[Haskell-beginners] FlexibleInstances
Brent Yorgey
byorgey at seas.upenn.edu
Mon Nov 25 10:43:20 UTC 2013
On Sun, Nov 24, 2013 at 10:02:21PM +0000, AntC wrote:
> > Emanuel Koczwara <poczta <at> emanuelkoczwara.pl> writes:
>
> He Emanuel, you're doing well.
> Hardly anyone these days sticks to Haskell 98;
> and really there's no need to.
> (What you're trying to do can be achieved with H98,
> but would need some not-so-user-friendly coding.)
>
> >
> > I want to enable "instance [Char] where..." but disable "instance [a]
> where...". Is it possible?
> >
>
> Yes, you're almost there.
> You do need FlexibleInstances to be able to put [Char].
>
> To ban [a], you need to ban overlapping instances.
> {-# LANGUAGE NoOverlappingInstances #-}
>
> (Usually overlapping instances is on by default.)
No, it's not.
-Brent
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