Tl;DR

TL;DR

install the package through opam:

opam install ppx_protocol_conv_json

Create a dune file with the contents:

(executable
 (name        test)
 (modules     test)
 (libraries   ppx_protocol_conv_json yojson)
 (preprocess (pps ppx_protocol_conv)))

And a test.ml file with the contents:

open Protocol_conv_json
type t = A of int | B of float
[@@deriving protocol ~driver:(module Json)]

let () = 
  let t = A 5
  let json = to_json t in
  Printf.printf "t serialized: %s\n" (Yojson.Safe.to_string json);
  let t' = of_json json in
  print_endline "Done!"

The above example uses the Json driver to serialize / deserialize The following drivers are provided:

• json
• jsonm
• yaml
• msgpack
• xml_light