js_of_ocaml-ppx

Compiler from OCaml bytecode to JavaScript
README

Js_of_ocaml is a compiler from OCaml bytecode to JavaScript. It makes it
possible to run pure OCaml programs in JavaScript environment like browsers and
Node.js.

  • It is easy to install and use as it works with an existing installation of
    OCaml, with no need to recompile any library.

  • It comes with bindings for a large part of the browser APIs.

  • According to our benchmarks, the generated programs runs typically faster than
    with the OCaml bytecode interpreter.

  • We believe this compiler will prove much easier to maintain than a retargeted
    OCaml compiler, as the bytecode provides a very stable API.

Js_of_ocaml is composed of multiple packages:

  • js_of_ocaml-compiler, the compiler.

  • js_of_ocaml-ppx, a ppx syntax extension.

  • js_of_ocaml, the base library.

  • js_of_ocaml-ppx_deriving_json

  • js_of_ocaml-lwt, lwt support.

  • js_of_ocaml-tyxml, tyxml support.

  • js_of_ocaml-toplevel, lib and tools to build an ocaml toplevel to
    javascript.

Requirements

See
opam
file for version constraints.

optional

Toplevel requirements

  • tyxml, reactiveData

  • ocp-indent: needed to support indentation in the toplevel

  • higlo: needed to support Syntax highlighting in the toplevel

  • cohttp: needed to build the toplevel webserver

Installation

Opam

opam install js_of_ocaml js_of_ocaml-compiler js_of_ocaml-ppx

Usage

Your program must first be compiled using the OCaml bytecode compiler ocamlc.
JavaScript bindings are provided by the js_of_ocaml package. The syntax
extension is provided by js_of_ocaml-ppx package.

ocamlfind ocamlc -package js_of_ocaml -package js_of_ocaml-ppx -linkpkg -o cubes.byte cubes.ml

Then, run the js_of_ocaml compiler to produce JavaScript code:

js_of_ocaml cubes.byte

Features

Most of the OCaml standard library is supported. However,

  • Weak semantic cannot be implemented using JavaScript. A dummy implementation
    is provided.

  • Most of the Sys module is not supported.

Extra libraries distributed with OCaml (such as Thread) are not supported in
general. However,

  • Bigarray: bigarrays are supported using Typed Arrays

  • Num: supported

  • Str: supported

  • Graphics: partially supported using canvas (see js_of_ocaml-lwt.graphics)

  • Unix: time related functions are supported

Tail call is not optimized in general. However, mutually recursive functions are
optimized:

  • self recursive functions (when the tail calls are the function itself) are
    compiled using a loop.

  • trampolines are used otherwise.
    More about tail call
    optimization.

Data representation

Data representation differs from the usual one. Most notably, integers are 32
bits (rather than 31 bits or 63 bits), which is their natural size in
JavaScript, and floats are not boxed. As a consequence, marshalling, polymorphic
comparison, and hashing functions can yield results different from usual:

  • marshalling of floats is not supported (unmarshalling works);

  • the polymorphic hash function will not give the same results on datastructures
    containing floats;

  • these functions may be more prone to stack overflow.

| Ocaml | javascript |
| ------------- | ------------- |
| int | number (32bit int) |
| int32 | number (32bit int) |
| nativeint | number (32bit int) |
| int64 | Object (MlInt64) |
| float | number |
| string | string or object (MlBytes) |
| bytes | object (MlBytes) |
| "immediate" (e.g. true, false, None, ()) | number (32bit int) |
| "block" | array with tag as first element (e.g. C(1,2) => [tag,1,2]) |
| array | block with tag 0 (e.g. [\|1;2\|] => [0,1,2]) |
| tuple | block with tag 0 (e.g. (1,2) => [0,1,2]) |
| record | block (e.g. {x=1;y=2} => [0,1,2]) |
| contructor with arguments | block (e.g. C (1, 2) => [tag,1,2]) |
| module | block |
| exception and extensible variant | block or immediate |
| function | function |

Toplevel

Contents of the distribution

| Filename | Description |
| ----------- | -------------------------------------------- |
| LICENSE | license and copyright notice |
| README | this file |
| compiler/ | compiler |
| examples/ | small examples |
| lib/ | library for interfacing with JavaScript APIs |
| ppx/ | ppx syntax extensions |
| runtime/ | runtime system |
| toplevel/ | web-based OCaml toplevel |

Install
Sources
js_of_ocaml-4.0.0.tbz
sha256=df02f819e5b2f48234af2b3e3e7c9781afa8212f8bece7ebcfbd8358b394495e
sha512=92e822849c8be14ce0428f7f4be3991449f76e65d408073a5b8b9674ba2d099439027aa11618b603c7ee31a179cf6976d54a929917a69b269425f0367926c200
Dependencies
odoc
with-doc
re
>= "1.9.0" & with-test
ppx_expect
>= "v0.14.2" & with-test
num
with-test
ppxlib
>= "0.15.0"
js_of_ocaml
= version
ocaml
>= "4.04"
dune
>= "2.9"
Reverse Dependencies