parser.c

编译原理的词法分析器

#include"global.h"
int lookahead;
parse()  //分析并翻译表达式列表
{
	lookahead = lexan();
	while(lookahead !=DONE){
		expr();/*emit(DONE,DONE);*/match(';');
	}
}
expr()
{
	int t;
	term();
	while(1)
		switch(lookahead){
		case '+':case'-':
			t = lookahead;
			match(lookahead);term();emit(t,NONE);
			continue;
		default:
			return;
	}
}
term()
{
	int t;
	factor();
	while(1)
		switch(lookahead){
		case '*': case '/': case DIV: case MOD:
			t = lookahead;
			match(lookahead);factor();emit(t,NONE);
			continue;
		default:
			return;
	}
}
factor()
{
	switch(lookahead){
	case '(':
		match('(');expr();match(')');break;
	case NUM:
		emit(NUM,tokenval);match(NUM);break;
	case ID:
		emit(ID,tokenval);match(ID);break;
    default:
		error("syntax error");
	}
}
match(t)
    int t;
{
	if(lookahead == t)
		lookahead = lexan();
	else error("syntax error");
}