Cannot parse variant constructor containing object and fat arrow

```
type queryDelta =
  | Compute(({"blocked_ids": unit}) => unit)
```

Pop this in the formatter and it reformats to

```
type queryDelta = Compute({"blocked_ids": unit} => unit)
```

which gives a syntax error
```
[E] Line 1, column 48:
I'm not sure what to parse here when looking at "=>".
```

Thanks!