Atdgen reference manual
                        ***********************
                             release 1.2.2
                             *************
                             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 
     
      - 4.2  Section json 
        
         - 4.2.1  Field json.name 
         - 4.2.2  Field json.repr 
     
      - 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 
         - 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 
   
  

1  Introduction
*=*=*=*=*=*=*=*

  
  Atdgen is a command-line program that takes as input type definitions
in the ATD (1) syntax and produces OCaml code suitable for data
serialization and deserialization.
  Two data formats are currently supported, these are biniou (2)  and
JSON (3). 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 (4): 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-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
    -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 date = Example_t.date = { year: int; month: int; day: int }
  
  type gender = Example_t.gender
  
  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 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 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 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 date = Example_t.date = { year: int; month: int; day: int }
  
  type gender = Example_t.gender
  
  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_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_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}. *)
  
>>
  
  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 = (
    fun x ->
      ( Date_util.validate_date ) x &&
      (
        validate_month
      ) x.month
      &&
      (
        validate_day
      ) x.day
  )
  let create_date 
    ~year
    ~month
    ~day
    () =
    {
      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;
  }
>>
  
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
----------------------
  
  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 ]
  ]
>>
  
  

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
  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 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 *)
  
  (**
    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
  }
  
  (**
    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
  
  (** Connection between parent or primary caretaker and child *)
  type filiation = Genealogy_t.filiation = {
    parent: person_id;
    child: person_id;
    filiation_type: filiation_type
  }
  
  (** 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 *)
  }
  
  type tree = Genealogy_t.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 :
    ?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 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 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 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 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-1.2.2/odoc/index.html.  
-----------------------------------------------------------------------
  
   This document was translated from LaTeX by HeVeA (5).
-----------------------------------
  
  
 (1) http://oss.wink.com/atd/
 
 (2) http://martin.jambon.free.fr/biniou.html
 
 (3) http://json.org/
 
 (4) http://martin.jambon.free.fr/yojson.html
 
 (5) http://hevea.inria.fr/index.html