When I implemented Arc in Lumen (more info on Lumen: http://arclanguage.org/item?id=20935), this technique was ported over naturally. You can play with it here:

  git clone https://github.com/lumen-language/lumen
  git checkout 2018-10-29/arc
  npm i
  rlwrap bin/lumen-node # rlwrap is optional
  > (load "arc.l")
  function
  > (mac awhen (cond . body)
      `(let it ,cond
         (when it ,@body)))
  > (awhen 'hi (print it))
  hi
  > (awhen nil (print 'hi))
  > (awhen 1 (print it))
  1
  > (awhen 1 (print it)
      (let-macro ((awhen (cond . body)
                    `(let it ,cond
                        (unless it ,@body))))
        (awhen false (print it)))
      (awhen 42 (print it)))
  1
  false
  42
  >