allegroserve :princ idea extended to :format

I think using :format similarly to :princ et al makes sense.  Features
like ~(, ~{, seem very handy.

I submit the following code.

;; This software is Copyright (c) University of Southern California,
;; 2002-05-09.
;; University of Southern California grants you the rights to distribute
;; and use this software as governed by the terms
;; of the Lisp Lesser GNU Public License
;; (http://opensource.franz.com/preamble.html),
;; known as the LLGPL.

(in-package :net.html.generator)

(defun format-http (fmt &rest vals)
  ;; formatted output the given value to the http stream
  (apply #'format *html-stream* fmt vals))

(def-special-html :format
    #'(lambda (ent args argsp body)
	(declare (ignore ent args argsp))
	`(progn (format-http ,@body)))
  #'(lambda (ent cmd args form stream)
      (declare (ignore ent args))
      (assert (>= (length form) 2))
      (if* (eq cmd :full)
	 then (progn
		(apply #'format stream (cdr form)))
	 else (error ":format must be given format specifier")))
  )

(defun format-safe-http (fmt &rest vals)
  ;; escaped formatted output the given value to the http stream
  (emit-safe *html-stream* (apply #'format nil fmt vals)))

(def-special-html :format-safe 
    #'(lambda (ent args argsp body)
	(declare (ignore ent args argsp))
	`(progn (format-safe-http ,@body)))
  #'(lambda (ent cmd args form stream)
      (declare (ignore args ent))
      (assert (>= (length form) 2))
      (if* (eq cmd :full)
	 then (emit-safe stream 
			 (apply #'format nil (cdr form)))
	 else (error ":format-safe must be given format specifier"))))