(defun change-directory (&optional path)
  "Change the current directory to DIR. Defaults to (user-homedir-pathname) ~
if not given."
  (when (not path)
    (setf path (enough-namestring (user-homedir-pathname))))
  (when (pathnamep path)
    (setf path (safe-namestring path)))
  #+openmcl (syscall (chdir path))
  #+sbcl (progn
	   (syscall (chdir path))
	   (let ((tn (ignore-errors (truename path))))
	     (when tn
	       (setf *default-pathname-defaults* tn))))
  #+clisp (ext:cd path)
  #+excl (setf *default-pathname-defaults* (pathname (excl:chdir path)))
  #+cmu (setf (ext:default-directory) path)
  #+ecl
  ;; try to turn it into a directory
  ;;; @@@ this fails for .. or .
  ;;(ext:chdir (if (not (pathname-directory path))
  ;;  (make-pathname :directory `(:relative ,path))
  ;;  (make-pathname :directory path)))
  ;;; try something simpler but os dependent
  (ext:chdir (if (and (stringp path) (length path))
		 (concatenate 'string path "/")
		 path))
  #+lispworks (hcl:change-directory path)
  #+abcl
  (progn
    (syscall (chdir path))
    (setf *default-pathname-defaults* (truename path)))
  #-(or clisp excl openmcl sbcl cmu ecl lispworks abcl)
  (missing-implementation 'change-directory))