passing unit to uncurried function

[jey]

I seem to be hitting an edge case when trying to pass unit to an uncurried function. My intention is to create a Js.Promise.t(unit) representing the completion of a side-effect.

let x: Js.Promise.t(unit) =
  Js.Promise.make((~resolve, ~reject) => {
    /* causes compile error:
     *
     *    Found uncurried application [@bs] with arity 1, where arity 0 was expected.
     *    This has type: `(. unit) => unit`, but somewhere wanted `(. unit) => 'a`
     *
     * and gets turned into `resolve(.)` by refmt
     */
    //resolve(. ());

    /* works as expected
     */
    let nil = ();
    resolve(. nil);

    /* mysteriously works. maybe because "zero-arity" functions don't exist,
     * they are actually unary functions taking unit, so `ignore` has inferred
     * type `unit => unit`
     */
    resolve(. ignore());

    /* but then why not this? perhaps because the above only applies when currying.
     */
    //resolve(.);
  });

[bobzhang]

since in ocaml, there is no function which has arity zero, so that fn (.) is taken as a special form that fn is supposed to have zero arity.
In this case, reason could be improved to differentiate between resolve(. ()) and resolve(.), I will ask

[bobzhang]

@jey I created such issue in reason repo, you can comment it there.

[ryyppy]

The latest solution to this problem is implemented in a draft PR within the rescript syntax repo.

The code needs to expand into some more code, so it's not clear yet if this is the best solution.