Hi everyone. I have noticed a very strange behaviour for GADTs when using pattern matching. Consider the following type and function :

```
type _ t =
| A : int t
| B : int t
| C : char t
let f : type a. a t -> (a -> string) = function
| A -> string_of_int
| B -> string_of_int
| C -> String.make 1
```

Then the function works and it compiles. However, when combining the match cases of the same type for a syntactic sugar purpose…

```
let g : type a. a t -> (a -> string) = function
| A | B -> string_of_int
| C -> String.make 1
```

… I’m getting this error :

```
Error: This pattern matches values of type int t
but a pattern was expected which matches values of type a t
Type int is not compatible with type a
```

I’m using OCaml 4.07.0. Is that a known bug for this OCaml version, or is it something normal coming from the GADT type system that is a bit different from the classic one ? Thanks for explanations.