With the coming of Haskell 9.0.1, we also got a package-management tool of Haskell, Document is here.

First , you must have a old version of GHC, and want to try the new features.

Then it worked like this:

1. install new version GHC
2. set new version as default
3. check

ghcup install ghc 9.0.1
ghcup set ghc 9.0.1
ghc --version