type ResultOf[Function] = {
  type Result
}
object ResultOf {
  type ResultOfFunction1[A, R] = ResultOf[A => R] {
    type Result = R
  }
  implicit def resultOfFunction1[A, R]: ResultOfFunction1[A, R] = null
}
def betterImplicitly[RequiredType][ActuallyType](implicit i: RequiredType with ActuallyType) = i
val functionTypeTrait = betterImplicitly[ResultOf[String => Int]]
val shouldBeInt: functionTypeTrait.Result = 0

import scala.language.higherKinds

type Curry2[F[_, _]] = {
  type Apply[A] = {
    type Apply[B] = F[A, B]
  }
}

trait Functor[F[_]] {
  def map[A, B](op: A => B)(orig: F[A]): F[B]
}

type Reader = Curry2[Function]

implicit def ReaderFunctor[R] = new Functor[Reader#Apply[R]#Apply] {
  override def map[A, B](op: A => B)(orig: R => A): R => B =
    orig andThen op
}

def map[A,B,F[_]](op: A => B)(fa: F[A])(implicit functor: Functor[F]): F[B] =
  functor.map(op)(fa)

def toStringContainer[F[_]](a: F[Int])(implicit functor: Functor[F]) = map[Int, String, F](_.toString)(a)

val id: Int => Int = identity

val out: Int => String = toStringContainer[Reader#Apply[Int]#Apply](id)
out(2)

import scala.language.higherKinds

type Curry2[F[_, _]][A][B] = F[A, B]

trait Functor[F[_]] {
  def map[A, B](op: A => B)(orig: F[A]): F[B]
}

type Reader = Curry2[Function]

implicit def ReaderFunctor[R] = new Functor[Reader[R]] {
  override def map[A, B](op: A => B)(orig: R => A): R => B =
    orig andThen op
}

def map[A,B][F[_]](op: A => B)(fa: F[A])(implicit functor: Functor[F]): F[B] =
  functor.map(op)(fa)

/*
  Not sure if it would be possible to get this clean,
  or if the implicit would cause this to fail.
  Might also have to pass toString like `(_:Int).toString`
*/
def toStringContainer = map(_.toString)

val id: Int => Int = identity

val out: Int => String = toStringContainer[Reader[Int]](id)
out(2)

% scala-cli -S 3.nightly
Welcome to Scala 3.3.1-RC1-bin-20230331-7262437-NIGHTLY-git-7262437
scala> import scala.language.experimental.clauseInterleaving
scala> def foo[A](x: A)[B](y: B) = (x, y)
def foo[A](x: A)[B](y: B): (A, B)