'while' loop on mutable arrays causes stack overflow

Hello, a friend and I were recently experimenting with mutable arrays. We tried to implement a simple dot product on STUArrays using a 'while' loop. Unfortunately, every implementation we produced caused a stack overflow. Switching to other implementations of 'while' or to IOUArrays did not help us. We were using ghc-6.4.1 on Linux x86, with gcc 3.3.6. It runs perfectly, and is actually quite fast, when we increase the stack space. :)

import Control.Monad.ST import Data.STRef import Data.Array.ST import Control.Monad.Fix import Control.Monad

while :: STRef s Bool -> ST s () -> ST s () while b c = readSTRef b >>= \v -> when v (c >> while b c)

dot :: STUArray s Int Double -> STUArray s Int Double -> ST s Double dot x y = do let (l,r) = bounds x a <- newSTRef 0.0 e <- newSTRef l b <- newSTRef True while b (do ev <- readSTRef e av <- readSTRef a xe <- readArray x ev ye <- readArray y ev writeSTRef b (ev

main = do let d = runST (do x <- newArray (1, 1000000) 1.0 y <- newArray (1, 1000000) 2.0 dot x y) putStrLn $ show d

Unfortunately, I did not keep every 'while' implementation we tried, just this one:

while b c = fix (\d -> readSTRef b >>= (\v -> if v then c >> d else return ()))

We also changed the 'dot' code to use a 'for' loop instead, using IOUArrays in this case:

for :: Int -> IO () -> IO () for 0 c = return () for n c = c >> for (n-1) c

Needless to say, it did not help. Any hints why the stack overflows would be greatly appreciated. Thanks, Gunnar.