Scala Code of Andrea Munarin 10/03/00 for Bending Spoons

/**
  * Redefine the Monad type class for the Maybe type
  */
enum MyMaybe[+A]:
    case OK(x: A)
    case KO

/**
  * Define the Monad type class. For the Monad type class, define the unit, flatmap and map methods.
  */
trait Monad[F[_]]:
    def unit[A](z: A): F[A]
    extension[A](o: F[A])
        def flatmap[B](f: A=>F[B]): F[B]
        def map[B](f: A=>B): F[B]

import MyMaybe.*

/**
  * Define the Monad type class for the Maybe type implementing the unit, flatmap and map methods.
  */
given Monad[MyMaybe] with
    def unit[A](z:A):MyMaybe[A] = OK(z)
    extension [A](o: MyMaybe[A])
        def flatmap[B](f: A=>MyMaybe[B]): MyMaybe[B] =
            o match
                case KO=>KO
                case OK(x)=>f(x)
        def map[B](f: A=>B): MyMaybe[B] =
            o match
                case KO=>KO
                case OK(x)=>unit((f(x)))

/**
  * Define the perdue method that takes a T[Int] and returns a T[Int] with the value doubled.
  * T is a Monad or a subtype of Monad
  * @param o the T[Int] to double
  * @return the T[Int] with the value doubled
  */
def perdue[T[_]:Monad](o:T[Int]):T[Int]=
    o.map(x=>x*2)