On Mon, Aug 26, 2013 at 1:46 AM, Niklas Hambüchen <mail@nh2.me> wrote:

This is because sequence is implemented as

sequence (m:ms) = do x <- m
xs <- sequence ms
return (x:xs)

and uses stack space when used on some [IO a].

This problem is not due to sequence, which doesn't need to add any strictness here. It occurs because the functions in System.Random are excessively lazy. In particular, randomIO returns an unevaluated thunk.