How we run through `foo ↼ 123`

- `foo` is dereferenced in `locals namespace`; no such name exists, so the
  `namespace` returns an `undefined`, with `the.undefined scope` attached to
  `locals`, and `the.undefined name` attached to the missing name
- `↼` is dereferenced in `the.undefined namespace`; it dereferences to a
  function
- `the.undefined ↼ infix?` is `true`, so we look ahead and deal with `123`
- `123` is a literal, so we don’t have to do anything with it
- We call `the.undefined ↼(123)`
- The implementation of `↼` does something akin to
  `my scope __set(my name, 123)`