Lecture No. 15

Dated: 25-03-2025

bool Expr::isPresent() {
    Term* op1 = new Term(s);
    if (!op1->isPresent()) {
        return false;
    }
    tree = op1->AST();
    Eprime* op2 = new Eprime(s, tree);
    if (op2->isPresent()) {
        tree = op2->AST();
    }
    return true;
}

bool Eprime::isPresent() {
    int op = s->nextToken();
    if (op == PLUS || op == MINUS) {
        s->advance();
        Term* op2 = new Term(s);
        if (!op2->isPresent()) {
            syntaxError(s); 
        }
        TreeNode* t2 = op2->AST();
        tree = new TreeNode(op, exprSofar, t2);
        Eprime* op3 = new Eprime(s, tree);
        if (op3->isPresent()) {
            tree = op3->AST();
        }
        return true;
    }
    else return false; 
}

bool Term::isPresent() {
    Factor* op1 = new Factor(s);
    if (!op1->isPresent()) {
        return false;
    }
    tree = op1->AST();
    Tprime* op2 = new Tprime(s, tree);
    if (op2->isPresent()) {
        tree = op2->AST();
    }
    return true;
}

bool Tprime::isPresent() {
    int op = s->nextToken();
    if (op == MUL || op == DIV) {
        s->advance();
        Factor* op2 = new Factor(s);
        if (!op2->isPresent()) {
            syntaxError(s);
        }
        TreeNode* t2 = op2->AST();
        tree = new TreeNode(op, exprSofar, t2);
        Tprime* op3 = new Tprime(s, tree);
        if (op3->isPresent()) {
            tree = op3->AST();
        }
        return true;
    }
    else return false;
}

bool Factor::isPresent() {
    int op = s->nextToken();
    if (op == ID || op == NUM) {
        tree = new TreeNode(op, s->tokenValue());
        s->advance();
        return true;
    }
    if (op == LPAREN) {
        s->advance();
        Expr* opr = new Expr(s);
        if (!opr->isPresent()) {
            syntaxError(s);
        }
        if (s->nextToken() != RPAREN) {
            syntaxError(s);
        }
        s->advance();
        tree = opr->AST();
        return true;
    }
    return false;
}