Massimiliano, I had to update your code for it to compile (removed "sequence" from testpdf'. However, I don't see any significant difference in the memory profile of either testpdf or testpdf'. Not sure how you are watching the memory usage, but if you didn't know the option "+RTS -sstderr" will print out useful memory statistics when you run your program. E.g.:
pdf_test.exe +RTS -sstderr
gives: 2,157,524,764 bytes allocated in the heap 246,516,688 bytes copied during GC (scavenged) 6,086,688 bytes copied during GC (not scavenged) 45,107,704 bytes maximum residency (8 sample(s)) 4086 collections in generation 0 ( 0.61s) 8 collections in generation 1 ( 0.67s) 129 Mb total memory in use INIT time 0.02s ( 0.00s elapsed) MUT time 5.83s ( 7.48s elapsed) GC time 1.28s ( 1.45s elapsed) RP time 0.00s ( 0.00s elapsed) PROF time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 7.13s ( 8.94s elapsed) %GC time 18.0% (16.3% elapsed) Alloc rate 369,202,098 bytes per MUT second Productivity 81.8% of total user, 65.2% of total elapsed Above you can see 45 MB was the max amount of memory ever in use - and according to the heap profiling I did it's about constant. I saw the same results when using "testpdf'". A few tricks I've learned to reduce space usage: * Use strict returns ( return $! ...) * foldl' over foldr unless you have to use foldr. * Profile, profile, profile - understand who is hanging on to the memory (+RTS -hc) and how it's being used (+RTS -hb). * Use +RTS -p to understand who's doing all the allocations and where your time is being spent. * Approach profiling like a science experiment - make one change, observe if anything is different, rollback and make another change - observer the change. Keep notes! Good luck! Justin