This uses babel to parse javascript, and then translates that AST into the Ocaml AST, outputting JSON that refmt can accept.

To use:

$ ./run.sh 'alert("hello world")'
alert "hello world";

The goal of rejs is to help automate the process of porting JavaScript libraries into Reason. Eventually, if complete enough, rejs would generate a Reason project that is "correct", but that does not type check. The user would then need to fix all of the type errors, and do some basic refactoring in order to complete the port. rejs should cut out the most boring part of porting libraries - manually transcribing code from one language/syntax to another.

rejs is very new, and incomplete, but a few approaches should be explored.

• Transpiling JavaScript records to ML records (which requires a bunch of manual work to get it to type check).
• Transpiling JavaScript records to ML objects (which requires less manual work, but limits performance of resulting library).
• Embed placeholder strings of JS text where the port is not yet complete, which developers must manually port.

• Sometimes, a library will only be maintained in JavaScript for the foreseeable future, and you may not want to keep up your Reason fork with ongoing changes upstream. rejs's goal is to be a tool for JavaScript library maintainers, or people looking to fork JavaScript libraries to performance oriented ports.
• You may not be interested in porting your JavaScript library to Reason if your library doesn't have strict performance requirements, or if you do not see the value in sound+static type checking.

You may want to port a library into Reason if:

• You want to benefit from sound, static typing.
• You want your library to run in as many environments as possible, with the best performance possible for each environment. A library written in Reason has strictly more options for deployment and performance outcomes. For example, you may compile your Reason library as a native binary, running without a VM for maximum performance, but you may also compile that same library to JavaScript - you don't have to choose up front.

You need Reason with this PR applied, built in a directory adjacent to where you have this repo. You'll clone Reason and checkout the JsonSupport branch which has that PR applied. e.g.

Make sure you've pinned all the required packages mentioned in the Contributing To Development section of the Reason README

git clone https://github.com/facebook/Reason
(cd Reason; git checkout JsonSupport; make)
git clone https://github.com/jaredly/rejs
cd rejs

Lots of AST forms haven't been processed yet.

Look in js-item-to-re.js, and you can use https://github.com/babel/babylon/blob/master/ast/spec.md as a guide.

To find out what the desired Reason AST looks like, you can do

echo 'alert "hi"'|../Reason/refmt_impl.native  -parse re -print json -use-stdin true -is-interface-pp false

To find out what JS ast looks like:

./jsdump.js 'alert("hi")'

Translating

function() {
  if (x) {
    a()
    return b
  }
  c()
  return d
}

into

function() {
  if (x) {
    a()
    b
  } else {
    c()
    d
  }
}

Another option is to just add a [@return] annotation, to remind you to go through and make the return actually return. B/c some things would be pretty difficult (returning in the middle of a for loop, for example)