Yeah. I considered that, if the function is parameterised by the type of value, you could have a meta-type, but I didn't expect to think of anything neat. Thinking about it, the tricky (but not very efficient) way would be to have a vector (or any other container type) containing value (assuming python doesn't support vectors nested infinitely deep :))

But "not" is very good. Are there any weird edge cases? :)

It doesn't fix the NaN <> NaN problem :-)