Hi. In the "help optimizing memory usage for a program" I discovered some interesting things: 1) Using lazy ByteStrings to read files it not a good choice, since the garbage collector is not able to proper garbage cleanup. Running with -F1 RTS flag, however, keeps memory usage down. 2) UArr from uvector leaks memory. I'm rather sure about this. In fact the memory usage of my program is 815 MB, when: - I use lazy ByteString with -F1 flag or - if I use strict ByteString Using UArray and strict ByteString, memory usage is 660 MB. In total I have 17770 arrays, so there is a leak of about 9146 bytes per array. In another program, where I do a lot of array concatenations, memory leak is much more evident. Even using -F1 flag, memory usage grows too much. Is this a know bug? How can I verify if it is really a memory leak bug? pumpkin_ (on #haskell.it) suggested me to use a more recent version of uvector package, from http://patch-tag.com/publicrepos/pumpkin-uvector Using this version memory usage is, finally, 643 MB! (and execution if a bit faster, too). The other program, with a lot of array concatenations, still eats a lot of memory... Thanks Manlio Perillo