[@@deriving pp]

[giltho]

Hello,

I'm not 100% sure this isn't already implemented but, at the moment, I believe that the only option for obtaining a printer is to use [@@deriving show]. This also generates a show function, which I often do not want, it clutters my APIs and whenever I want to write the printer by hand it forces me to also add the show function everywhere even though I never use it.

Would you be interested in having [@@deriving pp] in addition to [@@deriving show] which would do the same thing but only derive the pp function and note the show function?

Happy to implement this myself if there is agreement :)

[gasche]

Sure, this sounds like a reasonable thing to do.

Warning: the current ppx_deriving codebase is obscure, its first versions predate ppxlib, it had uneven maintenance over the years and has been the rough transition of being ported onto ppxlib, so there is baggage you see when you look at the code.

You would look at src_plugins/show/ppx_deriving_show.ml. The easiest option I believe would be to add a new ppxlib transformation from that module, that declares derive.pp (in addition to derive.show). If things were done from the scratch you would instead want a separate src_plugins/pp/ppx_deriving_pp.ml, and then figure out how to share enough code/logic with the "show" plugin to avoid duplication. I would not try to do this because it's going to be unpleasant (more refactoring work on the baggage). The only downside that I can see in the easy route I propose is that the package/library name will remain ppx_deriving.show, even for users of pp only. There may be an easy way to declare ppx_deriving.pp as an alias of ppx_deriving.show (or otherwise export a trivial package depending on show), but this is outside the scope of what I'm motivated to lookup right now.

[giltho]

To be fair, I'm not sure it makes much sense to separate pp and show into different packages with shared logic. It makes a lot of sense for these two to come in the same package anyway