Compile a polymorphic variant to a desired string cleanly

[jbhoot]

In order to compile a polymorphic variant to a desired string value in JavaScript, the following approach is required:

type x =
  [ `Document_fonts [@bs.as "document-fonts"]
  | `Browser_fonts [@bs.as "browser-fonts"]
  ]
[@@bs.deriving jsConverter]

let a : x = `Document_fonts
let b = xToJs `Document_fonts

The assignments are compiled to

var a = "Document_fonts";
var b = xToJs("Document_fonts");

out of which, b is correctly assigned the value "document-fonts".

However, [@@bs.deriving jsConverter] generates converter functions, which are also compiled and added to the JavaScript code. So the full compiled code is quite a bit:

var _map = {"Document_fonts":"document-fonts","Browser_fonts":"browser-fonts"};

var _revMap = {"document-fonts":"Document_fonts","browser-fonts":"Browser_fonts"};

function xToJs(param) {
  return _map[param];
}

function xFromJs(param) {
  return _revMap[param];
}

var b = xToJs("Document_fonts");

var a = "Document_fonts";

export {
  xToJs ,
  xFromJs ,
  a ,
  b ,
}

Things could be a lot cleaner:

1. The requirement of [@@bs.deriving jsConverter] attribute could be dropped, i.e., the definition of the polymorphic variant type, coupled with the [@bs.as "x"] attribute(s) should provide the intent adequately.
2. Ideally, i.e., from my understanding, the converter functions should not be needed and could be dropped too.
3. An assignment like

let a : x = `Document_fonts

for the above definition would ideally compile directly to

var a = "document-fonts";

[anmonteiro]

This isn't actually possible because we'd need to support defining polymorphic variants that break the OCaml syntax. i.e. it's not possible to write type x = [`foo-bar]