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IDProjectCategoryView StatusDate SubmittedLast Update
0006135OCamlOCaml documentationpublic2013-08-22 11:232014-09-04 00:25
ReporterHendrik Tews 
Assigned Togasche 
PlatformOSOS Version
Product Version4.01.0+beta/+rc 
Target VersionundecidedFixed in Version 
Summary0006135: Please document -ppx option
DescriptionLooking at the 4.01beta reference manual I cannot find -ppx!

Apart from including -ppx it would be nice to have some basic information about ppx commands (howto read/write the syntax tree, the type of the syntax tree), as well as a pointer to more extensive documentation.
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gasche (developer)
2013-08-22 11:36

My personal hunch is that before we know what will be done with extension_points branch (eg. integrating it in time for a 4.02 release), there are relatively few legitimate uses of -ppx, and adding extension_points in the mix would probably require an extensive reformulation of the documentation if it exists. (There already is some documentation for extension_points specifically in [^] ).

In particular, I think that using -ppx to overload the meaning of program fragments that already have a syntactic meaning in the existing OCaml language (as done in wmeyer's OMonad for experimentation purposes : [^] ) is a bad practice that we should not encourage. The question is what other use cases remain without extension_points. There are definitely some ( it is used by an experimental version of Bisect [^] for example), but not as much as there could be in 4.02.

Of course more documentation is better than less, so if you or anyone feels motivated to write something (I guess the best thing to do for now is to look at the existing uses of -ppx to understand how to implement filters with it), I would be happy to have a look, provide feedback, and get something integrated in the manual if it's good.
doligez (administrator)
2013-08-22 21:47

Hmm. I spend a whole day making sure that every command line option is documented, both in the manual and in the man pages, for ocamlc, ocamlopt, and ocaml...

As for giving a detailed documentation of the AST types, I think like Gabriel that it's probably too early.
Hendrik Tews (reporter)
2013-08-23 11:43

OK, I didn't know that the extensions have not been merged yet.

Then I would suggest to briefly document -ppx with the calling convention and the data type, eg

-ppx <command> Run <command> as external filter on the
                  abstract syntax tree after parsing. The filter
                  is expected to read/write a marshaled ast
                  of type XXX on stdin/stdout. This option will
                  only get useful when extension points have been
                  implemented in one of the following releases.
shinwell (developer)
2014-08-20 09:48

Gabriel, what are we going to do about this? It's marked as target 4.02.0+dev.
doligez (administrator)
2014-08-20 19:09

> It's marked as target 4.02.0+dev.

That doesn't mean it must be done for 4.02.0, we can still postpone it. I talked to Alain in private, and he says we can (and should) document it after the release.
gasche (developer)
2014-08-21 08:37
edited on: 2014-08-21 08:37

I don't know -ppx well enough to write the documentation (should I reassign the issue?). If Alain can do it, that's very good; otherwise we may try to nicely ask Peter "whitequark" Zotov for help, as he's played with -ppx a lot in the last few months.

doligez (administrator)
2014-08-21 11:16

Alain is busy right now, so I'll release 4.02 without this documentation. It's still urgent but it can be written after the release.

- Issue History
Date Modified Username Field Change
2013-08-22 11:23 Hendrik Tews New Issue
2013-08-22 11:36 gasche Note Added: 0010226
2013-08-22 21:47 doligez Note Added: 0010227
2013-08-22 21:47 doligez Status new => acknowledged
2013-08-22 21:47 doligez Target Version => later
2013-08-23 11:43 Hendrik Tews Note Added: 0010235
2013-09-12 15:59 doligez Target Version later => 4.02.0+dev
2014-08-18 20:20 doligez Priority normal => urgent
2014-08-20 09:48 shinwell Note Added: 0012027
2014-08-20 09:48 shinwell Assigned To => gasche
2014-08-20 09:48 shinwell Status acknowledged => assigned
2014-08-20 19:09 doligez Note Added: 0012030
2014-08-21 08:37 gasche Note Added: 0012036
2014-08-21 08:37 gasche Note Edited: 0012036 View Revisions
2014-08-21 11:16 doligez Note Added: 0012038
2014-08-21 11:16 doligez Target Version 4.02.0+dev => 4.02.1+dev
2014-09-04 00:25 doligez Target Version 4.02.1+dev => undecided

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