+(defvar +whitespace-chars+
+ '(#\space #\tab #\newline #\return
+ ;; Tested: sbcl unicode, allegrocl, and clisp use #\no-break_space
+ ;; lispworks uses #\no-break-space
+ ;; sbcl non-unicode doesn't support no break space
+ ;; AllegroCL 8-bit strings don't fail on reading #\no-break_space,
+ ;; but can't represent such a character
+ #+lispworks #\no-break-space
+ #+(or (and sbcl sb-unicode) (and allegro ics) clisp) #\no-break_space
+ )
+ "List of whitespace characters for this lisp implementation.")
+