Operator.cs

using System;

namespace PolishForm
{
    public abstract class Operator : IComparable<Operator>
    {
        public enum Associativity
        {
            Left,   // all parentheses are closed to the left
            Right   // all parentheses are closed to the right
        }

        public readonly char symbol;
        readonly int precedence;
        public readonly Associativity associativity;

        public Operator(char symbol, int precedence, Associativity associativity)
        {
            this.symbol = symbol;
            this.precedence = precedence;
            this.associativity = associativity;
        }

        // Compare operators based on their precedence
        public int CompareTo(Operator? other)
        {
            ArgumentNullException.ThrowIfNull(other);

            return precedence.CompareTo(other.precedence);
        }
        public static bool operator <=(Operator left, Operator right) => left.CompareTo(right) <= 0;
        public static bool operator >=(Operator left, Operator right) => left.CompareTo(right) >= 0;
        public static bool operator <(Operator left, Operator right) => left.CompareTo(right) < 0;
        public static bool operator >(Operator left, Operator right) => left.CompareTo(right) > 0;
    }
}