Haskell Weird Kinds
- by SHiNKiROU
When I was experimenting with Haskell kinds, and trying to get the kind of ->, and this showed up:
$ ghci
...
Prelude> :k (->)
(->) :: ?? -> ? -> *
Prelude>
Instead of the expected * -> * -> *.
What are the ?? and ? things? Do they mean concrete types or "kind variables"? Or something else?