I have some code which is being unnecessarily lazy (and occupying too much heap space). The code should read and process several files one by one. What's happening is that all files get read in but the processing is delayed by laziness, and the files are being retained. It looks something like this (after simplification): main = do result <- foldM countAFile initialcounts fileNameList prettyprint result countAFile oldcounts filename = do compiledFile <- readAndCompile filename let newcounts = countAssociations compiledFile oldcounts return newcounts I would love to have used CPS, but this seems to force me to lift a huge amount of code into both the IO monad and the CPS, as countAssociations just calls another function, which calls another, and so on. If I change countAFile to use a redundant test to force evaluation of newcounts: countAFile oldcounts filename = do compiledFile <- readAndCompile filename let newcounts = countAssociations compiledFile oldcounts if newcounts == newcounts then return newcounts else error "suitable error message" then the program runs beautifully (if a little slowly), occupying a constant amount of heap. If instead I use a strict data type to store my counts, or use seq, then I get no improvement, and it's just as if I hadn't used them. I understand why a strict data type won't help me, as it's the function calls that are lazy. But what about $! and seq? countAFile oldcounts filename = do compiledFile <- readAndCompile filename let newcounts = countAssociations compiledFile oldcounts return $! newcounts Does anyone understand why $! (or equivalently "seq") have no effect here? Is there a better way to do this? Amanda -- Amanda Clare http://users.aber.ac.uk/ajc99/ Tel: +44 (0)1970 621922 Fax: +44 (0)1970 622455 Dept. of Computer Science, University of Wales, Aberystwyth, SY23 3DB