On Mon, Aug 26, 2013 at 12:05:14PM -0700, Bryan O'Sullivan wrote:
> On Mon, Aug 26, 2013 at 1:46 AM, Niklas Hambüchen <[email protected]> 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.
I don't understand this. The same stack overflow occurs with
tenmil :: Int
tenmil = 10 * 1000 * 1000
main :: IO ()
main = do
list <- replicateM tenmil (return ()) :: IO [()]
list `seq` return ()
"return ()" is not excessiely lazy, is it? Could you explain further?
Tom
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