put curlies into reserved chars

brag/rules/lexer.rkt

@@ -13,8 +13,8 @@
 ;; A newline can be any one of the following.
 (define-lex-abbrev NL (:or "\r\n" "\r" "\n"))
 
-;; chars used for quantifiers & parse-tree filtering
-(define-for-syntax quantifiers "+:*") ; colon is reserved to separate rules and productions
+;; reserved-chars = chars used for quantifiers & parse-tree filtering
+(define-for-syntax quantifiers "+:*{}") ; colon is reserved to separate rules and productions
 (define-lex-trans reserved-chars
   (λ(stx) #`(char-set #,(format "~a~a~a" quantifiers hide-char splice-char))))