//while语句 Stmt Parser::whiles(ifstream &file) { Rel x; Stmt s; While whilenode; match(WHILE, file); match(LPAR, file, Error(3, lex.line)); x = rel(file); match(RPAR, file, Error(4, lex.line)); s = stmt(file); whilenode.init(x, s); whilenode.gen(); return whilenode; }