[Haskell-cafe] Why does this work: 'instance Num (Show a) where'

[Tom Ellis]

No, this is in an otherwise empty file.

On Tue, Nov 04, 2014 at 08:46:08PM +1100, Ivan Lazar Miljenovic wrote:
> Is there a corresponding Show datatype?
> 
> At least with 7.8.3, having just that line gives the following error:
> 
> The first argument of ‘Num’ should have kind ‘*’,
>       but ‘Show a’ has kind ‘Constraint’
>     In the instance declaration for ‘Num (Show a)’
> 
> On 4 November 2014 19:30, Tom Ellis
> <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> > This is accepted by GHC 7.6.3.  Is this a bug?  What does it mean?
> >
> >     instance Num (Show a) where