I'm doing some statistical calculations, and I decided to try this out in Haskell to see how it goes. I'm really enjoying using the language, so I hope I can straighten this out so I can keep using it at work. I keep getting stack overflows, so I think my code must be too lazy somewhere (that's what that means, right?) Here is my code to build random vectors and matrices. ------------------------------------------------------------------------ -------- type Vector = UArray Int Float type Matrix = DiffArray Int Vector -- Generate a random number from the unit interval randomEntry :: State StdGen Float randomEntry = do g <- get (x, g') <- return $ randomR (0,1) g put g' return x -- Build an array of n random things randomArray :: (IArray arr a) => Int -> State StdGen a -> State StdGen (arr Int a) randomArray n x = mapState arr . sequence $ replicate n x where arr (a,s) = (array (1,n) $ zip [1..n] a, s) -- A random vector is an array of random entries randomVector :: Int -> State StdGen Vector randomVector n = randomArray n randomEntry -- a random matrix is an array of random vectors. randomMatrix :: Int -> Int -> State StdGen Matrix randomMatrix i j = randomArray i $ randomVector j ------------------------------------------------------------------------ -------- I decided to write a tester function to see whether building the random matrices is the root of my problem. tester :: Int -> [Matrix] tester n = fst $ runState vals $ mkStdGen 1 where vals = sequence . repeat $ randomMatrix n n Then if I do main = print $ ((tester 10)!!10000)!5 with ghc -O, I get a stack overflow. So all main is trying to do is build an infinite list of 10x10 random matrices, extract the 10000th one, and then look at row 5. Stack overflows like this have given me trouble before. I thought using unboxed arrays might help, since they're forced to be strict, but I haven't had any luck with them. Are there any general guidelines I'm overlooking? I think Haskell can be very useful in my work, but I have to get beyond this hurdle. I just figured out the State monad yesterday, so maybe I'm not using it as it's intended? I dunno. Thanks, Chad Scherrer