Atdgen reference manual
release 1.3.1

Martin Jambon
© 2010–2011 MyLife

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 uses the following packages that were developed in conjunction with Atdgen:

atd: parser for the syntax of type definitions
biniou: parser and printer for biniou, a binary extensible data format
yojson: parser and printer for JSON, a widespread text-based data format

Atdgen does not use Camlp4.

2 Command-line usage

2.1 Command-line help

$ atdgen -help

Generate OCaml code offering:
  * OCaml type definitions translated from ATD file (-t)
  * serializers and deserializers for Biniou (-b)
  * serializers and deserializers for JSON (-j)
  * record-creating functions supporting default fields (-v)
  * user-specified data validators (-v)

Recommended usage: ./atdgen (-t|-b|-j|-v|-dep|-list) example.atd
  -t 
          Produce files example_t.mli and example_t.ml
          containing OCaml type definitions derived from example.atd.
  -b 
          Produce files example_b.mli and example_b.ml
          containing OCaml serializers and deserializers for the Biniou
          data format from the specifications in example.atd.
  -j 
          Produce files example_j.mli and example_j.ml
          containing OCaml serializers and deserializers for the JSON
          data format from the specifications in example.atd.
  -v 
          Produce files example_v.mli and example_v.ml
          containing OCaml functions for creating records and
          validators from the specifications in example.atd.
  -dep 
          Output Make-compatible dependencies for all possible
          products of atdgen -t, -b, -j and -v, and exit.
  -list 
          Output a space-separated list of all possible products of
          atdgen -t, -b, -j and -v, and exit.
  -o [ PREFIX | - ]
          Use this prefix for the generated files, e.g. 'foo/bar' for
          foo/bar.ml and foo/bar.mli.
          `-' designates stdout and produces code of the form
            struct ... end : sig ... end
  -biniou 
          [deprecated in favor of -t and -b]
          Produce serializers and deserializers for Biniou
          including OCaml type definitions (default).
  -json 
          [deprecated in favor of -t and -j]
          Produce serializers and deserializers for JSON
          including OCaml type definitions.
  -j-std 
          Convert tuples and variants into standard JSON and
          refuse to print NaN and infinities (implying -json mode
          unless another mode is specified).
  -std-json 
          [deprecated in favor of -j-std]
          Same as -j-std.
  -j-pp <func>
          OCaml function of type (string -> string) applied on the input
          of each *_of_string function generated by atdgen (JSON mode).
          This is originally intended for UTF-8 validation of the input
          which is not performed by atdgen.
  -j-defaults 
          Output JSON record fields even if their value is known
          to be the default.
  -j-strict-fields 
          Call !Ag_util.Json.unknown_field_handler for every unknown JSON field
          found in the input instead of simply skipping them.
          The initial behavior is to raise an exception.
  -j-custom-fields FUNCTION
          Call the given function of type (string -> unit)
          for every unknown JSON field found in the input
          instead of simply skipping them.
          See also -j-strict-fields.
  -validate 
          [deprecated in favor of -t and -v]
          Produce data validators from <ocaml validator="x"> annotations
          where x is a user-written validator to be applied on a specific
          node.
          This is typically used in conjunction with -extend because
          user-written validators depend on the type definitions.
  -extend MODULE
          Assume that all type definitions are provided by the specified
          module unless otherwise annotated. Type aliases are created
          for each type, e.g.
            type t = Module.t
  -open MODULE1,MODULE2,...
          List of modules to open (comma-separated or space-separated)
  -nfd 
          Do not dump OCaml function definitions
  -ntd 
          Do not dump OCaml type definitions
  -pos-fname FILENAME
          Source file name to use for error messages
          (default: input file name)
  -pos-lnum LINENUM
          Source line number of the first line of the input (default: 1)
  -rec 
          Keep OCaml type definitions mutually recursive
  -o-name-overlap 
          Accept records and classic (non-polymorphic) variants with identical
          field or constructor names in the same module. Overlapping names are
          supported in OCaml since version 4.01.

          Duplicate name checking will be skipped, and type annotations will
          be included in the implementation to disambiguate names.
          This is the default if atdgen was compiled for OCaml >= 4.01.0
  -o-no-name-overlap 
          Disallow records and classic (non-polymorphic) variants
          with identical field or constructor names in the same module.
          This is the default if atdgen was compiled for OCaml < 4.01.0
  -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 -t example.atd
$ atdgen -b 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;
}

is used to produce files example_t.mli, example_t.ml, example_b.mli and example_b.ml. This is example_b.mli:

(* Auto-generated from "example.atd" *)


type gender = Example_t.gender

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

type profile = Example_t.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 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 :
  ?len: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 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 :
  ?len: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. *)

(* 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 :
  ?len: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. *)

Module Example_t (files example_t.mli and example_t.ml) contains all OCaml type definitions that can be used independently from Biniou or JSON.

For convenience, these definitions are also made available from the Example_b module whose interface is shown above. Any type name, record field name or variant constructor can be referred to using either module. For example, the OCaml expressions ((x : Example_t.date) : Example_b.date) and x.Example_t.year = x.Example_b.year are both valid.

2.3 Atdgen-json example

$ atdgen -t example.atd
$ atdgen -j 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;
}

is used to produce files example_t.mli, example_t.ml, example_j.mli and example_j.ml. This is example_j.mli:

(* Auto-generated from "example.atd" *)


type gender = Example_t.gender

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

type profile = Example_t.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_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_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 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}. *)

Module Example_t (files example_t.mli and example_t.ml) contains all OCaml type definitions that can be used independently from Biniou or JSON.

For convenience, these definitions are also made available from the Example_j module whose interface is shown above. Any type name, record field name or variant constructor can be referred to using either module. For example, the OCaml expressions ((x : Example_t.date) : Example_j.date) and x.Example_t.year = x.Example_j.year are both valid.

2.4 Validator example

$ atdgen -t example.atd
$ atdgen -v example.atd

Input file example.atd:

type month = int <ocaml validator="fun x -> x >= 1 && x <= 12">
type day = int <ocaml validator="fun x -> x >= 1 && x <= 31">

type date = {
  year : int;
  month : month;
  day : day;
}
  <ocaml validator="Date_util.validate_date">

is used to produce files example_t.mli, example_t.ml, example_v.mli and example_v.ml. This is example_v.ml, showing how the user-specified validators are used:

(* Auto-generated from "example.atd" *)


type month = Example_t.month

type day = Example_t.day

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

let validate_month = (
  fun x -> x >= 1 && x <= 12
)
let validate_day = (
  fun x -> x >= 1 && x <= 31
)
let validate_date : _ -> date -> _ = (
  fun path x ->
    match ( Date_util.validate_date ) path x with
      | Some _ as err -> err
      | None ->
        match
          (
            validate_month
          ) (‘Field "month" :: path) x.month
        with
          | Some _ as err -> err
          | None ->
            (
              validate_day
            ) (‘Field "day" :: path) x.day
)
let create_date 
  ~year
  ~month
  ~day
  () : date =
  {
    year = year;
    month = month;
    day = day;
  }

3 Default type 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
shared	no wrapping	shared	not implemented
variants	polymorphic variants	regular variants	variants
record	record	record	object
tuple	tuple	tuple	tuple

Notes:

The JSON null value serves only as the unit value and is useful in practice only for instanciating parametrized types with “nothing”. Option types have a distinct representation that does not use the null value.
OCaml floats are written to JSON numbers with either a decimal point or an exponent such that they are distinguishable from ints, even though the JSON standard does not require a distinction between the two.
The optional values of record fields denoted in ATD by a question mark are unwrapped or omitted in both biniou and JSON.
JSON option values and JSON variants are represented in standard JSON (atdgen -j -j-std) by a single string e.g. "None" or a pair in which the first element is the name (constructor) e.g. ["Some", 1234]. Yojson also provides a specific syntax for variants using edgy brackets: <"None">, <"Some": 1234>.
Biniou field names and variant names other than the option types use the hash of the ATD field or variant name and cannot currently be overridden by annotations.
JSON tuples in standard JSON (atdgen -j -j-std) use the array notation e.g. ["ABC", 123]. Yojson also provides a specific syntax for tuples using parentheses, e.g. ("ABC", 123).
Types defined as abstract are defined in another module.

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;
}

Floating-point numbers

Position: after float type

Values: float64 (default), float32

Semantics: float32 allows for a shorter serialized representation of floats, using 4 bytes instead of 8, with reduced precision. OCaml floats always use 8 bytes, though.

Example:

type t = {
  lat : float <biniou repr="float32">;
  lon : float <biniou repr="float32">;
}

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"
}

4.2.2 Field json.repr

Association lists

Position: after (string * _) list type

Values: object

Semantics: uses JSON’s object notation to represent association lists.

Example:

type counts = (string * int) list <json repr="object">

A valid JSON object of the counts type above is:

{
  "bob": 3,
  "john": 1408,
  "mary": 450987,
  "peter": 93087
}

Without the annotation <json repr="object">, the data above would be represented as:

[
  [ "bob", 3 ],
  [ "john", 1408 ],
  [ "mary", 450987 ],
  [ "peter", 93087 ]
]

Floats

Position: after float type

Values: int

Semantics: specifies a float value that must be rounded to the nearest integer and represented in JSON without a decimal point nor an exponent.

Example:

type unixtime = float <json repr="int">

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.from

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

Values: OCaml module name without the _t, _b, _j or _v suffix. This can be also seen as the name of the original ATD file, without the .atd extension and capitalized like an OCaml module name.

Semantics: specifies the base name of the OCaml modules where the type and values coming with that type are defined.

It is useful for ATD types defined as abstract and for types annotated as predefined using the annotation <ocaml predef>. In both cases, the missing definitions must be provided by modules composed of the base name and the standard suffix assumed by Atdgen which is _t, _b, _j or _v.

Example: First input file part1.atd:

type point = { x : int; y : int }

Second input file part2.atd depending on the first one:

type point <ocaml from="Part1"> = abstract
type points = point list

4.3.5 Field ocaml.module

In most cases since Atdgen 1.2.0 module annotations are deprecated in favor of from annotations previously described.

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

Values: OCaml module name

Semantics: specifies the OCaml module where the type and values coming with that type are defined. It is useful for ATD types defined as abstract and for types annotated as predefined using the annotation <ocaml predef>. In both cases, the missing definitions can be provided either by globally opening an OCaml module with an OCaml directive or by specifying locally the name of the module to use.

The latter approach is recommended because it allows to create type and value aliases in the OCaml module being generated. It results in a complete module signature regardless of the external nature of some items.

Example: Input file example.atd:

type document <ocaml module="Doc"> = abstract

type color <ocaml predef module="Color"> =
  [ Black | White ] <ocaml repr="classic">

type point <ocaml predef module="Point"> = {
  x : float;
  y : float;
}

gives the following OCaml type definitions (file example.mli):

type document = Doc.document

type color = Color.color =  Black | White

type point = Point.point = { x: float; y: float }

Now for instance Example.Black and Color.Black can be used interchangeably in other modules.

4.3.6 Field ocaml.t

Position: left-hand side of a type definition, after the type name. Must be used in conjunction with a module field.

Values: OCaml type name as found in an external module.

Semantics: This option allows to specify the name of an OCaml type defined in an external module.

It is useful when the type needs to be renamed because its original name is already in use or not enough informative. Typically we may want to give the name foo to a type originally defined in OCaml as Foo.t.

Example:

type foo <ocaml_biniou module="Foo" t="t"> = abstract
type bar <ocaml_biniou module="Bar" t="t"> = abstract
type t <ocaml_biniou module="Baz"> = abstract

allows local type names to be unique and gives the following OCaml type definitions:

type foo = Foo.t
type bar = Bar.t
type t = Baz.t

4.3.7 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;
}

4.3.8 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;
}

4.3.9 Field ocaml.repr

Integers

Position: after int type

Values: char, int32, int64, float

Semantics: specifies an alternate type for representing integers. The default type is int, but char, int32, int64 or float can be used instead.

The three types char, int32 and int64 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.

The type float is only supported in conjunction with JSON and is useful when an OCaml float is used to represent an integral value, such as a time in seconds returned by Unix.time(). When converted into JSON, floats are rounded to the nearest integer.

Example:

type t = {
  id : int
    <ocaml repr="int64">
    <biniou repr="int64">;
  data : string list;
}

Lists and arrays

Position: after a 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

Shared values

Position: after a shared type

Values: ref

Semantics: wraps the value using OCaml’s ref type, which is as of Atdgen 1.1.0 the only way of sharing values other than records.

Example:

type shared_string = string shared <ocaml repr="ref">

translates to the following OCaml type definition:

type shared_string = string ref

4.3.10 Field ocaml.validator

Position: after any type expression except type variables

Values: OCaml function that takes one argument of the given type and returns a bool

Semantics: atdgen -v produces for each type named t a function validate_t:

val validate_t : t -> bool

Such a function returns true if and only if the value and all of its subnodes pass all the validators specified by annotations of the form <ocaml validator="...">.

Example:

type positive = int <ocaml validator="fun x -> x > 0">

type point = {
  x : positive;
  y : positive;
  z : int;
}
  <ocaml validator="Point.validate">
  (* Some validating function from a user-defined module Point *)

The generated validate_point function is equivalent to the following:

let validate_point p =
  Point.validate p
  && (fun x -> x > 0) p.x
  && (fun x -> x > 0) p.y

4.4 Section ocaml_biniou

Section ocaml_biniou takes precedence over section ocaml in Biniou mode (-b) for the following fields:

predef (see 4.3.1)
module (see 4.3.5)
t (see 4.3.6)

4.5 Section ocaml_json

Section ocaml_json takes precedence over section ocaml in JSON mode (-j) for the following fields:

predef (see 4.3.1)
module (see 4.3.5)
t (see 4.3.6)

Example:

This example shows how to parse a field into a generic tree of type Yojson.Safe.json rather than a value of a specialized OCaml type.

type dyn <ocaml_json module="Yojson.Safe" t="json"> = abstract

type t = { foo: int; bar: dyn }

translates to the following OCaml type definitions:

type dyn = Yojson.Safe.json

type t = { foo : int; bar : dyn }

Sample OCaml value of type t:

{
  foo = 12345;
  bar =
    ‘List [
      ‘Int 12;
      ‘String "abc";
      ‘Assoc [
        "x", ‘Float 3.14;
        "y", ‘Float 0.0;
        "color", ‘List [ ‘Float 0.3; ‘Float 0.0; ‘Float 1.0 ]
      ]
    ]
}

Corresponding JSON data as obtained with string_of_t:

{"foo":12345,"bar":[12,"abc",{"x":3.14,"y":0.0,"color":[0.3,0.0,1.0]}]}

4.6 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.

4.6.1 Field doc.text

Position:

after the type name on the left-hand side of a type definition
after the type expression on the right hand of a type definition (but not after any type expression)
after record field names
after variant names

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

Semantics: The markup language is defined as follows:

Blank lines separate paragraphs.
{{ }} can be used to enclose inline verbatim text.
{{{ }}} can be used to enclose verbatim text where whitespace is preserved.
The backslash character is used to escape special character sequences. In regular paragraph mode the special sequences are [\], [] and []. In inline verbatim text, special sequences are [\] and []. In verbatim text, special sequences are [\] and [].

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 -b 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 -b genealogy.atd into the following OCaml interface file genealogy_b.mli with ocamldoc-compliant comments:

(* Auto-generated from "genealogy.atd" *)


(** Type definitions for family trees *)

(**
  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 = Genealogy_t.person_id

(** Gender, definition depending on the context *)
type gender = Genealogy_t.gender

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

(**
  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 = Genealogy_t.filiation_type = {
  genetic: bool option;
  pregnancy: bool option;
  raised_from_birth: bool option;
  raised: bool option;
  stepchild: bool option;
  adopted: bool option
}

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

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

(* 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 :
  ?len: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 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 :
  ?len: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 :
  ?len: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. *)

(* 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 :
  ?len: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. *)

(* 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 :
  ?len: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. *)

(* 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 :
  ?len: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. *)

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-1.3.1/odoc/index.html.

This document was translated from L^AT_EX by H^EV^EA.

Atdgen reference manual release 1.3.1

Martin Jambon © 2010–2011 MyLife

Contents

1 Introduction

2 Command-line usage

2.1 Command-line help

2.2 Atdgen-biniou example

2.3 Atdgen-json example

2.4 Validator example

3 Default type mapping

4 ATD Annotations

4.1 Section biniou

4.1.1 Field biniou.repr

Integers

Floating-point numbers

Arrays and tables

4.2 Section json

4.2.1 Field json.name

4.2.2 Field json.repr

Association lists

Floats

4.3 Section ocaml

4.3.1 Field ocaml.predef

4.3.2 Field ocaml.mutable

4.3.3 Field ocaml.default

4.3.4 Field ocaml.from

4.3.5 Field ocaml.module

4.3.6 Field ocaml.t

4.3.7 Field ocaml.field_prefix

4.3.8 Field ocaml.name

4.3.9 Field ocaml.repr

Integers

Lists and arrays

Sum types

Shared values

4.3.10 Field ocaml.validator

4.4 Section ocaml_biniou

4.5 Section ocaml_json

4.6 Section doc

4.6.1 Field doc.text

5 Library

Atdgen reference manual
release 1.3.1

Martin Jambon
© 2010–2011 MyLife