[Haskell-cafe] Instance deriving for Void types.

[Tom Ellis]

On Tue, Oct 29, 2013 at 04:31:49AM +0000, AntC wrote:
> > Lyndon Maydwell <maydwell <at> gmail.com> writes:
> > 
> > I was wondering if it's possible to have automatic deriving
> > for some classes for the Void type. ...
> 
> Hi Lyndon, I'm struggling to see any use case for that.
> 
> You'd 'achieve' `show (undefined :: Nada)` crashing your program at run-
> time; rather than failing to compile (if you didn't have the instance).
> 
> Just bite the bullet and give your Void type a constructor.

It was considered a worthwhile enough idea to add a Show instance to the
"void" package

    http://hackage.haskell.org/package/void-0.6.1/docs/Data-Void.html

(where the instance was written by hand, of course, not derived).

Lyndon: perhaps

    import Data.Void
    
    newtype Nada = Nada Void deriving (Show)

will suit you use case.

Tom