package bap-std

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package bap-std
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Universal Values.

This module creates an extensible variant type, that resembles extensible variant types, introduced in 4.02, but even more safe and more extensible, and, what really matters, serializable. Basically you should think of Value.t as a union type, aka sum type, that can be extended in any place, including your plugin code. Where extending is adding new constructor. To add new constructor, you need to register it, e.g.,

let function_signature = Value.Tag.register (module String)
    ~name:"function_signature"
    ~uuid:"2175c28c-08ca-4052-8385-3a01e1c6ab6f"

This is merely equivalent to adding a branch

| Function_signature of string

to existing union type. The main difference is that the name shouldn't be unique (in fact name doesn't bear any semantic meaning, it basically for pretty-printing). On the other hand the uuid parameter must be unique across the universe, space and time. To get the UUID with such properties, you can use uuidgen program that is usually available on Linux and Mac OS.

name and uuid must be strings, known at compile time, in other words it must be string literal, not just an arbitrary string, created dynamically. This is made intentionally, in order to prevent the abuse of the system.

The (module String) syntax creates a value from the module String, (so called first-class module). The module should implement Value.S signature, that requires pretty-printing, comparison function and serialization.

module type S = sig
  type t with bin_io, compare, sexp

  val pp : Format.formatter -> t -> unit
end

The good news is that, most of the types in Core and Bap do conform with the requirements. Usually, one can implement the requirements very easily by using type-driven syntax extensions (although, you still need to implement pretty-printing function yourself):

module Loc = struct
  type t = string * int * int
  with bin_io, compare, sexp

  let pp ppf (file,line,col) =
    Format.fprintf ppf "%s:%d:%d" file line col
end

let loc = Value.Tag.register (module Loc)
    ~name:"loc"
    ~uuid:"400e190e-ce21-488d-87b1-c101709621a8"

The returned value, is a tag that can be used to constructed values of that branch, and to deconstruct (extract) them. You may think of it as a cipher key, that is used to package data into the value container, and later to unpack it:

# let main_pos = Value.create loc ("test.c", 20, 2);;
val main_pos : value = test.c:20:2

You may see, that OCaml pretty-prints the value. That's neat! Also, you may see, that the returned expression has type value. That means that it can be used uniformly with other values, for example, you can put them in one container, e.g.,

# let main_t = Value.create function_signature
      "void main(int argc, const char *argv[])";;
val main_t : value = void main(int argc, const char *argv[])
# let main = [main_pos; main_t];;
val main : value list = [
    test.c:20:2;
    void main(int argc, const char *argv[])
  ]

To extract value you can use Value.get function:

# Value.get loc main_pos;;
- : Loc.t option = Some ("test.c", 20, 2)

This will require an extra allocation of an option container, and in a performance critical context it may be unacceptable. For this special case you can use a more efficient:

if Value.is loc then Value.get_exn loc main_pos

.

Underneath the hood, the values of type value is just a pair of an original value and runtime type information.

The comparison of two values of type value is actually a multi-method, as it has the following behavior:

1. If both values has the same type, then use compare function, that was provided for this type. 2. If values are of different types, that are known to the type system, then compare them using RTTI, and ignore the value. 3. If at least one of the values is of the unknown type, (i.e., type wasn't registered in the type system), then use polymorphic compare on a tuple of UUID and binary representation of the values.

The rules above guarantee, that values with different RTTI id are never equal. It also guarantees that the ordering will be preserved between different builds of a program, and even between different versions of the compiler.

Thread safety

The only thread unsafe function is register, that should be called in the module initialization time. In general programs modules are initialized in a single thread, so this shouldn't be an issue. The implementation by itself doesn't call register.

type t = value

a universal value

include Core_kernel.Bin_prot.Binable.S with type t := t
include Ppx_sexp_conv_lib.Sexpable.S with type t := t
type 'a tag

Tag constructor of type 'a

module type S = sig ... end

A required interface for the type to be lifted to value.

type void

uninhabited type

type literal = (void, void, void) Core_kernel.format

literal string. Don't look at the right hand side of a type equation, this is just a way to say that a string should be a literal not a value. Compiler will automatically coerce your string literals to this type.

type typeid

persistent type identifier

val bin_shape_typeid : Core_kernel.Bin_prot.Shape.t
val bin_size_typeid : typeid Core_kernel.Bin_prot.Size.sizer
val bin_write_typeid : typeid Core_kernel.Bin_prot.Write.writer
val bin_writer_typeid : typeid Core_kernel.Bin_prot.Type_class.writer
val bin_read_typeid : typeid Core_kernel.Bin_prot.Read.reader
val __bin_read_typeid__ : (int -> typeid) Core_kernel.Bin_prot.Read.reader
val bin_reader_typeid : typeid Core_kernel.Bin_prot.Type_class.reader
val bin_typeid : typeid Core_kernel.Bin_prot.Type_class.t
val compare_typeid : typeid -> typeid -> int
val sexp_of_typeid : typeid -> Ppx_sexp_conv_lib.Sexp.t
val typeid_of_sexp : Ppx_sexp_conv_lib.Sexp.t -> typeid
val create : 'a tag -> 'a -> t

create cons x creates a value using constructor cons and argument x

val is : 'a tag -> t -> bool

is cons v true if value v was constructed with constructor cons, i.e., it is true only when is_cons t (create t x)

val get : 'a tag -> t -> 'a option

get cons extracts a value associated with a constructor cons (Essentially, performs a pattern match on the specified variant branch)

val get_exn : 'a tag -> t -> 'a

get_exn t v extracts value created with t from the variant. Raises unspecified exception if variant v wasn't created with t.

val tagname : t -> string

tagname value returns a constructor name of the value

val typeid : t -> typeid

typeid value returns a type identifier of the value

module Tag : sig ... end

Variants of values.

module Match : sig ... end

Runtime parallel match.

Persistent type identifiers.

Although values of type value implements regular interface it is recommended to used dict data structure instead of those, that are provided by Regular interface.x

include Regular.Std.Regular.S with type t := t
include Core_kernel.Bin_prot.Binable.S with type t := t
val bin_size_t : t Bin_prot.Size.sizer
val bin_write_t : t Bin_prot.Write.writer
val bin_read_t : t Bin_prot.Read.reader
val __bin_read_t__ : (int -> t) Bin_prot.Read.reader
val bin_shape_t : Bin_prot.Shape.t
val bin_writer_t : t Bin_prot.Type_class.writer
val bin_reader_t : t Bin_prot.Type_class.reader
val bin_t : t Bin_prot.Type_class.t
include Ppx_sexp_conv_lib.Sexpable.S with type t := t
val t_of_sexp : Sexplib0__.Sexp.t -> t
val sexp_of_t : t -> Sexplib0__.Sexp.t
include Regular.Std.Printable.S with type t := t
val to_string : t -> string

to_string x returns a human-readable representation of x

val str : unit -> t -> string

str () t is formatted output function that matches "%a" conversion format specifier in functions, that prints to string, e.g., sprintf, failwithf, errorf and, surprisingly all Lwt printing function, including Lwt_io.printf and logging (or any other function with type ('a,unit,string,...) formatN`. Example:

Or_error.errorf "type %a is not valid for %a"
  Type.str ty Exp.str exp
val pps : unit -> t -> string

synonym for str

val ppo : Core_kernel.Out_channel.t -> t -> unit

will print to a standard output_channel, useful for using in printf, fprintf, etc.

val pp_seq : Stdlib.Format.formatter -> t Core_kernel.Sequence.t -> unit

prints a sequence of values of type t

this will include pp function from Core that has type t printer, and can be used in Format.printf family of functions

include Core_kernel.Pretty_printer.S with type t := t
val pp : Base__.Formatter.t -> t -> unit
include Core_kernel.Comparable.S_binable with type t := t
include Base.Comparable.S with type t := t
val (>=) : t -> t -> bool
val (<=) : t -> t -> bool
val (=) : t -> t -> bool
val (>) : t -> t -> bool
val (<) : t -> t -> bool
val (<>) : t -> t -> bool
val equal : t -> t -> bool
val compare : t -> t -> int
val min : t -> t -> t
val max : t -> t -> t
val ascending : t -> t -> int
val descending : t -> t -> int
val between : t -> low:t -> high:t -> bool
val clamp_exn : t -> min:t -> max:t -> t
val clamp : t -> min:t -> max:t -> t Base__.Or_error.t
type comparator_witness
val validate_lbound : min:t Base__.Maybe_bound.t -> t Base__.Validate.check
val validate_ubound : max:t Base__.Maybe_bound.t -> t Base__.Validate.check
val validate_bound : min:t Base__.Maybe_bound.t -> max:t Base__.Maybe_bound.t -> t Base__.Validate.check
module Replace_polymorphic_compare : sig ... end
include Core_kernel.Comparator.S with type t := t with type comparator_witness := comparator_witness
include Core_kernel.Hashable.S_binable with type t := t
val hash_fold_t : Ppx_hash_lib.Std.Hash.state -> t -> Ppx_hash_lib.Std.Hash.state
val hash : t -> Ppx_hash_lib.Std.Hash.hash_value
val hashable : t Core_kernel__.Hashtbl.Hashable.t
include Regular.Std.Data.S with type t := t
type info = string * [ `Ver of string ] * string option

name,Ver v,desc information attached to a particular reader or writer.

val version : string

Data representation version. After any change in data representation the version should be increased.

Serializers that are derived from a data representation must have the same version as a version of the data structure, from which it is derived. This kind of serializers can only read and write data of the same version.

Other serializers can actually read and write data independent on its representation version. A serializer, that can't store data of current version simply shouldn't be added to a set of serializers.

It is assumed, that if a reader and a writer has the same name and version, then whatever was written by the writer should be readable by the reader. The round-trip equality is not required, thus it is acceptable if some information is lost.

It is also possible, that a reader and a writer that has the same name are compatible. In that case it is recommended to use semantic versioning.

val size_in_bytes : ?ver:string -> ?fmt:string -> t -> int

size_in_bytes ?ver ?fmt datum returns the amount of bytes that is needed to represent datum in the given format and version

val of_bytes : ?ver:string -> ?fmt:string -> Regular.Std.bytes -> t

of_bytes ?ver ?fmt bytes deserializes a value from bytes.

val to_bytes : ?ver:string -> ?fmt:string -> t -> Regular.Std.bytes

to_bytes ?ver ?fmt datum serializes a datum to a sequence of bytes.

val blit_to_bytes : ?ver:string -> ?fmt:string -> Regular.Std.bytes -> t -> int -> unit

blit_to_bytes ?ver ?fmt buffer datum offset copies a serialized representation of datum into a buffer, starting from the offset.

val of_bigstring : ?ver:string -> ?fmt:string -> Core_kernel.bigstring -> t

of_bigstring ?ver ?fmt buf deserializes a datum from bigstring

val to_bigstring : ?ver:string -> ?fmt:string -> t -> Core_kernel.bigstring

of_bigstring ?ver ?fmt datum serializes a datum to a sequence of bytes represented as bigstring

val blit_to_bigstring : ?ver:string -> ?fmt:string -> Core_kernel.bigstring -> t -> int -> unit

blit_to_bigstring ?ver ?fmt buffer datum offset copies a serialized representation of datum into a buffer, starting from offset.

module Io : sig ... end

Input/Output functions for the given datum.

module Cache : sig ... end

Data cache.

val add_reader : ?desc:string -> ver:string -> string -> t Regular.Std.reader -> unit

add_reader ?desc ~ver name reader registers a new reader with a provided name, version ver and optional description desc

val add_writer : ?desc:string -> ver:string -> string -> t Regular.Std.writer -> unit

add_writer ?desc ~ver name writer registers a new writer with a provided name, version ver and optional description desc

val available_readers : unit -> info list

available_reader () lists available readers for the data type

val default_reader : unit -> info

default_reader returns information about default reader

val set_default_reader : ?ver:string -> string -> unit

set_default_reader ?ver name sets new default reader. If version is not specified then the latest available version is used. Raises an exception if a reader with a given name doesn't exist.

val with_reader : ?ver:string -> string -> (unit -> 'a) -> 'a

with_reader ?ver name operation temporary sets a default reader to a reader with a specified name and version. The default reader is restored after operation is finished.

val available_writers : unit -> info list

available_writer () lists available writers for the data type

val default_writer : unit -> info

default_writer returns information about the default writer

val set_default_writer : ?ver:string -> string -> unit

set_default_writer ?ver name sets new default writer. If version is not specified then the latest available version is used. Raises an exception if a writer with a given name doesn't exist.

val with_writer : ?ver:string -> string -> (unit -> 'a) -> 'a

with_writer ?ver name operation temporary sets a default writer to a writer with a specified name and version. The default writer is restored after operation is finished.

val default_printer : unit -> info option

default_writer optionally returns an information about default printer

val set_default_printer : ?ver:string -> string -> unit

set_default_printer ?ver name sets new default printer. If version is not specified then the latest available version is used. Raises an exception if a printer with a given name doesn't exist.

val with_printer : ?ver:string -> string -> (unit -> 'a) -> 'a

with_printer ?ver name operation temporary sets a default printer to a printer with a specified name and version. The default printer is restored after operation is finished.

Low level access to serializers

val find_reader : ?ver:string -> string -> t Regular.Std.reader option

find_reader ?ver name lookups a reader with a given name. If version is not specified, then a reader with maximum version is returned.

val find_writer : ?ver:string -> string -> t Regular.Std.writer option

find_writer ?ver name lookups a writer with a given name. If version is not specified, then a writer with maximum version is returned.

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