/**** parser.c ********************************************/

#include "global.h" 
int lookahead;

parse ( ) { 	/*parses and translates expression list */
    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");
}