Hello David, Friday, February 2, 2007, 12:14:05 AM, you wrote: >> Why is this unsafe? What could go wrong? > ref :: IORef [a] > ref <- newIORef [] it could be easily fixed by disallowing polymorphic types here. if someone really need polymorphism, he can continue to use old trick -- Best regards, Bulat mailto:Bulat.Ziganshin at gmail.com