On Sun, 2007-11-18 at 12:11 -0800, Iavor Diatchki wrote:
> Hello,
>
> I was playing around with "bang patterns" and I noticed that
> when combined with asynchronous exceptions they can lead to
> programs where the order of the declarations in a binding
> group is important! Here is an example:
>
> > import Control.Exception
> > import Prelude hiding (catch)
> >
> > main = putStrLn =<< eval_order
> >
> > test = "no exception"
> > where !_ = error "top down"
> > !_ = error "bottom up"
> >
> > eval_order = evaluate test `catch` \e ->
> > case e of
> > ErrorCall txt -> return txt
> > _ -> throw e
>
> Of course, this is a contrived exampled but, as far as I know,
> this was not possible in Haskell before (if anyone has an example
> to the contrary please send it to the list).
>
> By the way, with GHC
6.8.1 the above program prints "bottom up".
> This means that when there are multiple "banged" bindings they
> are evaluated starting with the last one in the text. I imagine
> than in most programs this is not particularly important, but
> it seems to me that it would be a bit nicer if we were to adjust
> the translation so that bindings were evaluated top to bottom
> (e.g., like in ML).