xml in fptools?
simonmarhaskell at gmail.com
Fri May 26 06:52:34 EDT 2006
Duncan Coutts wrote:
> On Thu, 2006-05-25 at 16:41 -0700, Ashley Yakeley wrote:
>>Malcolm Wallace wrote:
>>>Oh, I always assume lazy I/O. It is one of the most useful parts of
>>>Haskell, and I rely on it all the time for both interactivity and
>>>avoidance of space problems.
>>Lazy I/O is problematic and probably a bad idea for libraries:
> Assuming we do have imprecise exceptions what is wrong with lazy IO?
I'm not even certain that lazy I/O doesn't upset referential
transparency. It seems hard to construct a concrete counter example
though. My intuition is something like this: if evaluating a thunk can
cause IO to take place, then the act of evaluating that thunk might
affect the value of another lazy I/O computation, and hence it should be
possible to get different results by evaluating the thunks in a
different order. I'm concerned that in the presence of dependencies
between lazy I/O computations, the order of evaluation might be visible.
There have been several discussions on this topic, not everyone shares
my views :-) eg.
Actually, in a way I really hope I'm wrong. I would love to use lazy
I/O, but I believe we need to have a good story for error handling and
possible evaluation-order issues first.
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