Lifting Pretty to * -> * & * -> * -> *

[robrix]

Would you be open to a PR defining liftings of Pretty to * -> * and * -> * -> *, a la Show1 &c. from Data.Functor.Classes? It makes (decidable) recursive instances for Fix, Free, Cofree &c. much easier to define:

instance Pretty1 f => Pretty (Fix f) where
  pretty (Fix f) = liftPretty pretty prettyList f

If so, I’ll be happy to submit one 😊

[robrix]

For reference, here’s the implementation I’m working with currently:

https://github.com/robrix/abstract-interpretation/blob/b90ea99a977872fd1e31560b579c6cdfec33f6f7/src/Data/Functor/Classes/Pretty.hs

(I’d document everything before submission, of course.)

[quchen]

Hm, the code doesn’t really look very nice, but since we now have Show1 etc. in Base, I think this is something we could include. I’d like to keep it minimally invasive though – from a Haddock standpoint, there shouldn’t be too many new exports, the (single exposed main) module is long enough as it is.

Can you explain why Pretty1Of is necessary a bit? I’m familiar with Show1, but not with Show1Of.

[robrix]

Hm, the code doesn’t really look very nice, but since we now have Show1 etc. in Base, I think this is something we could include.

I’ll do my best to match project style 😊

I’d like to keep it minimally invasive though – from a Haddock standpoint, there shouldn’t be too many new exports, the (single exposed main) module is long enough as it is.

Okay, you bet 👍

Would you be interested in including a generically-derivable implementation of Pretty1? This really isn’t make-or-break for me; we can always include it in our project and replace deriving Pretty1 with instance Pretty1 F where liftPretty = genericLiftPretty.

I’m guessing not given the above, but wanted to double-check since it wouldn’t necessarily have to increase the API’s surface area.

Can you explain why Pretty1Of is necessary a bit? I’m familiar with Show1, but not with Show1Of.

Oh, my bad—I don’t think we should include it at all. It’s a convenience to give you a Pretty instance if you have a Pretty1 instance, and helps to avoid orphan instances. I see little benefit to including it here, because presumably we’d just write a (non-orphan) Pretty instance in the first place.

[quchen]

I don’t think Pretty1 should be derivable (likewise for Pretty), since prettiness is not something that follows any laws. If push comes to shove and we really need a quick Pretty instance, writing the instance without any definitions will just fall back to Show.

[quchen]

I’m closing this issue since the corresponding PR (#40) looks good enough to subsume it.