Inconsistencies in syntax when defining instances

[Adowrath]

I noticed, while reading part 3, "Instance Declarations", that you used two different syntaxes:
You start out with a :.

extension intAdditionSemigroup : new Semigroup[Int] {
  def combine(this x: Int)(y: Int) = x + y
}

But later on change that to a normal =:

  extension fooEq[A: Eq] = new Eq[Foo[A]] {
    def eqv(this x: Foo[A])(y: Foo[A]): Boolean =
      x.a.eqv(y.a)
  }

Further on, in part 4, you lose extension as a keyword and go back to implicit vals again. Same situation in the last part.

Which of the two do you intend?

---

Also, slight correction in the "Using default implementations" section:

extension readerApplicativeFunctor[R] :
  new Applicative[[A] => Reader[R, A]] with Functor[A] => Reader[R, A]] {
    def pure[A](a: A): Reader[R, A] =
      Reader(_ => a)

    def ap[A, B](this fa: Reader[R, A])(ff: Reader[R, A => B]): Reader[R, B] =
      Reader(r => ff.run(r)(fa.run(r)))
  }

Just syntactically, your Functor is missing a [ in there, but I don't think that you wrap square brackets around the types in kind-projector (correct me if I'm wrong, I've never used it).

[LukaJCB]

Thank you for pointing this out, I'll try to address it ASAP :)