[Haskell-cafe] No Enum for (,), no Enum or Bounded for Either

[Tom Ellis]

I made a typo in the second one.  It should be

      instance (Bounded a, Bounded b) => Bounded (Either a b)


On Fri, Jun 01, 2018 at 07:32:55PM +0100, Tom Ellis wrote:
> True.  I think I would propose
> 
>     instance (Bounded a, Bounded b, Enum a, Enum b) => Enum (Either a b)
>     instance (Bounded a, Bounded b) => Enum (Bounded a b)
>     instance (Bounded a, Bounded b, Enum a, Enum b) => Enum (a, b)
> 
> On Fri, Jun 01, 2018 at 02:23:58PM -0400, Li-yao Xia wrote:
> > One issue is that (Int, Int) is too big to define toEnum/fromEnum.
> > 
> > On 06/01/2018 02:10 PM, Tom Ellis wrote:
> > > I'm a bit surprised that whilst `Either` and `(,)` have instances for `Ord`
> > > 
> > > * `(,)` has no instance for `Enum`
> > > * `Either` has no instance for `Enum` or `Bounded`
> > > 
> > > Is there a particular reason for that?  It might be tricky to implement
> > > 
> > >      toEnum :: Int -> a
> > >      fromEnum :: a -> Int
> > > 
> > > but in the presence of `Bounded` that should be possible.
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