类C语言的 BNF(backus-Naur Form)文法

program --> stmt* | {stmt*}

stmt --> if-else | dowhile | whiledo |for-stmt| assign

if-else --> if (exp)  stmt  else  stmt 

dowhile  --> do  stmt  while ( exp )

whiledo  --> do  stmt  while ( exp )

for-stmt  --> for ( exp, exp, exp )  stmt 

assign --> id=exp

exp --> [ factor ] op  factor | factor op [factor] | factor 

op --> add | sub | mul | div | equ | grt | less | ge | le | ne

factor --> exp | (exp) |  var | number | function