I did some experiments and now suspect that the culprit is the infinite list. When I replace rmat with
rmat n = listArray ((1,1),(n,n)) [1..] -- no longer random , print (m ! (300, 300)) where m = rmat 800 fails again.
However, if I use a finite list as the second argument of listArray:
rmat n = listArray ((1,1),(n,n)) [1..(n*n)] , then the program runs without problems.
This definition works as well as oleg's.
rmat n = listArray ((1,1),(n,n)) $!! (take (n*n) $ map ct (randoms (mkStdGen 1) ::[Bool]) ) where ct True = Unknown ct False = Dead
I think: If the list is infinite, listArray doesn't return an array as data. Each time an element of the array is used, the list is evaluated. This lazy evaluation require some stack(and the access time cannot be constant?). Is it correct? Thank you.