G(S) {S,D} {0,1,2,3,4,5,6,7,8,9,+,-}S->SDS|SSD->+|-S->0|1|2|3|4|5|6|7|8|9
G[S]:S->S+D|S-D|DD->0|1|2|3|4|5|6|7|8|9
文法是什么？？？
