Re: [Caml-list] [ANN] ppx_overload : ppx for user definable SML style overloading

[Alain Frisch <alain@frisch.fr>]

On 10/13/2014 03:56 PM, Peter Zotov wrote:
> On 2014-10-13 17:49, Jun Furuse wrote:
>> Hi,
>>
>> I have OPAM-released ppx_overload, a ppx for user definable SML style
>> overloading.
>
> Hi,
>
> Great hack! I wanted to do something similar, but yours is much more
> elegant than what I had in mind.
>
> One note though:
>
>> Unfortunately this ppx trick does not work for the toplevel. It is
>> since OCaml toplevel
>> re-execute the ppx filter each time it gets a toplevel phrase. This
>> makes the ppx filter
>> hard to keep its state, in this case, the typing environment.
>
> In 4.02.1 the toplevel allows the ppx rewriter to save some state.
> See
> http://caml.inria.fr/cgi-bin/viewvc.cgi/ocaml/trunk/parsing/ast_mapper.mli?view=markup#l192.


And sedlex ( https://github.com/alainfrisch/sedlex ) illustrates one 
possible approach for storing the state.  Instead of marshaling in any 
form some kind of internal state, it simply stores fragments of 
parsetree (here, structure items) that impacted its internal state and 
simply replay them on later phrases.  (This is not very efficient, but 
for quick experiments in the toplevel, this is fine.)  I don't know if 
this technique would apply to ppx_overload.

-- Alain