Deriving-yojson

Deriving-yojson is a Deriving (https://github.com/ocsigen/deriving) extention to print / parse ocaml value to / from json. Json manipulation is done by Yojson (https://github.com/mjambon/yojson/)

Exemple

type location = {
  lat : float;
  lon : float;
} deriving (Yojson)

type t = {
  name : string;
  loc : location option
} deriving (Yojson)

Parsing

let value_from_json = Yojson_t.from_json ?o json
let value_from_string = Yojson_t.from_string ?o string

The parameter o is an optionnal default value. If the json is incomplete, this default value will provide a value for missing fields

let value_from_string = Yojson_t.from_string
    ~o:{name="name";loc=None} "{\"loc\":{\"lat\": 5.2, \"lon\": 9.4}}"

Printing

let s = Yojson_t.to_string ?filter t

the optionnal parameter filter allow to filter the output.

let s = Yojson_t.to_string ~filter:[["loc";"some";"lat"];["name"]] value_from_string

will ouput

{"name":"name","loc":{"lat":5.2}}