JSON derivation

The js_of_ocaml-ppx_deriving_json package provides a PPX deriver for serializing OCaml values to JSON.

Important: The serialization format follows js_of_ocaml's internal representation. It is designed for communication between a js_of_ocaml program and a server-side OCaml application, not for interacting with third-party APIs.

Installation

opam install js_of_ocaml-ppx_deriving_json

Usage

Add [@@deriving json] to your type definitions:

type person = {
  name : string;
  age : int;
}
[@@deriving json]

(* Serialize to a JSON string *)
let json_str = Deriving_Json.to_string person_json { name = "Alice"; age = 30 }

(* Deserialize from a JSON string *)
let alice = Deriving_Json.from_string person_json json_str

The [@@deriving json] attribute generates:

• person_to_json : Buffer.t -> person -> unit — write a value to a buffer
• person_of_json : Deriving_Json_lexer.lexbuf -> person — read a value from a lexer buffer
• person_json : person Deriving_Json.t — a witness, usable with Deriving_Json.to_string and Deriving_Json.from_string for string conversion (as in the example above)

Note: For types named t, the prefix is omitted (e.g., of_json instead of t_of_json).

The [%to_json: type] and [%of_json: type] syntax also works with any type expression:

let json = [%to_json: int list] [1; 2; 3]
let nums = [%of_json: int list] json

Supported types

The deriver supports:

• Basic types: int, float, string, bool
• Options: 'a option
• Lists and arrays: 'a list, 'a array
• Records and variants
• Polymorphic variants
• Recursive types

See also

• JSON serialization — Direct JSON output