On 7/8/2017 7:01 PM, sarn wrote:
On Sunday, 9 July 2017 at 00:16:50 UTC, Walter Bright wrote:
We have types that cannot be named (Voldemort types), types that have no type
(void), I suppose that types that cannot exist will fill out the edge cases of
the menagerie.
I assume there is a standard jargon for this - does anyone know Type Theory?
Are there any other interesting uses for a type that cannot exist?
In pure functional languages, that's what "bottom" or Haskell's Void is.
In Curry–Howard "programs are proofs" theory, a type is a proposition and an
instance is a proof. A type with no instance is a proposition that can't be
proved.
https://codewords.recurse.com/issues/one/type-systems-and-logic
I'm not sure how much impact this has on everyday D programming, but hey, it's a
thing.
Thanks, it looks like we won't get any help from type theory. We're on our own
:-)
(D already has a `void` type, so can't use Haskell's word.)
