Js_of_ocaml bis

Why bis? & Purpose

Because, there is already a tool named `js_of_ocaml` whose job is to produce efficient Javascript from OCaml bytecode.

Here, we try to translate OCaml syntax to ECMAScript5 syntax, the purpose of it is to generate readable ECMAScript code, so that it could later be use in a step-by-step ECMAScript interpreter.

Dependencies

• `node.js` and the `esprima` package. In order to get the esprima package the more convenient way is to get `npm` (node package manager) and run `npm install esprima`.
• ocaml 4.02.1

How to run it

make
make tests
./run.sh tests/js/the_file_you_want_to_run.js

I you run into any error about *.cmi files that should not be present run the following command:

make cleanall

How does it work?

In order to get the statically typed abstract syntax tree (STAST) of OCaml we usethe same files that are used in the compiler of OCaml 4.02.1 (hence the dependency).

On top, of this STAST, there is a custom back-end that transliterate OCaml to ECMAScript. The code written in OCaml cannot rely on code from the typical standard library. Therefore a file named `stdlib.mli` (found in the directory `stdlib_ml`) contains all the required definitions for the exemples to work. This file as a twin which is `stdlib.js` found in `stdlib_js`, in this file the functions whose prototype is in `stdlib.mli` are defined here.

About the subset of OCaml supported

• Let (rec) declarations, except `let () = ` and `let _ =`.
• If then else statements, as excepted `if then else` statements return a value.
• Pattern matching, only one level of pattern matching over arbitrary types.
• Types declarations, if a constructor take arguments (one or more), you should add an annotations to provide default names for the parameters. See example below.

type 'a tree =
  | Leaf [@f value] of `a
  | Node [@f left, value, right] of `a tree * `a * `a tree          

Special note: from OCaml 4.02.2 annotations do not have the same syntax, but for now we work with OCaml 4.02.1 so the code above works and is recommended.