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commercialhaskell / rio

A standard library for Haskell
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A (draft of a) mixin-based template #229

Closed dequbed closed 3 years ago

dequbed commented 3 years ago

Cabal 2.0/GHC 8.2 (and later) support mixins to rename, show, and hide modules.

We can use those mixins to not have to use NoImplicitPrelude and instead treat RIO as a 'true' Prelude-replacement, i.e. changing the import Path to Prelude-prefixed so instead of import RIO.File one uses import Prelude.File.

While this may not be the best way of using RIO it is basically how I've been using RIO in my private projects and I wanted to show this way in case anybody else finds it interesting. The actual code itself could also be improved a lot but I kept as close as possible to the original template this was copied from to make the differences obvious. Biggest drawback(s) of this approach is that the file src/Prelude.hs which provides the Prelude module is absolutely required for the build process, that this fact is not very obvious, and that if you drop this file or have a very different folder structure the errors you will get are very much not helpful.

This template may not be something you want in the upstream repo in which case feel free to close this PR and/or give me a pointer to where this would be more suited. Otherwise this still needs to actually be integrated because I don't know how stack templates work and I didn't want to break anybodies builds by making a mistake there.

snoyberg commented 3 years ago

I'd be happy to include a link to it in a different repo, but I'm not ready to promote it inside this repo. I haven't used mixins myself and am a bit concerned about some of these features. I'm also not certain I understand why we'd want to encourage people to import Prelude.File instead of RIO.File. And finally, maintaining this list of module renames while rio evolves seems like overhead that we'll forget to do.

dequbed commented 3 years ago

I'd be happy to include a link to it in a different repo, but I'm not ready to promote it inside this repo. I haven't used mixins myself and am a bit concerned about some of these features. I'm also not certain I understand why we'd want to encourage people to import Prelude.File instead of RIO.File. And finally, maintaining this list of module renames while rio evolves seems like overhead that we'll forget to do.

Understandable, especially the last point is something I was concerned about as well and I don't see a good solution either. I'll close this PR. (Re. your why not use the RIO module i.e. RIO.File: It's a comfort feature - you don't have to use NoImplicitPrelude anywhere)

Cheers and thanks for writing & maintaining RIO, it's a wonderful framework for writing Haskell :)