I found a subtle bug in production which is caused by comparing a sum type.

```
open Jest;
open ExpectJs;
type key =
| KeyPID(int)
| KeyVPID(int);
module KeyCmp =
Belt.Id.MakeComparable({
type t = key;
let cmp: (key, key) => int =
(a, b) =>
switch (a, b) {
| (KeyPID(x), KeyPID(y)) => compare(x, y)
| (KeyVPID(x), KeyVPID(y)) => compare(x, y)
| _ => 1
};
});
describe("OnpingStdLib_Compare", () => {
test("test comparable module functor working with set", () => {
let setA =
Belt.Set.fromArray(
[|
KeyPID(123),
KeyPID(456),
KeyVPID(789),
KeyVPID(910),
KeyPID(555),
|],
~id=(module KeyCmp),
);
let setB = Belt.Set.fromArray([|KeyVPID(789)|], ~id=(module KeyCmp));
let intersection = Belt.Set.intersect(setA, setB);
Js.log2("intersection", Belt.Set.toArray(intersection));
intersection |> Belt.Set.isEmpty |> expect |> toBe(false);
})
});
```

The `intersection`

results in an empty set. Two distinct disjointed of a sum type are not equivalent and I’m not sure how I can write the proper `MakeComparable`

to make this work. Setting it to `-1`

also caused the same bug (not for this particular Set, but a different set of keys).