mel.uncurry only works with "first level callbacks"

[jchavarri]

Consider the following snippet (playground):

external map : (('a -> 'b -> 'c)[@mel.uncurry]) -> 'c array = "map"

let add x =
  let partial y = x + y in
  partial

let _ = map add

It generates the following code, with the add callback uncurried and inlined as expected:

function add(x) {
  return function (y) {
    return x + y | 0;
  };
}

map(function (param, param$1) {
      return param + param$1 | 0;
    });

Now, if we have a slightly different function (playground):

external map : ((('a -> 'b -> 'c)[@mel.uncurry]) -> unit) -> 'c array = "map"

let add f =
  f 1 2;
  ()

let _ = map add

It produces the following code:

function add(f) {
  Curry._2(f, 1, 2);
}

map(add);

I wonder if this is a fundamental limitation, or something that could be fixed? Worst case, we can document this behavior. cc @davesnx

[jchavarri]

@anmonteiro do you have any clue what could be going on? These alerts appear constantly while working on reason-react and it's both quite annoying and also scary that the uncurrying is not working properly for the callbacks.

Added a test in #875 to showcase the problem hopefully better.

[anmonteiro]

explanation why this doesn't work: https://github.com/melange-re/melange/pull/952/files#r1414511000