Elisp when unless

(defmacro when (cond &rest body)
  "If COND yields non-nil, do BODY, else return nil.
When COND yields non-nil, eval BODY forms sequentially and return
value of last one, or nil if there are none.

\(fn COND BODY...)"
  (declare (indent 1) (debug t))
  (list 'if cond (cons 'progn body)))

(defmacro unless (cond &rest body)
  "If COND yields nil, do BODY, else return nil.
When COND yields nil, eval BODY forms sequentially and return
value of last one, or nil if there are none.

\(fn COND BODY...)"
  (declare (indent 1) (debug t))
  (cons 'if (cons cond (cons nil body))))