Hi, I have just started using Haskell, and it has been really fun so far. But I have problems with memory usage when handling large files. What I do is the following; I load my file in one chunk, and does a lot of substitutes on the string - this is quick eating all my memory and the computers start to get really slow. The problem is of course that the string is copied each time I do a substitute, and I wonder if a more experienced haskeller has a better solution to my problem. I have myself considered these solutions, but they all seems non-elegant; 1. Use some IO extensions to fake a mutable variable - but solving a problem like this with a solution which is meant for IO does not seem right? 2. Split the file in smaller parts could be a solution, but then I would have to do a lot of preparsing to make sure I not spilt my file in the middle of a pattern. Sounds to me like developing a lex-like system for such a easy task is overkill? 3. I could maybe use some form of mutable arrays, but doing string regexps on an array...? 4. ? Any clues or opinions? Cheers, Petter Egesund