On Thu, Mar 4, 2010 at 8:32 AM, Daniel Fischer
<daniel.is.fischer@web.de> wrote:
Am Donnerstag 04 März 2010 04:20:05 schrieb Louis Wasserman:
> James,
>
> Which version of Control.Monad.State are you importing?
>
> If you're just importing vanilla Control.Monad.State, that's actually
> sending you to Control.Monad.State.Lazy.
>
> Using Control.Monad.State.Strict might solve your problems, srsly.
> Laziness can result in epically failing memory leaks.
That was my first thought too, but for this code, Control.Monad.State.Lazy
is the better choice. Control.Monad.State.Strict doesn't play too well with
sequence (and hence mapM). Since James consumes the list of chain lengths
as it is produced (key = maximum keys), no large thunks can build up. With
the strict State, he can't start to look for the maximum until all chain
lengths have been computed, building a big fat thunk for the list.