Nitpick. This is not a good definition (valid, but not good). The problem is something like this:
(double (prn 3))
Try the above in your repl after entering the mac definition; then consider what must be done in order to protect the x. For example, you might notice that the macros in arc.arc have a lot of (w/uniq (...) `(let ...)) forms, even the arguably simpler ones.
