Use character range for integral rule

xcsp-lang.lisp

@@ -6,7 +6,7 @@
 
 ;;; "lcsp-xcsp-lang" goes here.
 
-(defrule integral (and (? #\-) (+ (or #\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9)))
+(defrule integral (and (? #\-) (+ (character-ranges (#\0 #\9))))
   (:text t)
   (:function parse-integer))