How to use Fieldslib and ppx_fields_conv with OCaml 4.06.1?

[RogerTarani]

RWO 2nd Edition promotes the use of Fieldslib (and ppx_fields_conv, depending both on ppxlib).
See First-Class Fields.

I can't generate the record helpers.
How to make Fieldslib and ppx_fields_conv working?

I'm using OCaml 4.06.1 and the required packages are installed:

$ opam list
fieldslib                   v0.11.0  Syntax extension to define first class valu
...
ppx_fields_conv          v0.11.0  Generation of accessor and iteration functi
ppxlib                        0.2.1  A comprehensive toolbox for ppx development

As well as "base" v0.11.0, "jbuilder" 1.0+beta20 (req. build & >= "1.0+beta18.1"} and "ocaml-migrate-parsetree" 1.0.11 (req. >= "1.0") required by these three packages (fieldslib, ppx_fields_conv, ppxlib).

Unfortunately, when trying the example of the book with utop, I don't get the expected output (all the helpers) triggered by [@@deriving fields]:

# module Logon = struct
  type t =
    { session_id: string;
      time: Time_ns.t;
      user: string;
     credentials: string;
    }
  [@@deriving fields]
end;;
module Logon :
  sig
    type t = {
      session_id : string;
      time : Time_ns.t;
      user : string;
      credentials : string;
    }
  end

I tried unsuccessfully:

# #require "fieldslib";;
# open Fieldslib;;

and other rather random directives and commands.

What are the instructions for using Fieldslib (and ppx_fields_conv as well)?

PS : which OCaml tooling configuration (OCaml version, libraries version, jbuilder and related tools, etc. MUST be used to reliably and comfortably study RWO 2nd Edition?
e.g. I note that odoc, odig, ocaml-manual is a useful set of packages for generating module documentation, but ocaml-manual requires ocaml-version >= "4.05.0" & ocaml-version < "4.06.0".
So I if switch to 4.05.x, is there another lurking version conflict that may arise?...

Thanks

[yminsky]

Try:

#require "ppx_jane";;
open Base

You can also use the narrower #require "ppx_fields_conv", but the broader import will work for a bunch of other features explored by RWO.

[yminsky]

Also, the instructions here on how to set up your .ocamlinit file will get your utop set up properly:

https://dev.realworldocaml.org/install.html

[RogerTarani]

The following directive worked immediately for me:

#require "ppx_jane"

Then he helpers code was generated:

# module Logon = struct
  type t =
    { session_id: string;
      time: Time_ns.t;
      user: string;
     credentials: string;
    }
  [@@deriving fields]
end;;
module Logon :
  sig
    type t = {
      session_id : string;
      time : Time_ns.t;
      user : string;
      credentials : string;
    }
    val credentials : t -> string
    val user : t -> string
    val time : t -> Time_ns.t
    val session_id : t -> string
    module Fields :
      sig
      (...)
            val set_all_mutable_fields : 'a -> unit
          end
      end
  end

Whereas the following was not enough:

# #require "ppx_fields_conv";;
No such package: ppx_deriving - required by `ppx_fields_conv'

Do you know what is still necessary to only load ppx_fields_conv?

FYI, my ~/.ocamlinit is compliant to your recommendations:

$ cat ~/.ocamlinit
(* ## added by OPAM user-setup for ocamltop / base ## 3ec62baf6f9c219ae06d98140$
#use "topfind";;
(* ## end of OPAM user-setup addition for ocamltop / base ## keep this line *)
#thread;;
#require "core.top";;
#require "core.syntax";;
open Core

Thanks.

[yminsky]

Not offhand. This seems like an issue to raise against https://github.com/janestreet/ppx_fields_conv

[RogerTarani]

Thanks. Done:
janestreet/ppx_fields_conv#2
I'll update and close the present issue when we get the answer.

[NathanReb]

Any update on this? I assume this can be closed but feel free to ping me if you want it re-opened!

[vitaliel]

Maybe we need to put #require "ppx_jane";; on page
https://dev.realworldocaml.org/records.html

Without it [@@deriving fields] does not work in below snippet and user should search the web.

  type t =
    { session_id: string;
      time: Time_ns.t;
      user: string;
      credentials: string;
    }
  [@@deriving fields]
end
;;