negation of a type

[juan_gandhi]

(from Miles Sabin's post)

// Encoding for "A is not a subtype of B"
trait <:!<[A, B]

// Uses ambiguity to rule out the cases we're trying to exclude
implicit def nsub[A, B] : A <:!< B = null
implicit def nsubAmbig1[A, B >: A] : A <:!< B = null
implicit def nsubAmbig2[A, B >: A] : A <:!< B = null

// Type alias for context bound
type |¬|[T] = {
 type λ[U] = U <:!< T
}

def foo[T, R : |¬|[Unit]#λ](t : T)(f : T => R) = f(t)

foo(23)(_ + 1)   // OK
foo(23)(println) // Doesn't compile

(src)