correct behavior of blank curlies

brag/rules/parser.rkt

@@ -168,18 +168,20 @@
                         [(list all min range? max) (let* ([min (if min (string->number min) 0)]
                                                           [max (cond
                                                                  [(and range? max) (string->number max)]
-                                                                 [(and (not range?) (not max)) min] ; {3} -> {3,3}
+                                                                 [(and (not range?) (not max)) (if (zero? min)
-                                                                 [else #f])])
+                                                                                                   #f ; {} -> {0,}
-                                                     (cons min max))]))]
+                                                                                                   min))] ; {3} -> {3,3}
-                [else (raise-argument-error 'grammar-parse "unknown repetition operator" $2)]))
+[else #f])])
-        (pattern-repeat (position->pos $1-start-pos)
+(cons min max))]))]
+[else (raise-argument-error 'grammar-parse "unknown repetition operator" $2)]))
+(pattern-repeat (position->pos $1-start-pos)
                 (position->pos $2-end-pos)
                 min-repeat max-repeat $1
                 #f))]
-     [(atomic-pattern)
+[(atomic-pattern)
  $1]]
     
-    [atomic-pattern
+[atomic-pattern
  [(LIT)
   (pattern-lit (position->pos $1-start-pos)
                (position->pos $1-end-pos)
@@ -220,7 +222,7 @@
                   'splice))]])
    
    
-   (error (lambda (tok-ok? tok-name tok-value start-pos end-pos)
+(error (lambda (tok-ok? tok-name tok-value start-pos end-pos)
          ((current-parser-error-handler) tok-ok? tok-name tok-value (position->pos start-pos) (position->pos end-pos))))))
 
 ;; relocate-pattern: pattern -> pattern