Hi. I have implemented a generalized shuffle function, for the random-shuffle package http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-shuffle I have not yet commited the change, before that I would like to receive some feedbacks (especially by the original author of the shuffle function, in Cc) The new function is defined in this example: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2808 Note that it make use of functions not exported by the System.Random.Shuffle module. I have generalized the original shuffle function in two ways: 1) It is now possible to obtain a random "sample" from a sequence, by doing, as an example: shuffles [1..10] [2, 3, 4, 2, 1] Note that this is equivalent at taking the first 5 elements of the full shuffled sequence, and the performance are pratically the same. 2) It is now possible to pass an infinite "r-sequence" to the shuffle function, as an example: shuffles [1..10] $ cycle [9, 8 .. 1] The result is an infinite list, with elements cyclically extracted from the "r-sequence". When the "r-sequence" contains random numbers, we get an infinite sequence containing all possible random "choices" of elements in the original sequence. Why I'm doing this? The reason is that in a project I need to extract random elements from a list (and I need to extract a lot of them), and using "normal" methods [1] seems to be rather inefficient. Using the `shuffles` function should be much more efficient, since it uses a tree, and this tree is built only once. [1] by normal method I mean: extract a random number, in the range [0, n] (where n is the length of the sequence), and get the element indexed by that number. Indexing for a list if very expensive. And it is not very fast, even using arrays (unless you use non portable unsafeRead). Thanks Manlio Perillo