6ffb02d9f6
This gives us errors with annotated context like this:
```
Error:
× type error: Unknown variable 'x'
╭─[isle_examples/let.isle:24:1]
24 │ (Lower (B.B z))
25 │ (A.Add x y))
· ┬
· ╰── Unknown variable 'x'
╰────
```