while

[macro] while test body ...

1. Evaluates test. If it's nil, returns nil.
2. Evaluates body ...
3. Goto 1.

(mac while (test . body)
  (w/uniq (gf gp)
    `((rfn ,gf (,gp)
        (when ,gp ,@body (,gf ,test)))
      ,test)))