[Haskell-cafe] How do I avoid stack overflows?

15 Mar 2007

      Hi.

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). The following code exhibits the problem.

import List (transpose)

u <.> v = sum $ zipWith (*) u v

a <<*>> b = multMx a (transpose b)
	where
		multMx [] _ = []
		multMx (u:us) bT = map (u <.>) bT : multMx us bT

id3 = [[1,0,0],[0,1,0],[0,0,1]]

test = iterate (<<*>> id3) id3 !! 1000000

I tried to fix the problem using seq, as follows:

iterate' f x = x : seq x' (iterate' f x') where x' = f x

test' = iterate' (<<*>> id3) id3 !! 1000000

However, in both cases, the code causes stack overflows in both interpreters. 
(It sometimes kills GHCi, which I guess is a bug.)

Any ideas?

Thanks.

[Haskell-cafe] How do I avoid stack overflows?

DavidA