Unwrapping the value of an Identity monad

Question

I have been playing a little bit with scalaz and I am stuck on a seemingly trivial issue. I was playing around with the Reader and Kliesli monads and found myself with something like this:

val gr = Reader { (_: Int) + 1 }
val a = gr(1)

That dutifully responds:

a: scalaz.Id.Id[Int] = 2

What I am trying to do now is to unwrap the Int from the Identity monad, for that I should be using the ?? operator, with this signature:

final def ??(d: => A)(implicit ev: Null <:< A): A

The first parameter I should pass is a default value, a call by name Int (as pointed by Brian McCutchon) :

scala> a??(1)
<console>:19: error: Cannot prove that Null <:<   scalaz.Id.Id[Int].
   a??(1)
    ^

I would like to understand what I am missing here before I keep moving. Thanks EDITED to fix my confusion about call-by-name with no parameters function. Shame.

Answer 1

a is already an Int; see the definition.

edit: There are no methods to unwrap because there is nothing to unwrap; the type the REPL prints for a is just another way of saying Int.