Script Engine Implemented by C# and Regular Expression

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

namespace Zadesoft.Library.Script.Functions
{
    class BuiltInFunctions
        : IFunctionExecutor
    {
        private static BuiltInFunctions _current = new BuiltInFunctions();

        public static IFunctionExecutor Current
        {
            get
            {
                return _current;
            }
        }

        private Dictionary<string, IFunction> _functions;

        protected BuiltInFunctions()
        {
            _functions = new Dictionary<string, IFunction>();
            Init();
        }

        private void Init()
        {
            IFunction fn = new IsTodayFunction();
            _functions.Add(fn.Name, fn);

            fn = new IsBeforeTodayFunction();
            _functions.Add(fn.Name, fn);

            fn = new IsAfterTodayFunction();
            _functions.Add(fn.Name, fn);

            fn = new IsNullOrEmptyFunction();
            _functions.Add(fn.Name, fn);

            fn = new DoesMatchRegexFunction();
            _functions.Add(fn.Name, fn);

            fn = new DoesContainWordFunction();
            _functions.Add(fn.Name, fn);
        }

        public void Register(IFunction fn)
        {
            if (fn != null)
            {
                if (_functions.ContainsKey(fn.Name))
                {
                    _functions[fn.Name] = fn;
                }
                else
                {
                    _functions.Add(fn.Name, fn);
                }
            }
        }

        #region IExternalFunctionExecutor Members

        public bool Contains(string fnName)
        {
            return _functions.ContainsKey(fnName);
        }

        public object Execute(string fnName, params object[] paras)
        {
            if (_functions.ContainsKey(fnName))
            {
                return _functions[fnName].Execute(paras);
            }
            else
            {
                throw new ExpressionException("no such function found in built in functions");
            }
        }

        #endregion

        #region IRuntimePortal Members

        public string Name
        {
            get { return "BuiltInFunctions"; }
        }

        #endregion
    }
}