Hello,
how can I tell oasis that my syntax extension needs camlp4of instead of
camlp4o ? I tried to add a ByteOpt line for this:

Library pa_guizmin
  Path:               src/syntax
  Modules:            Pa_guizmin
  FindlibParent:      guizmin
  FindlibName:        syntax
  BuildDepends:       camlp4.lib, camlp4.quotations.o
  CompiledObject:     byte
  ByteOpt:            -pp camlp4of

and indeed myocamlbuild.ml now contains:

let package_default =
  {
     MyOCamlbuildBase.lib_ocaml =
       [("src/syntax/pa_guizmin", ["src/syntax"]); ("src/guizmin",
["src"])];
     lib_c = [];
     flags =
       [
          (["oasis_library_pa_guizmin_byte"; "ocaml"; "link"; "byte"],
            [(OASISExpr.EBool true, S [A "-pp"; A "camlp4of"])]);
          (["oasis_library_pa_guizmin_byte"; "ocaml"; "ocamldep"; "byte"],
            [(OASISExpr.EBool true, S [A "-pp"; A "camlp4of"])]);
          (["oasis_library_pa_guizmin_byte"; "ocaml"; "compile"; "byte"],
            [(OASISExpr.EBool true, S [A "-pp"; A "camlp4of"])])
       ];
     }
  ;;

But still, these options are not used when I compile using ocaml setup.ml-build

+ ocamlfind ocamldep -package camlp4.quotations.o -package camlp4.lib
-package camlp4.extend -modules src/syntax/pa_guizmin.ml >
src/syntax/pa_guizmin.ml.depends
File "src/syntax/pa_guizmin.ml", line 22, characters 3-5:
Error: Syntax error

Am I missing something ?

Cheers,
  Philippe.