CORE_ch.bnf

<prog>     ::= 程序 <decl seq> 开始 <stmt seq> 结束
<decl seq> ::= <decl> | <decl> <decl seq>
<stmt seq> ::= <stmt> <stmt seq> | <stmt>
<decl>     ::= int  <id list> ;
<id list>  ::= <id> , <id list> | <id>
<stmt>     ::= <assign>|<if>|<loop>|<output>|<input>
<assign>   ::= <id> 等于 <exp> ;
<if>       ::= 如果 <cond> { <stmt seq> } ;
<loop>     ::= 见鬼 <cond> { <stmt seq> } ;
<input>    ::= 输入 <id list> ;
<output>   ::= 输出 <id list> ;
<cond>	   ::= <comp> | ! <cond> | [ <cond> && <cond> ] | [ <cond> or <cond> ]
<comp>     ::= ( <op> <comp op> <op> )
<exp>      ::= <fac> | <fac> 加 <exp> | <fac> 减 <exp>
<fac>      ::= <op> | <op> 乘 <fac>
<op>       ::= <int> | <id> | ( <exp> )
<comp op>  ::= != | == | < | > | <= | >=
<id>       ::= <let><id> | <let><int> | <let>
<let>      ::= A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z
<int>      ::= <digit><int> | <digit>
<digit>    ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9