run2-scala-idiomatic-fp

name	run2_scala-idiomatic-fp
description	Refined FP patterns for Functors and Monads in Scala, including applicative.

Idiomatic FP in Scala

Functors and Monads

A proper Functor should be covariant. A Monad should provide pure and flatMap.

class TokenFunctor[+T](val value: T) {
  def map[U](f: T => U): TokenFunctor[U] = new TokenFunctor(f(value))
}

class TokenMonad[+T](value: T) extends TokenFunctor[T](value) {
  def flatMap[U](f: T => TokenMonad[U]): TokenMonad[U] = f(value)
  
  // Applicative: apply a wrapped function to a wrapped value
  def ap[U, V](ff: TokenMonad[U => V])(implicit ev: T <:< U): TokenMonad[V] = {
    ff.flatMap(f => TokenMonad.pure(f(value)))
  }
}

object TokenMonad {
  def pure[T](v: T): TokenMonad[T] = new TokenMonad(v)
}

Abstract Tokenizer with Covariance/Contravariance

trait BaseTokenizer[-T] {
  def tokenize(value: T): Token
}

If a tokenizer only consumes T, it should be contravariant in T.