Install and use the "with-utf8" package

[aabounegm]

To support other locales on systems that do not default to UTF-8

[fizruk]

For context: we have encountered that Unicode syntax in Rzk breaks on systems with non-standard locales (e.g. German locales in particular). Which resulted in weird syntax errors for some (but not all!) Unicode symbols used. This PR should fix the issue for everyone 🤞

[fizruk]

@deemp it appears that cabal2nix cannot properly handle conditionals, so I had to remove with-utf8 from rzk.nix manually and comment out the use of hpack there as well. This solves the problem, but we now have to repeat this operation every time we update the cabal file and use cabal2nix. Also, this way rzk.nix cannot really build the executable, so it is probably broken for non-GHCJS builds. Perhaps, you know of a better approach here?

[deemp]

Is the final goal to build try-rzk via GHCJS without with-utf8?

The flake.nix provides packages.rzk for non-GHCJS builds and packages.try-rzk for GHCJS builds. It doesn't use rzk.nix.

Later, I can add a default.nix and shell.nix so that people without flakes can get packages and devShells.default.

packages.rzk relies on rzk.cabal manually generated using hpack. It also calls cabal2nix via callCabal2nix. It's possible to override dependencies (necessary Haskell packages) of rzk for GHCJS and non-GHCJS builds.

If I understand the goal correctly, I need to nullify the with-utf8 for GHCJS builds in flake.nix.

[fizruk]

Is the final goal to build try-rzk via GHCJS without with-utf8?

Yes, with-utf8 should only be used with GHC, not GHCJS.