Hi Xavier,

Bisect_ppx does this by looking at the location of each module it sees in “structure". The file names are stored in a set. If a file name is not yet in the set, Bisect_ppx assumes that the module is the top-level module of a file. We haven’t had any problems with it.

You can see it here: https://github.com/aantron/bisect_ppx/blob/afa95d9f02ab4c95df3af283641c73ec1dc8cfb1/src/syntax/instrumentPpx.ml#L480 <https://github.com/aantron/bisect_ppx/blob/afa95d9f02ab4c95df3af283641c73ec1dc8cfb1/src/syntax/instrumentPpx.ml#L480>

The code is a bit old, but there it is.

Best,
Anton

> On Jun 17, 2016, at 12:10, Xavier Van de Woestyne <xavier@derniercri.io> wrote:
> 
> Hello, 
> I have writted some ppx extension but I have a question, 
> Is there a proper way to add a start "file" structure.
> I have try using the "structure" member of the mapper : 
> 
> `
> let new_mapper =
>  Ast_mapper.{
>    default_mapper with
>    structure = general_structure
>  }`
> 
> Where general_structure is just a
> `my_begining_structure :: List.map (...)` but my begining 
> structure is repeated into each module. It is logic but I need 
> to add my own structure only at the begining of my file. In an 
> other project, I use a mandatory attribute ([@@@active_this_ppx] 
> for example), but imho, it is not a good approach. 
> 
> Thanks a lot for your feedback and advices ! 
> 
> Xavier Van de Woestyne
> Développeur à Derniercri.io
> http://derniercri.io
>