DavidA wrote:
I'm trying to write some code which involves lots of matrix multiplications, but whenever I do too many, I get stack overflows (in both GHCi 6.4.2, and Hugs May 2006).
By placing a couple of strictness annotations, your test' gives the expected answer (given some time) on Hugs. GHCi unfortunately runs into some kind of bug (it says so itself), an unimplemented opcode. The test'' below gives that bug instantly... import List (transpose) -- not needed here -- foldl' f z [] = z -- foldl' f z (h:t) = (foldl' f $! f h z) t -- sum' l = foldl' (+) 0 l map' f [] = [] map' f (h:t) = scons (f h) (map f t) -- strict cons. Could be associated with an infix op, e.g., :$ scons :: a -> [a] -> [a] scons x l | x `seq` l `seq` False = undefined scons x l = x:l u <.> v = sum $ zipWith (*) u v a <<*>> b = multMx a (transpose b) where multMx [] _ = [] multMx (u:us) bT = scons (map' (u <.>) bT) (multMx us bT) id3 = [[1,0,0],[0,1,0],[0,0,1]] -- test = iterate (<<*>> id3) id3 !! 1000000 iterate' f x = x : seq x' (iterate' f x') where x' = f x test' = iterate' (<<*>> id3) id3 !! 1000000 test'' = head $ drop 1000000 $ iterate' (<<*>> id3) id3