Universal Framework for Science and Engineering - Part 4: Space elevator

using System;
using System.Collections.Generic;
using System.Collections;
using System.Text;

namespace FormulaEditor
{
    /// <summary>
    /// Elementary real variable
    /// </summary>
    public class ElementaryRealVariable : IObjectOperation, IOperationAcceptor, IDerivationOperation,
        IFormulaCreatorOperation
    {
        /// <summary>
        /// Return type
        /// </summary>
        private const Double type = 0;

        /// <summary>
        /// Value
        /// </summary>
        private double? val;

        /// <summary>
        /// Operation symbol
        /// </summary>
        private object symbol;


        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="symbol">Symbol</param>
        /// <param name="type">Type</param>
        public ElementaryRealVariable(object symbol)
        {
            this.symbol = symbol;
        }



        /// <summary>
        /// Creates formula
        /// </summary>
        /// <param name="tree">Operation tree</param>
        /// <param name="level">Formula level</param>
        /// <param name="sizes">Sizes of symbols</param>
        /// <returns>The formula</returns>
        public MathFormula CreateFormula(ObjectFormulaTree tree, byte level, int[] sizes)
        {
            MathFormula form = new MathFormula(level, sizes);
            MathSymbol sym = null;
            if (symbol is Char)
            {
                sym = new SimpleSymbol((char)symbol);
            }
            else if (symbol is StringPair)
            {
                StringPair sp = symbol as StringPair;
                sym = new SubscriptedSymbol(sp.First, sp.Second);
            }
            sym.Append(form);
            return form;
        }

        /// <summary>
        /// Operation priority
        /// </summary>
        public int OperationPriority
        {
            get
            {
                return (int)ElementaryOperationPriorities.Variable;
            }
        }


        /// <summary>
        /// Calculates derivation
        /// </summary>
        /// <param name="tree">The function for derivation calculation</param>
        /// <param name="s">Derivation string</param>
        /// <returns>The derivation</returns>
        public ObjectFormulaTree Derivation(ObjectFormulaTree tree, string s)
        {
            double val = 0;
            if (s.Length == 1)
            {
                if (symbol is Char)
                {

                    if (s[0] == (char)symbol)
                    {
                        val = 1;
                    }
                }
            }
            ElementaryRealConstant op = new ElementaryRealConstant(val);
            return new ObjectFormulaTree(op, new List<ObjectFormulaTree>());
        }


        /// <summary>
        /// Arity of this operation
        /// </summary>
        public int Arity
        {
            get
            {
                return 0;
            }
        }

        /// <summary>
        /// Calculates result of this operation
        /// </summary>
        public object this[object[] x]
        {
            get
            {
                return val;
            }
        }

        /// <summary>
        /// Return type
        /// </summary>
        public object ReturnType
        {
            get
            {
                return type;
            }
        }

        /// <summary>
        /// The "is powered" sign
        /// </summary>
        public bool IsPowered
        {
            get
            {
                return true;
            }
        }



        /// <summary>
        /// Accepts operation
        /// </summary>
        /// <param name="type">Argument type</param>
        /// <returns>The operation</returns>
        public IObjectOperation Accept(object type)
        {
            return this;
        }


        /// <summary>
        /// Sets value
        /// </summary>
        public double? Value
        {
            set
            {
                val = value;
            }
        }

        /// <summary>
        /// Operation symbol
        /// </summary>
        public object Symbol
        {
            get
            {
                return symbol;
            }
        }
    }
}