sam.scala

abstract class A[T, R]{ def apply(x: T): R }
val x: A[Int, Int] = x => x + 1
val x: A[Int, Int] = (x: Int) => x + 1
val x: A[String, Int] = (x: String) => 1
val x: A[String, Int] = (x: Object) => 1

val x: A[Object, Int] = (x: String) => 1 // error expected


object O {
  def m(a: A[Int, Int]) = 0
  def m(a: Int => Int) = 1
}
O.m(x => x)        // needs param type
O.m((x: Int) => x) // function type takes precedence


object O {
  def m(a: A[Int, Int]) = 0
  def m(f: (Int, Int) => Int) = 1
}
O.m(x => x)
O.m((x, y) => x)

object O {
  class Ev
  implicit object E1 extends Ev
  implicit object E2 extends Ev
  def m(a: A[Int, Int])(implicit ol: E1.type) = 0
  def m(a: A[String, Int])(implicit ol: E2.type) = 1
}
O.m((x: Int) => 1)
O.m((x: String) => 1)