Re: [Caml-list] concerning using of `deriving' syntactic plugin

["Matej Košík" <5764c029b688c1c0d24a2e97cd764f@gmail.com>]

Hi Markus,

On 03/07/2012 05:10 PM, Markus Mottl wrote:
> On Wed, Mar 7, 2012 at 11:44, Matej Košík
> <5764c029b688c1c0d24a2e97cd764f@gmail.com> wrote:
>> I have found one (I guess unnecessary) disadvantage over `deriving'.
>> If you process your *.ml file with sexplib/bin_prot preprocessor, you
>> have to append "with ..." suffix to every type definition, otherwise you
>> will get a an error report from the preprocessor. `Deriving' does not
>> force you to do that. You can annotate only those type definitions,
>> which for you makes sense to annotate.
> 
> I'm not sure what the perceived problem is, but there should be no
> need to annotate all type definitions.  It should suffice to annotate
> those for which converters are needed.

The following artificial example:

  open Sexplib.Conv
  type foo = int * int with sexp
  type bar = float * float with sexp

is compilable

  (e.g.:
   ocamlc -o main -pp "camlp4of -I
/home/mkosik/lib/godi/lib/ocaml/std-lib/../pkg-lib/sexplib -I
/home/mkosik/lib/godi/lib/ocaml/std-lib/../pkg-lib/type-conv
pa_type_conv.cma pa_sexp_conv.cma" -I
/home/mkosik/lib/godi/lib/ocaml/std-lib/../pkg-lib/sexplib -I
/home/mkosik/lib/godi/lib/ocaml/std-lib/../pkg-lib/type-conv unix.cma
nums.cma bigarray.cma sexplib.cma main.ml
  )

If you remove any of the "with sexp" clauses, you will get a
preprocessor error:

  File "main.ml", line 4, characters 18-23:
  Parse error: "with" expected after [type_declaration] (in [str_item])
  File "main.ml", line 1, characters 0-1:

This is at least what I am experiencing.

> This, of course, means that
> any types that a type definition is referring to will also need
> annotations (or hand-written conversion functions).

Regards,

Matej Kosik