Re: [Haskell-cafe] Polykinded promoted types

2014-12-09 0:04 GMT+01:00 Taylor Hedberg :

$ ghci -XDataKinds -XKindSignatures Prelude> data K = K Prelude> data Foo (a :: K) = Foo Prelude> :kind Foo Foo :: K -> *

Note that types with kinds other than * are uninhabited, so you can't write a version of Maybe with that kind (because the Just constructor would require a value that can't exist).

That was quick (and that is that I feared). Thanks anyway.