[Haskell-cafe] Instance deriving for Void types.

AntC anthony_clayden at clear.net.nz
Tue Oct 29 04:31:49 UTC 2013

> 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.


> I guess the obvious one would be Show.
> data Nada deriving Show
> {*
> instance Show Nada where
>   show _ = undefined
> *}

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