Deserialise YAML Data using hl_yaml

Task

Data Formats / YAML / Deserialise YAML Data

Deserialise a YAML file whose structure maps to some OCaml types.

Opam Packages Used

  • hl_yaml Tested with version: 1.0.0 — Used libraries: hl_yaml
  • ppx_deriving_yojson Tested with version: 3.7.0 — Used libraries: ppx_deriving_yojson

Code

This is the string we are deserializing into the types we define below.

let yaml = {|
french name: pâte sucrée
ingredients:
- name: flour
  weight: 250
- name: butter
  weight: 100
- name: sugar
  weight: 100
- name: egg
  weight: 50
- name: salt
  weight: 5
steps:
- soften butter
- add sugar
- add egg and salt
- add flour
|}

The [@@deriving of_yojson] attribute makes the ppx from the library ppx_deriving_yojson generate the function ingredient_of_yojson : Yojson.Safe.t -> (ingredient, string) result. If both serialising and deserialising are needed, replace of_yojson by yojson.

type ingredient = {
  name: string;
  weight: int;
} [@@deriving of_yojson]

The function recipe_of_yojson : Yojson.Safe.t -> (ingredient, string) result generated here internally uses ingredient_of_yojson.

type recipe = {
  name: string; [@key "french name"]
  ingredients: ingredient list;
  steps: string list;
} [@@deriving of_yojson]

parse takes a function that converts from Yojson.Safe.t into the desired record type as an argument.

let pate_sucree =
  yaml
  |> Hl_yaml.Unix.parse ~of_yojson:recipe_of_yojson

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