[wg-camlp4] Raw representation of literals in the parsetree

[Gabriel Scherer]

I think it is very reasonable, and would be a good fit for Alain's branch.

On Thu, May 2, 2013 at 1:35 PM, Jeremie Dimino <jdimino at janestreet.com> wrote:
> Hi,
>
> We recently felt the need to write a new extension that would check
> integer literals.  The goal is to verify that ones containing
> underscores match a specific regular expression.  Namely digits are
> grouped by 3.
>
> We can do that for instance with a camlp4 token filter, but we wanted
> to try with ppx.  It is currently not possible to do it by looking at
> the parsetree since constants are already evaluated (integers are
> represented by an OCaml int) and the raw form is lost.
>
> One solution would be to add the raw representation of constants in
> the parsetree. For instance by changing Asttypes.constant to:
>
> ,----
> | type constant_value =
> |     Const_int of int
> |   | Const_char of char
> |   | Const_string of string
> |   | Const_float of string
> |   | Const_int32 of int32
> |   | Const_int64 of int64
> |   | Const_nativeint of nativeint
> |
> | type constant = constant_value * string
> `----
>
> I believe it could also be useful for other rewriters, especially ones
> dealing with strings since they would be able to compute the correct
> location inside a string. And maybe also for printing: Pprintast could
> use the representation choosed by the programmer instead of a
> standardized one.
>
> Do people thinks that this a reasonable thing to add to the OCaml
> parsetree? If yes I can do the modification.
>
> Jeremie
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