I apologise if this is off topic for this list - I haven't been here long. Someone recently mentioned that the MD5 function in GHC uses C code to do the work so returns an IO String rather than a String. I have written an MD5 implementation in pure Haskell code (following the RFC - I don't know if a better optimised version could be written although I may look into this). I've put the code at http://c93.keble.ox.ac.uk/~ian/md5/ License is GPL. Ian