atdgen
Biniou and JSON serialization for OCaml
release 1.0.0

Martin Jambon
© 2010 MyLife

Contents

1  Introduction

Atdgen is a command-line program that takes as input type definitions in the ATD syntax and produces OCaml code suitable for data serialization and deserialization.

Two data formats are currently supported, these are biniou and JSON. Atdgen-biniou and atdgen-json will refer to atdgen used in one context or the other.

Atdgen was designed with efficiency and durability in mind. Software authors are encouraged to use atdgen directly and to write tools that may reuse part of atdgen's source code.

Atdgen depends heavily on the following packages:

2  Command-line usage

2.1  Command-line help

$ atdgen -help
Generate OCaml serializers and deserializers.
Default serialization format is biniou.
Usage: ./atdgen FILE.atd
  -open Module1,Module2,...
          List of modules to open (comma-separated or space-separated)
  -ntd 
          Do not dump OCaml type definitions
  -nfd 
          Do not dump OCaml function definitions
  -rec 
          Keep OCaml type definitions mutually recursive
  -o PREFIX
          Use this prefix for the generated files, e.g. 'foo/bar' for
          foo/bar.ml and foo/bar.mli
  -biniou 
          Write serializers and deserializers for Biniou (default).
  -json 
          Write serializers and deserializers for JSON.
  -std-json 
          Convert tuples and variants into standard JSON and
          refuse to print NaN and infinities (implying -json).
  -version 
          Print the version identifier of atdgen and exit.
  -help  Display this list of options
  --help  Display this list of options

2.2  Atdgen-biniou example

$ atdgen -biniou example.atd
Input file example.atd:
type profile = {
  id : string;
  email : string;
  ~email_validated : bool;
  name : string;
  ?real_name : string option;
  ~about_me : string list;
  ?gender : gender option;
  ?date_of_birth : date option;
}

type gender = [ Female | Male ]

type date = {
  year : int;
  month : int;
  day : int;
}
produces the interface file example.mli and the implementation file example.ml. This is example.mli:
(* Auto-generated from "example.atd" *)


type date = { year: int; month: int; day: int }

type gender = [ `Female | `Male ]

type profile = {
  id: string;
  email: string;
  email_validated: bool;
  name: string;
  real_name: string option;
  about_me: string list;
  gender: gender option;
  date_of_birth: date option
}

(* Writers for type date *)

val date_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!date}.
      Readers may support more than just this tag. *)

val write_untagged_date :
  Bi_outbuf.t -> date -> unit
  (** Output an untagged biniou value of type {!date}. *)

val write_date :
  Bi_outbuf.t -> date -> unit
  (** Output a biniou value of type {!date}. *)

val string_of_date :
  int -> date -> string
  (** Serialize a value of type {!date} into 
      a biniou string. *)

(* Readers for type date *)

val get_date_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> date)
  (** Return a function that reads an untagged
      biniou value of type {!date}. *)

val read_date :
  Bi_inbuf.t -> date
  (** Input a tagged biniou value of type {!date}. *)

val date_of_string :
  ?pos:int -> string -> date
  (** Deserialize a biniou value of type {!date}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_date :
  year: int ->
  month: int ->
  day: int ->
  unit -> date
  (** Create a record of type {!date}. *)


(* Writers for type gender *)

val gender_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!gender}.
      Readers may support more than just this tag. *)

val write_untagged_gender :
  Bi_outbuf.t -> gender -> unit
  (** Output an untagged biniou value of type {!gender}. *)

val write_gender :
  Bi_outbuf.t -> gender -> unit
  (** Output a biniou value of type {!gender}. *)

val string_of_gender :
  int -> gender -> string
  (** Serialize a value of type {!gender} into 
      a biniou string. *)

(* Readers for type gender *)

val get_gender_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> gender)
  (** Return a function that reads an untagged
      biniou value of type {!gender}. *)

val read_gender :
  Bi_inbuf.t -> gender
  (** Input a tagged biniou value of type {!gender}. *)

val gender_of_string :
  ?pos:int -> string -> gender
  (** Deserialize a biniou value of type {!gender}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)


(* Writers for type profile *)

val profile_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!profile}.
      Readers may support more than just this tag. *)

val write_untagged_profile :
  Bi_outbuf.t -> profile -> unit
  (** Output an untagged biniou value of type {!profile}. *)

val write_profile :
  Bi_outbuf.t -> profile -> unit
  (** Output a biniou value of type {!profile}. *)

val string_of_profile :
  int -> profile -> string
  (** Serialize a value of type {!profile} into 
      a biniou string. *)

(* Readers for type profile *)

val get_profile_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> profile)
  (** Return a function that reads an untagged
      biniou value of type {!profile}. *)

val read_profile :
  Bi_inbuf.t -> profile
  (** Input a tagged biniou value of type {!profile}. *)

val profile_of_string :
  ?pos:int -> string -> profile
  (** Deserialize a biniou value of type {!profile}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_profile :
  id: string ->
  email: string ->
  ?email_validated: bool ->
  name: string ->
  ?real_name: string ->
  ?about_me: string list ->
  ?gender: gender ->
  ?date_of_birth: date ->
  unit -> profile
  (** Create a record of type {!profile}. *)


2.3  Atdgen-json example

$ atdgen -json example.atd
Input file example.atd:
type profile = {
  id : string;
  email : string;
  ~email_validated : bool;
  name : string;
  ?real_name : string option;
  ~about_me : string list;
  ?gender : gender option;
  ?date_of_birth : date option;
}

type gender = [ Female | Male ]

type date = {
  year : int;
  month : int;
  day : int;
}
produces the interface file example.mli and the implementation file example.ml. This is example.mli:
(* Auto-generated from "example.atd" *)


type date = { year: int; month: int; day: int }

type gender = [ `Female | `Male ]

type profile = {
  id: string;
  email: string;
  email_validated: bool;
  name: string;
  real_name: string option;
  about_me: string list;
  gender: gender option;
  date_of_birth: date option
}

val write_date :
  Bi_outbuf.t -> date -> unit
  (** Output a JSON value of type {!date}. *)

val string_of_date :
  ?len:int -> date -> string
  (** Serialize a value of type {!date}
      into a JSON string.
      @param len specifies the initial length 
                 of the buffer used internally.
                 Default: 1024. *)

val read_date :
  Yojson.Safe.lexer_state -> Lexing.lexbuf -> date
  (** Input JSON data of type {!date}. *)

val date_of_string :
  string -> date
  (** Deserialize JSON data of type {!date}. *)

val create_date :
  year: int ->
  month: int ->
  day: int ->
  unit -> date
  (** Create a record of type {!date}. *)


val write_gender :
  Bi_outbuf.t -> gender -> unit
  (** Output a JSON value of type {!gender}. *)

val string_of_gender :
  ?len:int -> gender -> string
  (** Serialize a value of type {!gender}
      into a JSON string.
      @param len specifies the initial length 
                 of the buffer used internally.
                 Default: 1024. *)

val read_gender :
  Yojson.Safe.lexer_state -> Lexing.lexbuf -> gender
  (** Input JSON data of type {!gender}. *)

val gender_of_string :
  string -> gender
  (** Deserialize JSON data of type {!gender}. *)


val write_profile :
  Bi_outbuf.t -> profile -> unit
  (** Output a JSON value of type {!profile}. *)

val string_of_profile :
  ?len:int -> profile -> string
  (** Serialize a value of type {!profile}
      into a JSON string.
      @param len specifies the initial length 
                 of the buffer used internally.
                 Default: 1024. *)

val read_profile :
  Yojson.Safe.lexer_state -> Lexing.lexbuf -> profile
  (** Input JSON data of type {!profile}. *)

val profile_of_string :
  string -> profile
  (** Deserialize JSON data of type {!profile}. *)

val create_profile :
  id: string ->
  email: string ->
  ?email_validated: bool ->
  name: string ->
  ?real_name: string ->
  ?about_me: string list ->
  ?gender: gender ->
  ?date_of_birth: date ->
  unit -> profile
  (** Create a record of type {!profile}. *)


3  Default mapping

The following table summarizes the default mapping between ATD types and OCaml, biniou and JSON data types. For each language more representations are available and are detailed in the next section of this manual.
ATD OCaml Biniou JSON
unit unit unit null
bool bool bool boolean
int int svint number (int)
float float float64 number (not int)
string string string string
option option numeric variants (tag 0) None/Some variants
list list array array
variants polymorphic variants regular variants variants
record record record object
tuple tuple tuple tuple

Notes:

4  ATD Annotations

4.1  Section biniou

4.1.1  Field biniou.repr

Integers
Position: after int type

Values: svint (default), uvint, int8, int16, int32, int64

Semantics: specifies an alternate type for representing integers. The default type is svint. The other integers types provided by biniou are supported by atdgen-biniou. They have to map to the corresponding OCaml types in accordance with the following table:
Biniou type Supported OCaml type OCaml value range
svint int min_int ... max_int
uvint int 0 ... max_int, min_int ... -1
int8 char '\000' ... '\255'
int16 int 0 ... 65535
int32 int32 Int32.min_int ... Int32.max_int
int64 int64 Int64.min_int ... Int64.max_int

In addition to the mapping above, if the OCaml type is int, any biniou integer type can be read into OCaml data regardless of the declared biniou type.

Example:
type t = {
  id : int
    <ocaml repr="int64">
    <biniou repr="int64">;
  data : string list;
}
Arrays and tables
Position: applies to lists of records

Values: array (default), table

Semantics: table uses biniou's table format instead of a regular array for serializing OCaml data into biniou. Both formats are supported for reading into OCaml data regardless of the annotation. The table format allows

Example:
type item = {
  id : int;
  data : string list;
}

type items = item list <biniou repr="table">

4.2  Section json

4.2.1  Field json.name

Position: after field name or variant name

Values: any string making a valid JSON string value

Semantics: specifies an alternate object field name or variant name to be used by the JSON representation.

Example:
type color = [
    Black <json name="black">
  | White <json name="white">
  | Grey <json name="grey">
]

type profile = {
  id <json name="ID"> : int;
  username : string;
  background_color : color;
}
A valid JSON object of the profile type above is:
{
  "ID": 12345678,
  "username": "kimforever",
  "background_color": "black"
}

4.3  Section ocaml

4.3.1  Field ocaml.predef

Position: left-hand side of a type definition, after the type name

Values: none, true or false

Semantics: this flag indicates that the corresponding OCaml type definition must be omitted.

Example:
(* Some third-party OCaml code *)
type message = {
  from : string;
  subject : string;
  body : string;
}
(*
   Our own ATD file used for making message_of_string and
   string_of_message functions.
*)
type message <ocaml predef> = {
  from : string;
  subject : string;
  body : string;
}

4.3.2  Field ocaml.mutable

Position: after a record field name

Values: none, true or false

Semantics: this flag indicates that the corresponding OCaml record field is mutable.

Example:
type counter = {
  total <ocaml mutable> : int;
  errors <ocaml mutable> : int;
}
translates to the following OCaml definition:
type counter = {
  mutable total : int;
  mutable errors : int;
}

4.3.3  Field ocaml.default

Position: after a record field name marked with a ~ symbol or at the beginning of a tuple field.

Values: any valid OCaml expression

Semantics: specifies an explicit default value for a field of an OCaml record or tuple, allowing that field to be omitted.

Example:
type color = [ Black | White | Rgb of (int * int * int) ]

type ford_t = {
  year : int;
  ~color <ocaml default="`Black"> : color;
}

type point = (int * int * <ocaml default="0"> : int)

4.3.4  Field ocaml.field_prefix

Position: record type expression

Values: any string making a valid prefix for OCaml record field names

Semantics: specifies a prefix to be prepended to each field of the OCaml definition of the record. Overridden by alternate field names defined on a per-field basis.

Example:
type point2 = {
  x : int;
  y : int;
} <ocaml field_prefix="p2_">
gives the following OCaml type definition:
type point2 = {
  p2_x : int;
  p2_y : int;
}

4.3.5  Field ocaml.name

Position: after record field name or variant name

Values: any string making a valid OCaml record field name or variant name

Semantics: specifies an alternate record field name or variant names to be used in OCaml.

Example:
type color = [
    Black <ocaml name="Grey0">
  | White <ocaml name="Grey100">
  | Grey <ocaml name="Grey50">
]

type profile = {
  id <ocaml name="profile_id"> : int;
  username : string;
}
gives the following OCaml type definitions:
type color = [
    `Grey0
  | `Grey100
  | `Grey50
]

type profile = {
  profile_id : int;
  username : string;
}

4.3.6  Field ocaml.repr

Integers
Position: after int type

Values: char, int32, int64

Semantics: specifies an alternate type for representing integers. The default type is int, but char, int32 and int64 can be used instead. These three types are supported by both atdgen-biniou and atdgen-json but atdgen-biniou currently requires that they map to the corresponding fixed-width types provided by the biniou format.

Example:
type t = {
  id : int
    <ocaml repr="int64">
    <biniou repr="int64">;
  data : string list;
}
Lists and arrays
Position: after list type

Values: array

Semantics: maps to OCaml's array type instead of list.

Example:
type t = {
  id : int;
  data : string list
    <ocaml repr="array">;
}
Sum types
Position: after a sum type (denoted by square brackets)

Values: classic

Semantics: maps to OCaml's classic variants instead of polymorphic variants.

Example:
type fruit = [ Apple | Orange ] <ocaml repr="classic">
translates to the following OCaml type definition:
type fruit = Apple | Orange

4.4  Section doc

Unlike comments, doc annotations are meant to be propagated into the generated source code. This is useful for making generated interface files readable without having to consult the original ATD file.

Generated source code comments can comply to a standard format and take advantage of documentation generators such as javadoc or ocamldoc.

4.4.1  Field doc.text

Position: Values: UTF-8-encoded text using a minimalistic markup language

Semantics: The markup language is defined as follows: Example: The following is a full example demonstrating the use of doc annotations but also shows the full interface file genealogy.mli generated using:
$ atdgen -biniou genealogy.atd
Input file genealogy.atd:
<doc text="Type definitions for family trees">

type tree = {
  members : person list;
  filiations : filiation list;
}

type filiation = {
  parent : person_id;
  child : person_id;
  filiation_type : filiation_type;
}
  <doc text="Connection between parent or primary caretaker and child">

type filiation_type = {
  ?genetic : bool option;
  ?pregnancy : bool option;
  ?raised_from_birth : bool option;
  ?raised : bool option;
  ?stepchild : bool option;
  ?adopted : bool option;
}
  <doc text="
Example of a father who raised his child from birth
but may not be the biological father:

{{{
{
  genetic = None;
  pregnancy = Some false;
  raised_from_birth = Some true;
  raised = Some true;
  stepchild = Some false;
  adopted = Some false;
}
}}}
">

type person_id
  <doc text="Two persons with the same {{person_id}} must be the same
             person. Two persons with different {{person_id}}s
             may be the same person if there is not enough evidence to
             support it."> = int

type person = {
  person_id : person_id;
  name : string;
  ~gender : gender list;
  ?biological_gender
    <doc text="Biological gender actually used for procreating"> :
    gender option;
}

type gender =
  [
  | F <doc text="female">
  | M <doc text="male">
  ]
    <doc text="Gender, definition depending on the context">
translates using atdgen -biniou genealogy.atd into the following OCaml interface file genealogy.mli with ocamldoc-compliant comments:
(* Auto-generated from "genealogy.atd" *)


(** Type definitions for family trees *)

(**
  Example of a father who raised his child from birth but may not be the
  biological father:
  
{v
\{
  genetic = None;
  pregnancy = Some false;
  raised_from_birth = Some true;
  raised = Some true;
  stepchild = Some false;
  adopted = Some false;
\}
v}
*)
type filiation_type = {
  genetic: bool option;
  pregnancy: bool option;
  raised_from_birth: bool option;
  raised: bool option;
  stepchild: bool option;
  adopted: bool option
}

(**
  Two persons with the same [person_id] must be the same person. Two persons
  with different [person_id]s may be the same person if there is not enough
  evidence to support it.
*)
type person_id = int

(** Connection between parent or primary caretaker and child *)
type filiation = {
  parent: person_id;
  child: person_id;
  filiation_type: filiation_type
}

(** Gender, definition depending on the context *)
type gender = [ `F (** female *) | `M (** male *) ]

type person = {
  person_id: person_id;
  name: string;
  gender: gender list;
  biological_gender: gender option
    (** Biological gender actually used for procreating *)
}

type tree = { members: person list; filiations: filiation list }

(* Writers for type filiation_type *)

val filiation_type_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!filiation_type}.
      Readers may support more than just this tag. *)

val write_untagged_filiation_type :
  Bi_outbuf.t -> filiation_type -> unit
  (** Output an untagged biniou value of type {!filiation_type}. *)

val write_filiation_type :
  Bi_outbuf.t -> filiation_type -> unit
  (** Output a biniou value of type {!filiation_type}. *)

val string_of_filiation_type :
  int -> filiation_type -> string
  (** Serialize a value of type {!filiation_type} into 
      a biniou string. *)

(* Readers for type filiation_type *)

val get_filiation_type_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> filiation_type)
  (** Return a function that reads an untagged
      biniou value of type {!filiation_type}. *)

val read_filiation_type :
  Bi_inbuf.t -> filiation_type
  (** Input a tagged biniou value of type {!filiation_type}. *)

val filiation_type_of_string :
  ?pos:int -> string -> filiation_type
  (** Deserialize a biniou value of type {!filiation_type}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_filiation_type :
  ?genetic: bool ->
  ?pregnancy: bool ->
  ?raised_from_birth: bool ->
  ?raised: bool ->
  ?stepchild: bool ->
  ?adopted: bool ->
  unit -> filiation_type
  (** Create a record of type {!filiation_type}. *)


(* Writers for type person_id *)

val person_id_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!person_id}.
      Readers may support more than just this tag. *)

val write_untagged_person_id :
  Bi_outbuf.t -> person_id -> unit
  (** Output an untagged biniou value of type {!person_id}. *)

val write_person_id :
  Bi_outbuf.t -> person_id -> unit
  (** Output a biniou value of type {!person_id}. *)

val string_of_person_id :
  int -> person_id -> string
  (** Serialize a value of type {!person_id} into 
      a biniou string. *)

(* Readers for type person_id *)

val get_person_id_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> person_id)
  (** Return a function that reads an untagged
      biniou value of type {!person_id}. *)

val read_person_id :
  Bi_inbuf.t -> person_id
  (** Input a tagged biniou value of type {!person_id}. *)

val person_id_of_string :
  ?pos:int -> string -> person_id
  (** Deserialize a biniou value of type {!person_id}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)


(* Writers for type filiation *)

val filiation_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!filiation}.
      Readers may support more than just this tag. *)

val write_untagged_filiation :
  Bi_outbuf.t -> filiation -> unit
  (** Output an untagged biniou value of type {!filiation}. *)

val write_filiation :
  Bi_outbuf.t -> filiation -> unit
  (** Output a biniou value of type {!filiation}. *)

val string_of_filiation :
  int -> filiation -> string
  (** Serialize a value of type {!filiation} into 
      a biniou string. *)

(* Readers for type filiation *)

val get_filiation_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> filiation)
  (** Return a function that reads an untagged
      biniou value of type {!filiation}. *)

val read_filiation :
  Bi_inbuf.t -> filiation
  (** Input a tagged biniou value of type {!filiation}. *)

val filiation_of_string :
  ?pos:int -> string -> filiation
  (** Deserialize a biniou value of type {!filiation}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_filiation :
  parent: person_id ->
  child: person_id ->
  filiation_type: filiation_type ->
  unit -> filiation
  (** Create a record of type {!filiation}. *)


(* Writers for type gender *)

val gender_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!gender}.
      Readers may support more than just this tag. *)

val write_untagged_gender :
  Bi_outbuf.t -> gender -> unit
  (** Output an untagged biniou value of type {!gender}. *)

val write_gender :
  Bi_outbuf.t -> gender -> unit
  (** Output a biniou value of type {!gender}. *)

val string_of_gender :
  int -> gender -> string
  (** Serialize a value of type {!gender} into 
      a biniou string. *)

(* Readers for type gender *)

val get_gender_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> gender)
  (** Return a function that reads an untagged
      biniou value of type {!gender}. *)

val read_gender :
  Bi_inbuf.t -> gender
  (** Input a tagged biniou value of type {!gender}. *)

val gender_of_string :
  ?pos:int -> string -> gender
  (** Deserialize a biniou value of type {!gender}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)


(* Writers for type person *)

val person_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!person}.
      Readers may support more than just this tag. *)

val write_untagged_person :
  Bi_outbuf.t -> person -> unit
  (** Output an untagged biniou value of type {!person}. *)

val write_person :
  Bi_outbuf.t -> person -> unit
  (** Output a biniou value of type {!person}. *)

val string_of_person :
  int -> person -> string
  (** Serialize a value of type {!person} into 
      a biniou string. *)

(* Readers for type person *)

val get_person_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> person)
  (** Return a function that reads an untagged
      biniou value of type {!person}. *)

val read_person :
  Bi_inbuf.t -> person
  (** Input a tagged biniou value of type {!person}. *)

val person_of_string :
  ?pos:int -> string -> person
  (** Deserialize a biniou value of type {!person}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_person :
  person_id: person_id ->
  name: string ->
  ?gender: gender list ->
  ?biological_gender: gender ->
  unit -> person
  (** Create a record of type {!person}. *)


(* Writers for type tree *)

val tree_tag : Bi_io.node_tag
  (** Tag used by the writers for type {!tree}.
      Readers may support more than just this tag. *)

val write_untagged_tree :
  Bi_outbuf.t -> tree -> unit
  (** Output an untagged biniou value of type {!tree}. *)

val write_tree :
  Bi_outbuf.t -> tree -> unit
  (** Output a biniou value of type {!tree}. *)

val string_of_tree :
  int -> tree -> string
  (** Serialize a value of type {!tree} into 
      a biniou string. *)

(* Readers for type tree *)

val get_tree_reader :
  Bi_io.node_tag -> (Bi_inbuf.t -> tree)
  (** Return a function that reads an untagged
      biniou value of type {!tree}. *)

val read_tree :
  Bi_inbuf.t -> tree
  (** Input a tagged biniou value of type {!tree}. *)

val tree_of_string :
  ?pos:int -> string -> tree
  (** Deserialize a biniou value of type {!tree}.
      @param pos specifies the position where 
                 reading starts. Default: 0. *)

val create_tree :
  members: person list ->
  filiations: filiation list ->
  unit -> tree
  (** Create a record of type {!tree}. *)


5  Library

A library named atdgen is installed by the standard installation process. Only a fraction of it is officially supported and documented. The documentation is available online at http://oss.wink.com/atdgen/atdgen-1.0.0/odoc/index.html.
This document was translated from LATEX by HEVEA.