How do I write a generic memoize function?

Question

I\'m writing a function to find triangle numbers and the natural way to write it is recursively:

function triangle (x)
   if x == 0 then return 0 end
   retu         


        

Answer 1

Here is a generic C# 3.0 implementation, if it could help :

public static class Memoization
{
    public static Func Memoize(this Func function)
    {
        var cache = new Dictionary();
        var nullCache = default(TResult);
        var isNullCacheSet = false;
        return  parameter =>
                {
                    TResult value;

                    if (parameter == null && isNullCacheSet)
                    {
                        return nullCache;
                    }

                    if (parameter == null)
                    {
                        nullCache = function(parameter);
                        isNullCacheSet = true;
                        return nullCache;
                    }

                    if (cache.TryGetValue(parameter, out value))
                    {
                        return value;
                    }

                    value = function(parameter);
                    cache.Add(parameter, value);
                    return value;
                };
    }
}

(Quoted from a french blog article)