Ppx Protocol Conv

Ppx protocol conv (de)serializers using deriving, which allows for pluggable (de)serializers. Api.

This page contains a simple overview of the provided functionality. More information is available in the wiki pages

Table of contents

1. Features
2. Examples
3. Drivers
4. Custom drivers
5. Not supported

Features

The ppx supports the following features:

• records
• recursive and non-recursive types
• variants
• polymorphic variants
• all primitive types (including nativeint)

The following drivers exist:

• Json which serializes to Yojson.Safe.t
• Jsonm which serializes to Ezjsonm.value
• Msgpack which serializes to Msgpck.t
• Yaml which serializes to Yaml.t
• Xml_light which serializes to Xml.xml list
• Xmlm which serializes to Ezxmlm.node

Examples

open Protocol_conv_json
type a = {
  x: int;
  y: string [@key "Y"]
  z: int list [@default [2;3]]
} [@@deriving protocol ~driver:(module Json)]

type b = A of int
       | B of int [@key "b"]
       | C
[@@deriving protocol ~driver:(module Json)]

will generate the functions:

val a_to_json: a -> Json.t
val a_of_json_exn: Json.t -> a
val a_of_json: Json.t -> (a, exn) result

val b_to_json: b -> Json.t
val b_of_json_exn: Json.t -> b
val b_of_json: Json.t -> (b, exn) result

a_to_json { x=42; y:"really"; z:[6;7] }

Evaluates to

[ "x", `Int 42; "Y", `String "really"; "z", `List [ `Int 6; `Int 7 ] ] (* Yojson.Safe.json *)

to_protocol deriver generates serialization of the type. of_protocol deriver generates deserialization of the type, while protocol deriver generates both serialization and deserialization functions.

Attributes

Record label names can be changed using [@key <string>]

Variant and polymorphic variant constructors names can be changed using the [@name <string>] attribute.

If a record field is not present in the input when deserializing, a default value can be assigned using [@default <expr>]. If the value to be serialized matches the default value, the field will be omitted (Some drivers allow disabling this functionality. Comparison uses polymorphic compare, so be careful.)

Signatures

The ppx also handles signatures, but disallows [@key ...], [@default ...] and [@name ...] because these do not impact signatures.

Drivers

Drivers specify concrete serialization and deserialization. Users of the library can elect to implement their own driver, see custom drivers, or use predefined drivers:

• Json which serializes to Yojson.Safe.t
• Jsonm which serializes to Ezjsonm.value
• Msgpack which serializes to Msgpck.t
• Yaml which serializes to Yaml.t
• Xml_light which serializes to Xml.xml list
• Xmlm which serializes to Ezxmlm.node

Custom drivers

It is easy to provide custom drivers by implementing the signature:

include Protocol_conv.Runtime.Driver with
  type t = ...

See the drivers directory for examples on how to implement new drivers. Submissions of new drivers are more than welcome.

Not supported

• Generalised algebraic datatypes
• Extensible types
• Extensible polymorphic variants

Unsupported type shapes are reported with location-aware PPX errors.