Have you thought about adding [%derive.pp: <some-type>] ?

[chetmurthy]

there's [%show: int] etc, and that's useful. But I thought it mgiht be useful to have the same for Format-based pp-functions. I'm contemplating adding it to pa_ppx.deriving_plugins.show, and figured I'd see if you guys wanted to add the same here.

[cuihtlauac]

there's [%show: int] etc, and that's useful.

Useful indeed, and a pp-function thing would also be. It may even fix bugs:

type i = {
  j: int;
}

let f = [%show: i]

Error: Unbound value pp_i

A %% extension node is probably needed to handle the mutual recursion between pp and show.

[chetmurthy]

Um, I don't follow you. The type i is not annotated for deriving, so obviously it won't work. But this small change

# type i = {
  j: int;
}[@@deriving show]
let f = [%show: i] ;;
type i = { j : int; }
val pp_i :
  Ppx_deriving_runtime.Format.formatter -> i -> Ppx_deriving_runtime.unit =
  <fun>
val show_i : i -> Ppx_deriving_runtime.string = <fun>
val f : i -> string = <fun>

makes it work fine. Was there something else you were pointing-out?

[cuihtlauac]

I'm looking for a means to derive over types defined in dependencies that I don't want to change or duplicate. Does this make sense?

[chetmurthy]

Right, for that you can use ppx_import, yes? I do that pretty frequently.

[cuihtlauac]

It does the job. Thanks. I hadn't spotted that pattern yet. I'd also use what you're proposing.