What is the kind of Void?

Question

Seeing as the type of Void is uninhabited, can it be regarded as a type \"constructor\"? Or is this just a quick \"hack\" to be able to safely disregard / disable f

Answer 1

Luis Casillas showed that a polymorphic type can be uninhabited in vanilla Haskell. But there are also uninhabited monomorphic types. The classic one looks like this:

data Void = Void !Void

absurd :: Void -> a
absurd (Void x) = absurd x

Imagine trying to construct something of type Void.

void :: Void
void = Void _

You need something of type Void to fill the hole. Since that's the whole point of void, the only sensible choice is

void :: Void
void = Void void

If the Void constructor were lazy, that would be a cyclical structure Void (Void (Void ...)). But since it's strict, void can be written equivalently as

void = void `seq` Void void

which is obviously not going to fly.