Though I ran into trouble naming my macro with such a short name as "p", as it turned out I also had written a function that took "p" as an argument...
arc> (def foo (p)
(= p!a 'bar))
Warning: Inverting what looks like a function call. (p (quote a)) ((fn () (pr "<p>") (quote a) (pr "</p>")))
#<procedure: foo>
