Hi, I'm starting to learn haskell, and I was considering it for a simulation I've been designing, but I ran into this problem with a simple numerical calculation. The attached program is supposed to solve a stiff differential equation, and you have to use a very small stepsize and lots of steps to resolve the part of the solution near a singularity. It looks to me like this program should run in constant space because the iterate2 function is tail-recursive, but when I run it on hugs or ghc 2.6.1, I get an error that it runs out of stack space on the third calculation. (And the quick fix is to give it a flag that increases the stack, but if I'm to use haskell for a potentially large and long simulation, I can't afford to let it run for three days only to get an error and figure out that it needs more stack space than the computer can give.) I suppose in my ODE example it's building up expressions somewhere for lazy evaluation, so I've tried putting seq and $! in various places. I have another example where using "else seq x (iterate2 ...)" helps, but that doesn't solve my problem here. I've also tried -O but it doesn't help. Can anyone give me some idea as to what to do? Thanks, -wgm iterate2 f x n = if n == 0 then x else iterate2 f (f x) (n - 1) integrate step f xInit xFinal yInit nSteps = let h = (xFinal - xInit) / fromIntegral nSteps next = step f h in iterate2 next (xInit, yInit) nSteps rk4Next f h (x, y) = let a1 = h * f x y a2 = h * f (x + h/2) (y + a1/2) a3 = h * f (x + h/2) (y + a2/2) a4 = h * f (x + h) (y + a3) in (x + h, y + a1/6 + a2/3 + a3/3 + a4/6) rk4 = integrate rk4Next stiff x y = -( ((exp (x - 1)) + (x - 1) * y) / (1 - x - 0.0001 * y) ) main = do putStr "Begin\n" putStr (show (rk4 stiff 0 1 (exp (-1)) 1000)) putStr "\n" putStr (show (rk4 stiff 0 1 (exp (-1)) 10000)) putStr "\n" putStr (show (rk4 stiff 0 1 (exp (-1)) 100000)) putStr "\n" __________________________________ Do you Yahoo!? Yahoo! Mail - You care about security. So do we. http://promotions.yahoo.com/new_mail