EqualAndMonoid.scala

trait Equal[-A] extends EqualLaws[A] {
  def equal(a: A, b: A): Boolean  
}

object Equal {
  implicit val equalInt: Equal[Int] = new Equal[Int] {
     def equal(a: Int, b: Int) = a == b
  }
}

trait Monoid[A] extends MonoidLaws[A] {
   def zero: A
   def append(a: A, b: A): A
}

object Monoid {
  implicit val monoidInt: Monoid[Int] = new Monoid[Int] {
    def zero = 0
    def append(a: Int, b: Int) = a + b
  }
}


trait Foo {
 type MyType 
 def get: MyType
}

val foo: Foo = new Foo {
   type MyType = Int
   def get: MyType = 1
}

val int: Int = foo.get 
// compile time error. Scala doesn't the foo: Foo hold an Int, but we know it is definitely an Int