Hi everyone, I wrote a simple program that returns the n-th prime number when given n as its command-line argument: import System.Environment isPrime n | n < 2 = False | n == 2 = True | otherwise = not $ any (`divides` n) dividerList where a `divides` b = b `mod` a == 0 dividerList = 2:[3, 5 .. floor $ sqrt $ fromIntegral n] primes = filter isPrime [1 ..] main = do [arg] <- getArgs print $ primes !! (read arg) I compiled it with "ghc -O2". As expected, it runs in constant space, i. e. space complexity O(1). Then, I added the declaration: "primes :: [Int]", expecting a performance improvement. Runtime was indeed reduced by about 50%. However, it no longer runs in constant space. Memory usage rises significantly for arguments > 1e5. I tried all sorts of strictness annotations, which did not help. Turning on profiling with "ghc -O2 -prof -auto-all" made the problem disappear, so I could not analyze the memory leak using the profiler. Only if I remove the cases "n < 2" and "n == 2" from the definition of isPrime, does the program run in constant space with type Int. If I replace the guards by an if statement or pattern matching, the problem remains. I have no idea how to continue from here. Can anyone explain why going from type Integer to Int causes a different space complexity? How would I have to change the program to get it to run in constant space with type Int? I used ghc 7.4.1. Regards, Andreas