I was looking for a shuffling algorithm to shuffle mp3-playlists so was very happy to see System.Random.Shuffle: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-shuffle-0.... However I get errors,non-exhaustive patterns in function shufleTree or extractTree depending how I call it. Errors are at the bottom. I fixed it but I don't have the math skills to see if I perhaps broke it statistically ... Here is my fix, someone (don't remember who, helped me a little): http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2789#a2789 the shuffle at the end is with the fix. *Freet> S.shuffle [1..10] [1..3] Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. Loading package random-shuffle-0.0.2 ... linking ... done. [2,4,6*** Exception: src\System\Random\Shuffle.hs:(52,6)-(55,30): Non-exhaustive patterns in function shuffleTree *Freet> S.shuffle [1..3] [1..10] [2,*** Exception: src\System\Random\Shuffle.hs:(66,6)-(79,27): Non-exhaustive patterns in function extractTree *Freet> :load "c:/ghc/ghc-6.10.1/progs/Mp3Player/Shuffle.hs" [1 of 1] Compiling Shuffle ( C:\ghc\ghc-6.10.1\progs\Mp3Player\Shuffle.hs, interpreted ) Ok, modules loaded: Shuffle. *Shuffle> shuffle [1..3] [1..10] [2,1,3] *Shuffle> shuffle [1..10] [1..3] [2,4,6*** Exception: C:\ghc\ghc-6.10.1\progs\Mp3Player\Shuffle.hs:(27,13)-(31,30): Non-exhaustive patterns in function shuffle' *Shuffle> shuffle [1..10] [1..10] [2,4,6,8,10,3,9,7,5,1] *Shuffle>