gistfile1.cs

class Memoization<T, TResult> {

    internal Memoization (Func<T, TResult> f, IDictionary<T, TResult> d)
    {
       Invoke = f;
       Values = d;
    }

    public Func<TResult> Invoke {get; private set;}
    public IDictionary<T, TResult> Values {get; private set;}
}

static class FuncCoda {
    public static Memoization<T, TResult> Memoize (this Func<T, TResult> self, IDictionary<T, TResult> cache = null)
    {
        cache = cache ?? new ConcurrentDictionary<T, TResult>();
        Func<T, TResult> c = v => {
            TResult r;
            if (cache.TryGetValue (v, out r))
               return r;
            cache.Add (v, r = self (v));
            return r;
        };
        return new Memoization<T, TResult>(c, cache);
    }
}