tagless.scala

import cats.effect._
import scala.concurrent.duration._

def addCoffeePowder(pot: Pot): IO[Pot] = ???

def addWater(pot: Pot): IO[Pot] = ???

def waitUntilBoil(heatedPot: Pot): StateT[IO, Unit, FiniteDuration] = ???

def makeCoffee(pot: Pot): IO[Coffee] = {
  for {
    withCoffeePwd <- addCoffeePowder(pot)
    withWater     <- addWater(withCoffeePwd)
    heatedPot     <- turnOnHeat(withWater)
    _             <- waitUntilBoil(heatedPot)   // wont compile
    coffee        <- pot.pourCoffee
  } yield coffee
}

-----------

def addCoffeePowder[F[_]](pot: Pot): F[Pot] = ???

def addWater[F[_]](pot: Pot): F[Pot] = ???

type DurationState[F[_]] = Stateful[F, FiniteDuration]

def waitUntilBoil[F[_]: DurationState](heatedPot: Pot): F[Unit] = ???

def makeCoffee[F[_]: DurationState](pot: Pot): F[Coffee] = {
  for {
    withCoffeePwd <- addCoffeePowder(pot)
    withWater     <- addWater(withCoffeePwd)
    heatedPot     <- turnOnHeat(withWater)
    _             <- waitUntilBoil(heatedPot)   // compiles without addWater and addCoffeePowder knowing anything about State
    coffee        <- pot.pourCoffee
  } yield coffee
}