Weird behavior with pattern matching.

```scala
object Foo {
  val (A, B) = () 
}
```
Compiles fine even though neither `A` nor `B` are defined.

```scala
object Foo {
  val (A, b) = ()
}
```
Doesn't compile because `Unbound Identifier Error` (on `A`).

```scala
object Foo {
  val (a, b) = ()
}
```
Doesn't compile because `cannot test if value types are references`.