[quiz] [QUIZ 3] reader macro

[Matt Pillsbury]

On Jul 10, 2007, at 11:03 , Larry Clapp wrote:
> Send answers to the list, preferably with at least one working test
> case displayed, e.g. something like

>   cl-user> #"\w \" \s"
>   "\\w \" \\s"

Well, I ended up doing something slightly different.

(defun |#?-READER| (s c n)
   (declare (ignore c n))
   (let ((term (read-char s)))
     (with-output-to-string (string)
       (loop
	 :for char := (read-char s)
	 :until (char= char term)
	 :if (and (char= char #\\)
		  (char=
		   (peek-char nil s)
		   term))
	 :do
	 (write-char (read-char s) string)
	 :else :do
	 (write-char char string)))))

(set-dispatch-macro-character #\# #\? #'|#?-READER|)

This means that whatever character follows the #? becomes the  
delimeter, like so:

CL-USER> #?"foo\"bar"
"foo\"bar"

CL-USER> #?%foo"bar%
"foo\"bar"

CL-USER> #?%foo\\bar%
"foo\\\\bar"

CL-USER> #?%foo\"bar%
"foo\\\"bar"

Cheers,
Pillsy