public int SumOperation(Expression l, Expression r) { return l.eval() + r.eval(); }
public int MultOperation(Expression l, Expression r) { return l.eval() * r.eval(); }
public int DiffOperation(Expression l, Expression r) { return l.eval() - r.eval(); }
public int DivOperation(Expression l, Expression r) { return l.eval() / r.eval(); }
public BinaryExpression(Token t, Expression left, Expression right) { base.token = t; Left = left; Right = right; }