FuncExtentions.cs

using System.Collections.Generic;

namespace System
{
    public static class FuncExtentions
    {
        public static Func<T, TResult> Memoize<T, TResult>(this Func<T, TResult> func)
        {
            var cache = new Dictionary<T, TResult>();
            Func<T, TResult> memoizeFunc =  n =>
            {
                if (cache.ContainsKey(n)) return cache[n];
                var result = func(n);
                cache.Add(n, result);
                return result;
            };

            return memoizeFunc;
        }
    }
}