Simon Marlow wrote:
> > Simon Marlow:
> > > [Lazy I/O] is nice, but it introduces too many problems. What
> > > happens to any I/O errors encountered by the lazy I/O? They have to
> > > be discarded, which means you can't effectively use lazy I/O for
> > > robust applications anyway.
> >
> > Surely they are thrown as exceptions which can then be manipulated
> > in pure code using
> >
> > mapExceptions :: (Exception -> Exception) -> (a -> a)
> >
> > and caught in the IO monad using catch?
>
> No, the report clearly states that they are discarded.
Could you please point out where? I couldn't find it with a quick look.
> We could perhaps have our own versions of the lazy I/O operations which
> throw exceptions, but this in itself is problematic because these kind
> of exceptions would be asynchronous in nature. If lazy I/O is allowed
> to raise exceptions, then we have a situation where evaluating anything
> can raise an I/O exception. In theory this shouldn't be a problem - we
> all ought to be writing asynchronous-excpetion-safe code anyway to
> protect against StackOverflow, but an I/O exception is often one that
> you want to handle gracefully and recover from. I feel distinctly
> uncomfortable about I/O exceptions being thrown by pure code, and even
> more uncomfortable about asynchronous I/O exceptions.
Is even the following example from the library report (section 11.8.2)
problematic?
import System
import Char( toUpper )
main = do
[f1,f2] <- getArgs
s <- readFile f1
writeFile f2 (map toUpper s)
-- Dean
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