Some more code that might be of interest to someone. Based on a suggestion by Alistair Turnbull, I've written a Haskell implementation of a randomly balanced binary tree. This merges tree updates with a stream of random numbers, which are used to shuffle the order of nodes in the tree so that it remains balanced. The code is posted together with a short explanation here: http://codepoetics.com/poetix/index.php?p=72 I would be especially interested in any suggestions relating to optimisation. Dominic