Inside the Mathematical Expressions Evaluator

using System;
using System.Text.RegularExpressions;

namespace SevenZ.Calculator
{
   public partial class Calculator
   {
      internal static class Token
      {
         public const string PRight = ")", PLeft = "(", Power = "^", Divide = "/",
                            Multiply = "*", UnaryMinus = "_", Add = "+", Subtract = "-",
                            Sentinel = "#", End = ";", Operand = "@", None = " ";
                            

         static string[] binaryOperators = new string[] { Multiply, Divide, Subtract, 
                                                          Add, Power };
         static string[] unaryOperators = new string[] { UnaryMinus };         

         public static int Precedence(string op)
         {
            switch (op)
            {
               case Subtract:    return 4;
               case Add:         return 4;
               case UnaryMinus:  return 8;
               case Multiply:    return 16;
               case Divide:      return 16;
               case Power:       return 32;
               case PLeft:       return 64;
               case PRight:      return 64;

               default: return 0; //operators END, Sentinel
            }
         }

         #region IsFunctions
         public static bool IsBinary(string op)
         {
            return Contains(op, binaryOperators);
         }

         public static bool IsUnary(string op)
         {
            return Contains(op, unaryOperators);
         }

         public static bool IsDigit(string token)
         {
            return Regex.IsMatch(token.ToString(), @"\d+.?\d*");
         }

         #endregion

         /// <summary>
         /// Converts unary operator from expression to driver-comprehensible mode
         /// </summary>
         /// <param name="op">Unary operator</param>
         /// <returns>Converted operator</returns>
         public static string ConvertOperator(string op)
         {
            switch (op)
            {
               case UnaryMinus: return "_";
               default: return op;
            }
         }

         public static string ToString(string op)
         {
            switch (op)
            {
               case End: return "END";
               default: return op.ToString();
            }
         }
      }

      static bool Contains(string token, string[] array)
      {
         return Array.IndexOf<string>(array, token) != -1;
      }
   }

}