(defun gen-html-tag (form environment)
  (destructuring-bind (tag &rest body) form
    `(progn (format t "<~A>" ',tag)
            ,@body
            (format t "</~A>" ',tag))))

(setf (macro-function 'a) (function gen-html-tag)
      (macro-function 'p) (function gen-html-tag)
      #| …the whole html…|#)

(with-output-to-string (*standard-output*)
  (p (princ "foo")
     (a (princ "link"))
     (princ "bar")))
#| --> "<p>foo<a>link</a>bar</p>" |#