‘:kind () :: '()’ doesn't give any output
$ ./ghc/_build/stage1/bin/ghc -ignore-dot-ghci --interactive
GHCi, version 9.1.0.20201202: https://www.haskell.org/ghc/ :? for help
ghci> :set -XKindSignatures -XDataKinds
ghci> :k () :: '()
ghci>
ghci> :set -XPartialTypeSignatures -Wno-partial-type-signatures
ghci> :k (_, _) :: '(_, _)
ghci>
ghci> import Data.Functor.Identity
ghci> :k Identity _ :: 'Identity _
ghci>It should give an error