On Nov 30, 2007 2:39 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:

Sebastian Sylvan wrote:
> On Nov 29, 2007 9:10 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:
>
>> How do you avoid accidentally recomputing the list multiple times?
>>
>
> What do you mean? It's exactly the same as your original program but
> with ST instead of IO? Why would it get accidentally recomputed in
> this scenario and not before?
>

Because before the moment when it gets executed relative to the main I/O
thread is explicitly defined, and now it isn't.

Yes it is. There's nothing magical about how the I/O thread guarantees when/in what order things get executed; it all has to do with data dependencies. Since the ST monad represents a strict state thread, it will have exactly the same behavior in terms of when/in what order things get executed as in the IO monad.

-Brent