Hi Having written a suffix-array based program using lists, I thought I'd speed it up a bit, and perhaps more importantly, save space, using arrays. Basically, the problem is to sort all suffixes of a string, represented as an array of offsets, alphabetically. (Does anybody have such code? Efficient?) The good news is that space consumption is reduced -- except for a few weird spikes (which makes me suspect there are many of them, living for very short durations), memory use is low. But speed is another issue -- the list based version is a lot faster. Okay, I use UArrays and permute them by (//), and this operation is totally dominant in the profile. Is it correct that GHC is very naive about updating them, and even small updates cost O(n)? Is it better to (//) over few large lists than over many small ones? I'll try a IOUArray next; however, is there anything else I could/should try? I know there has been array sorts implemented previously, are anybody aware of recent results? -kzm -- If I haven't seen further, it is by standing in the footprints of giants