parser.c

C写的语法分析 递归了程序法语法分析 来自龙书

#include "global.h"

int lookahead;

parse()
{
        lookahead = lexan();
        while(lookahead != DONE)
        {
            expr();
            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(int t)
{
    if(lookahead == t)
    {
        lookahead = lexan();
    }
    else
    {
        error("syntax error");
    }
}