Numeric literals

Simon Marlow
Wed, 29 Aug 2001 17:33:10 +0100

> On Tue, 28 Aug 2001, Simon Marlow wrote:
> (snip)
> > In GHC, you can do this:
> >=20
> >    import Exception
> >=20
> > 	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;=20
> 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. =20

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.