Re: [Caml-list] Conditional BuildDepends in OASIS

[Anil Madhavapeddy <anil@recoil.org>]

The Cohttp library generates sub-libraries which can be conditional
based on a flag (which has a portable functorised core, and then an
Async, Mirage or Lwt instance depending on what's available)
https://github.com/avsm/ocaml-cohttp/blob/master/_oasis

However, your use case seems a little different, as I presume the
external interface of pgocaml doesn't vary by your choice of Extlib
or Batteries?

Despite this, it might be easier just to define a "pgocaml.batteries"
and "pgocaml.extlib" and leave the choice with the user as to which
one they would like to select.  You can make the dependency optional
at compile time so the package doesn't generated; e.g.

Library cohttp_lwt_unix
  Build$: flag(lwt)
  Install$: flag(lwt)
  Path: lwt
  Findlibname: lwt
  FindlibParent: cohttp
  BuildDepends: lwt.unix, uri, cohttp, lwt.ssl, lwt.syntax
  Modules: Cohttp_lwt_unix, (etc...)


-anil

On 25 Oct 2012, at 06:57, Dario Teixeira <darioteixeira@yahoo.com> wrote:

> Hi,
> 
> I'm in the process of oasifying PG'OCaml, and I've hit a snag.
> By default PG'OCaml depends on ExtLib, but it's possible to
> use Batteries instead.  Below is a fragment of my (naïve) first
> attempt at telling OASIS about this configuration option:
> 
> 
> Flag "use_batteries"
>   Description: Use Batteries instead of ExtLib
>   Default: false
> 
> Library "pgocaml"
>   Path:                 src
>   Modules:              PGOCaml
>   BuildTools:           ocamlbuild, camlp4
>   BuildDepends:         calendar
>   if flag(use_batteries)
>     BuildDepends+:      batteries
>     ByteOpt+:           -ppopt -DUSE_BATTERIES
>     NativeOpt+:         -ppopt -DUSE_BATTERIES
>   else
>     BuildDepends+:      extlib
> 
> The problem is that OASIS complains about BuildDepends being
> 
> placed inside a conditional.  Is this an oversight, or are there good
> reasons (and hopefully a standard workaround) for this limitation?
> 
> Thanks in advance!
> Cheers,
> Dario Teixeira
> 
> 
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