Hi, vscode should show you any error or warning in the editor itself without having to open a repl session if you dont want to, so maybe it is not working correctly.
It also should let available other interesting features, you can see a list with demos here: Features — haskell-language-server 1.3.0 documentation
If it is not working for you, please, follow those steps to recollect info and open an issue in the hls repo.