def fromString(s: String): Option[TokenType] = s.toLowerCase match {
    case "string"     => Some(String)
    case "numeric"    => Some(Numeric)
    case "temporal"   => Some(Temporal)
    case "whitespace" => Some(Whitespace)
    case "unknown"    => Some(Unknown)
    case _            => None
  }
}

Token Case Class

case class Token(
  value: String,
  tokenType: TokenType,
  metadata: Map[String, Any] = Map.empty
) {
  def withMetadata(key: String, v: Any): Token =
    copy(metadata = metadata + (key -> v))

  def withMetadata(pairs: (String, Any)*): Token =
    copy(metadata = metadata ++ pairs)
}

Key design: copy() enables immutable updates — never mutate the token.

BaseTokenizer Trait

trait BaseTokenizer {
  /** Tokenize a single text input */
  def tokenize(text: String): List[Token]

  /** Tokenize a batch; default delegates to tokenize per element */
  def tokenizeBatch(texts: Seq[String]): List[List[Token]] =
    texts.toList.map(tokenize)
}

Concrete Tokenizers

StringTokenizer

class StringTokenizer(
  lowercase: Boolean = false,
  stripPunctuation: Boolean = false
) extends BaseTokenizer {

  override def tokenize(text: String): List[Token] = {
    val processed = if (lowercase) text.toLowerCase else text
    val cleaned   = if (stripPunctuation) processed.replaceAll("[^\\w\\s]", "") else processed
    cleaned.split("\\s+")
      .filter(_.nonEmpty)
      .map(w => Token(w, TokenType.String))
      .toList
  }
}

NumericTokenizer

class NumericTokenizer extends BaseTokenizer {
  private val numericPattern = """-?\d+(\.\d+)?""".r

  override def tokenize(text: String): List[Token] =
    numericPattern.findAllIn(text).toList
      .map(n => Token(n, TokenType.Numeric))
}

TemporalTokenizer

Uses regex to find dates/times:

class TemporalTokenizer extends BaseTokenizer {
  private val datePattern =
    """\d{4}-\d{2}-\d{2}|\d{2}/\d{2}/\d{4}""".r

  override def tokenize(text: String): List[Token] =
    datePattern.findAllIn(text).toList
      .map(d => Token(d, TokenType.Temporal))
}

WhitespaceTokenizer

class WhitespaceTokenizer extends BaseTokenizer {
  override def tokenize(text: String): List[Token] =
    text.split("\\s+")
      .filter(_.nonEmpty)
      .map(w => Token(w, TokenType.Whitespace))
      .toList
}

UniversalTokenizer

Delegates to multiple tokenizers and merges/deduplicates:

class UniversalTokenizer(tokenizers: List[BaseTokenizer]) extends BaseTokenizer {
  override def tokenize(text: String): List[Token] =
    tokenizers.flatMap(_.tokenize(text))
}

Builder Pattern

class TokenizerBuilder {
  private var tokenizers: List[BaseTokenizer] = List.empty

  def withStringTokenizer(
    lowercase: Boolean = false,
    stripPunctuation: Boolean = false
  ): TokenizerBuilder = {
    tokenizers = tokenizers :+ new StringTokenizer(lowercase, stripPunctuation)
    this
  }

  def withNumericTokenizer(): TokenizerBuilder = {
    tokenizers = tokenizers :+ new NumericTokenizer()
    this
  }

  def withTemporalTokenizer(): TokenizerBuilder = {
    tokenizers = tokenizers :+ new TemporalTokenizer()
    this
  }

  def withWhitespaceTokenizer(): TokenizerBuilder = {
    tokenizers = tokenizers :+ new WhitespaceTokenizer()
    this
  }

  def build(): UniversalTokenizer = new UniversalTokenizer(tokenizers)
}

object TokenizerBuilder {
  def apply(): TokenizerBuilder = new TokenizerBuilder()
}

Top-Level Functions

These are placed in a package object or standalone object:

object Tokenizer {
  /** Tokenize a single text with the given tokenizer */
  def tokenize(text: String, tokenizer: BaseTokenizer): List[Token] =
    tokenizer.tokenize(text)

  /** Batch tokenize */
  def tokenizeBatch(
    texts: Seq[String],
    tokenizer: BaseTokenizer
  ): List[List[Token]] =
    tokenizer.tokenizeBatch(texts)

  /** Convert a raw string to a Token with inferred type */
  def toToken(value: String, tokenType: TokenType): Token =
    Token(value, tokenType)

  /** Add metadata to a token */
  def withMetadata(token: Token, key: String, v: Any): Token =
    token.withMetadata(key, v)
}

Idiomatic Scala Patterns for Tokenizers

Use Regex from scala.util.matching

import scala.util.matching.Regex
val pattern: Regex = """\d+""".r
pattern.findAllIn(text).toList

Avoid null — use Option

def safeTokenize(text: String): Option[List[Token]] =
  Option(text).filter(_.nonEmpty).map(tokenize)

Use flatMap / collect for filtering-with-transform

tokens.collect { case t if t.tokenType == TokenType.Numeric => t.value }

Immutability by Default

• All Token fields are val (enforced by case class)
• Builder accumulates with :+ and returns this for chaining
• copy() for "modification"

Error Handling in Tokenization

import scala.util.{Try, Success, Failure}

def safeParse(text: String): Try[List[Token]] =
  Try(tokenize(text)).recoverWith {
    case e: IllegalArgumentException =>
      Failure(new RuntimeException(s"Bad input: $text", e))
  }