The company I work for was gracious enough to allow me to release a haskell program I wrote for them: http://www.isecpartners.com/file_fuzzers.html There's a python version and a rewrite in haskell. I used some looping constructs discussed earlier on this list to keep the haskell code similar to its original python code. Don Stewart was kind enough to help me optimize some of the code using ByteString and a faster PRNG (the System.Random class seems to be a bit on the slow side!). Prior to using ByteString and optimizing the code it was a bit slower than the python version, but with optimizations it is quite a bit faster. (In practice, the external program being invoked is usually the performance bottleneck). Tim Newsham http://www.thenewsh.com/~newsham/