date.lisp string->dttm failures

In working on a project for home, I needed to parse a long list of
DATE fields from old e-mail files.  There were a few pathologic
entries that caused string->dttm to fail.  These input strings and my
hack are provided below.  I couldn't even begin to guess if such a
changes should be made to date.lisp...it could be that the (unknown)
mailer programs that generated these strings should be outlawed :-).

...
mike
********************
Dr Michael A. Koerber
MIT/Lincoln Laboratory
[email protected]

(defun string->dttm (xx)
  "Parse the string into a date/time integer."
  (declare (simple-string xx))
  (or (string-w3-dttm xx)
      (multiple-value-bind (v0 v1 v2 v3 v4 v5 v6 v7)
          (values-list
           (delete-if (lambda (st)
                        (and (symbolp st)
                             (find (subseq (to-string st) 0 3) +week-days+
                                   :test #'string-equal)))
                      (string-tokens
                       (purge-string (if (< (count #\- xx) 2) xx
                                         ;; kill #\- in yyyy-mm-dd
                                         (substitute #\Space #\- xx :count 2))
                                     ":,/()")
                       :max 9)))

        ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	;; Begin MAK Hack
	;; Fix Y2K problem with some dates
	(cond
	 ((and (>= v2 50)
	       (< v2 99)) (incf v2 1900))
	 ((and (>= v2 0)
	       (< v2 50)) (incf v2 2000)))

	;; And some pathological formats give the TIME ZONE as, e.g.,
	;; Wed, 31 Oct 2001 17:59:31 -0800 (PST)
	;;                           ^^^^^ ^^^^ which puts (PST) in v7
	;; and v7 is assumed to be minutes in INFER-TIMEZONE
	(if (not (numberp v7)) (setf v7 nil))
	;; End MAK Hack
        ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	
	
        (if (numberp v0)
            (encode-universal-time (round (or v5 0)) (or v4 0) (or v3 0)
                                   (min v0 v2) (infer-month v1) (max v0 v2)
                                   (infer-timezone v6 v7))
            (encode-universal-time (round (or v4 0)) (or v3 0) (or v2 0)
                                   v1 (infer-month v0) v5
                                   (infer-timezone v6 v7))))))



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