Re: Functor (Either a)

15 Jul 2007

      Hi Conor,

On Sun, Jul 15, 2007 at 08:20:25PM +0100, Conor McBride wrote:
...
and it does rather suggest that there's an instance of Functor for  
(Either a). Yet,
Prelude> fmap not (Right True)
<interactive>:1:0:
    No instance for (Functor (Either a))
      arising from use of `fmap' at <interactive>:1:0-20
It's in Control.Monad.Instances:

Prelude> :m + Control.Monad.Instances
Prelude Control.Monad.Instances> fmap not (Right True)
Right False

I don't know if there's a way of deducing that from the haddock
documentation.

Thanks
Ian

Re: Functor (Either a)

Ian Lynagh