Case insensitive intern

intern.lisp

(defun my-intern (s &rest package)
  (declare (type string s)
	   (type symbol package)
	   (optimize (debug 0) (speed 3) (safety 0)))
  (let ((readtable-case (readtable-case *readtable*)))
    (apply #'intern (case readtable-case
		    ((:upcase) (string-upcase s))
		    ((:downcase) (string-downcase s))
		    ((:preserve) s)
		    ((:invert) ;; lazy..
		     (error ":invert is not supported")))
	   package)))