RE: if (++) were left associative ?

I don't think so. I think it only takes linear time to get the head. But once you've gotten the head, it takes linear time again to get the head of the tail, .... You get (I think...) a progression like n+(n-1)+(n-2)+...+1, which is in O(n^2).

What does 'n' denote? The get the head, it takes time proportional to the number of (++) invocations. Is that what you mean? konst