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

[Ivan Lazar Miljenovic]

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
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Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com