Ok, this is actually ambiguous.

switch n {
| n => n | 1
      // ^ Is this an or-pattern or binary expression?

This is tricky because we don't force a delimiter at the end of the pattern (like , in Rust)

We can put it in a new region to avoid ambiguity

switch n {
| n => { n | 1 }
// or....
| n => ( n | 1 )

The problem is that our formatter actively tries to wipe it out.

Maybe reviving local open syntax would help to deal with this kind of ambiguity