How to compile?

[neojski]

I wanted to play with this code a little bit but I have some troubles compiling it. Would you mind adding some instructions to the README?

[paurkedal]

Just added some instructions, please try and let me know of any issues.

[neojski]

It's helpful, now it complies. However, I tried using it as described in whitequark's blog post via:

ocamlfind ocamlc -package ppx_deriving_random examples/free_magma.ml -verbose

but it says:

Effective set of compiler predicates: pkg_ppx_deriving_random,autolink,byte
+ ocamlc.opt -verbose -I /home/neo/.opam/system/lib/ppx_deriving_random examples/free_magma.ml
File "examples/free_magma.ml", line 12, characters 23-25:
Error: Syntax error
ocamlc.opt returned with exit code 2

[paurkedal]

There was a syntax error in the example. It's odd since I've compiled and tested it in the past. I added usage instructions to the README now. The actual syntax extension is ppx_deriving_random.ppx, as I've reserved the top-level package name for a future runtime or runtime+ppx. The free_magma.ml example also needs ppx_deriving.show.

[paurkedal]

Also added the package that I had already promised in the readme. I'll try to get it into the official opam repo later, as standalone package or part of ppx_deriving [#1], after adding some suitable default random instance distributions.

[neojski]

Thanks, I can compile and run it now!

[paurkedal]

Great, and thanks for testing!

[neojski]

Maybe one last thing: how do I print the transformed source code? I'm again following the @whitequark's blog post but I don't really know how to run something similar to ocamlfind ppx_tools/rewriter ./ppx_getenv.native foo.ml.

[paurkedal]

I got the following stub which I used for debugging:

ocamlfind ocamlopt -g -dsource \
    -package ppx_deriving \
    -package ppx_deriving.show \
    -ppxopt ppx_deriving,../_build/ppx_deriving_random.cmxs $test

So, try to pass -dsource. Didn't find it in the relevant man pages, so I'm not sure from where I got it.

[neojski]

Thank you!

[whitequark]

@neojski Using -dsource is pretty much what I myself do. Jane Street's ppx_driver seems to make that easier if you'd like.

@paurkedal I generally put the ppx extension itself in the toplevel package (i.e. ppx_deriving_random and the runtime, if any, in a sub-package (i.e. ppx_deriving_random.runtime). Having two ppx's in the default package name is awkward... and if you ever want to do something non-ppx with the same codebase, I'd say just split it out into a different package (i.e. random).

[paurkedal]

@whitequark The ppx subpackage convention is something I took away from a discussion "META file standards for ppx extensions" on the ocaml list a few months ago. In particular, see the mail Dario Teixeira, posted 2015-04-09. Not sure how the practise will pan out, but I think it would be good to have the same kind of consistency as for camlp4 extensions. I could image a amendment of to the proposed practise, though, saying that if the package name starts with "ppx_", then the scheme in inverted.