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

[Andrew Martin]

The way I understand it is more like: they should be Mutual inverses if the type has fewer inhabitants than Int does, and otherwise, just kind of do the best you can. What about the instance for Integer? 

Sent from my iPhone

> On Jun 2, 2018, at 1:39 AM, Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> 
>> On Fri, Jun 01, 2018 at 10:21:45PM +0200, MarLinn wrote:
>> 
>>> Sorry, could you explain further?  I don't understand what the
>>> implementation of any of those proposed instances is supposed to be.
>> 
>> Sure.
> [...]
>> Hope it's clearer now what I meant.
> 
> It's clearer what you meant, but I always assumed that fromEnum and toEnum
> must be mutually inverse.  I can't see that law written anywhere in the docs
> but it seems to be an almost useless class without that assumption.  The
> default implementations of the other methods seems to be completely based on
> that assumption, for example:
> 
>    http://hackage.haskell.org/package/base-4.11.1.0/docs/src/GHC.Enum.html#Enum
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