You might be interested in:
https://github.com/janestreet/ppx_variants_conv

Example:

$ utop
utop # #require "ppx_deriving";;
utop # #require "ppx_variants_conv";;
utop # #require "variantslib";;

type t = A of int | C of int * int [@@deriving variants];;
type t = A of int | C of int * int
val c : int -> int -> t = <fun>
val a : int -> t = <fun>                                                                            
module Variants :
  sig
    val c : (int -> int -> t) Variantslib.Variant.t
    val a : (int -> t) Variantslib.Variant.t
    val fold :
      init:'a ->
      a:('a -> (int -> t) Variantslib.Variant.t -> 'b) ->
      c:('b -> (int -> int -> t) Variantslib.Variant.t -> 'c) -> 'c
    val iter :
      a:((int -> t) Variantslib.Variant.t -> 'a) ->
      c:((int -> int -> t) Variantslib.Variant.t -> 'b) -> 'b
    val map :
      t ->
      a:((int -> t) Variantslib.Variant.t -> int -> 'a) ->
      c:((int -> int -> t) Variantslib.Variant.t -> int -> int -> 'a) -> 'a
    val descriptions : (string * int) list
  end

(I'm not quite sure why you have to do three #require statements manually. Related to this.)


> Does everybody use camlp4/p5/ppx to customize the syntax to his liking

Note that the community is moving to ppx based syntax extensions, and away from camlp4/5.

> 200k of code

Where do you see that much code? I only see 6000 lines of code.



On Fri, Nov 6, 2015 at 8:09 AM, Soegtrop, Michael <michael.soegtrop@intel.com> wrote:

Dear Gabriel,

 

thanks for the link, an interesting idea and discussion! And I see that maybe I should come over to Paris to participate ;-) I would agree with Alain Frisch’s final comment that whenever a pattern synonym is used in the RHS, there should be an explicit binder. This would either solve the “trouble” case or make the similarity to (x, x) obvious.

 

Best regards,

 

Michael

 

From: caml-list-request@inria.fr [mailto:caml-list-request@inria.fr] On Behalf Of Gabriel Scherer
Sent: Friday, November 06, 2015 1:34 PM
To: Soegtrop, Michael
Cc: Francois Berenger; caml-list@inria.fr
Subject: Re: [Caml-list] Newbie comment on constructor syntax

 

The use of camlp{4,5} to change OCaml syntax has always had extremely low adoption, with some very specific exceptions (notably the lwt-support syntax of the Ocsigen project). I suspect that this is due to the fact that integrating a new syntax extension to your project has historically caused more build-system and deployment trouble than people were willing to tolerate.

ppx extensions are not designed to allow extending the OCaml syntax, and in particular I think they are not a good fit for what you are looking for. It is a large part of their appeal: by being less flexible, they are simpler and more robust.

I personally believe that currified constructor syntax would be a better choice, and that using non-currified constructors is a historical mistake of SML/Caml. But I am also not convinced that efforts to change it today are worth the trouble, and prefer to concentrate on improving other parts of the OCaml ecosystem.

Another thing that was touched by your comments is the usefulness of user-defined patterns (pattern synonyms). I have conflicted opinions on the question of whether adding pattern synonyms would be a good thing, but described one aspect of a proposal that I like (but also highlights that the feature can be a source of implementation complexity) in
  http://gallium.inria.fr/blog/pattern-synonyms-as-expressions/

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