gistfile1.scala

trait A
trait B
trait E

trait S {
  def publish(e: E): Unit
}

object Foo {
  def p[F[+_]](f: F[E])(implicit F: Functor[F], s: S): F[Unit] = f.map(s.publish)

  def fn(a: A, b: B): E = new E {}

  def test {
    implicit val s = new S { def publish(e: E) {} }
    p(fn) // lol no
    // I want what's effectively an identity function i can pimp onto fn so I can go
    p(fn.i)
    // and have things actually compile
  }
}

e.g. p[({ type l[+a] = (A, B) => a })#l](fn) works but is ugly.

How horrible is this? :)

object fn extends Function2[A, B, E] {
  type L[+Z] = (A, B) => Z
  def apply(a: A, b: B): E = new E{}
}

p[fn.L](fn)

That's… striking.