On Tue, 28 Aug 2001, Simon Marlow wrote: (snip)
In GHC, you can do this:
import Exception
do result <- catch (evaluate (read "foo" :: Int)) (\error -> ... ) (snip)
I do like that. Is it likely to become standard someday, do you think? Errors like this should certainly be catchable in such a way; I was sad when I was first looking into this and found that 'catch' seemed to be inextricably linked to IO.
Well, we'd like it to become standard :-) The exception stuff is really very easy to implement - you just use the standard stack-unwinding implementation of throw, and catch has to push a special stack frame. GHC's asynchronous exceptions are slightly harder, but I don't think it was more than a day or two's work. As a bonus you get to use a more efficient implementation of the IO monad, because it doesn't have to deal explicitly with exceptions. And then IO becomes a straightforward instance of ST. I guess I should also document the Exception extension in a self contained way, similar to the way the FFI extension is documented. Cheers, Simon