Strange behavior when using unit in externals

[jchavarri]

The following code:

external useFoo : unit -> string -> string = "useFoo"

let foo = useFoo ()
let t = foo ""

generates this output:

function foo(param) {
  return useFoo(param);
}

var t = useFoo("");

Playground.

Note how t is converted into useFoo("") and not useFoo(undefined, ""). When using any other type, the first parameter will be passed just fine:

external useFoo : int -> string -> string = "useFoo"

let foo = useFoo 2
let t = foo ""

Output:

function foo(param) {
  return useFoo(2, param);
}

var t = useFoo(2, "");

Playground

Is this expected?

[anmonteiro]

I'm looking into this, but one workaround is:

type t = unit

external useFoo : t -> string -> string = "useFoo"

[anmonteiro]

I still need to do more digging, but the issue here seems to be that unit is ignored for cases like:

type t

external foo: unit -> t = ""

and generating foo() instead of foo(undefined)

[anmonteiro]

One idea is to only elide the unit argument when it appears before the return value, but a "return value" could be a function, too.

This might work well with uncurried.