Proposal: Remove Show and Eq superclasses of Num

[Edward Kmett]

+1 from me.

The primary concern is of course that this means loss of compatibility with the current Haskell Report.

foo :: Num a => a -> String
foo = show

would cease to type check.

-Edward

Sent from my iPad

On Sep 15, 2011, at 6:58 PM, Ian Lynagh <igloo at earth.li> wrote:

> 
> Hi all,
> 
> I would like to propose that we remove the Show and Eq superclasses from
> Num, i.e. change
>    class  (Eq a, Show a) => Num a  where
>        [...]
> to
>    class  Num a  where
>        [...]
> 
> 
> The first 2 attached patches (for base and ghc respectively) remove the
> Show constraint. I'm not aware of any justification for why this
> superclass makes sense.
> 
> 
> The next 2 patches (for base and unix respectively) remove the Eq
> constraint. Here's there's some justification in the superclass, as it
> makes
>    f 5 = ...
> work for any Num type, rather than also needing an Eq constraint, but
> personally I would be in favour of removing this superclass too.
> Noteworthy is that Bits now needs an Eq superclass for the default
> methods for 'testBit' and 'popCount'.
> 
> 
> The fifth patch (for base) is what prompted me to get around to sending
> this proposal. It lets us de-orphan the Show Integer instance.
> 
> 
> Any opinions?
> 
> 
> Suggested discussion deadline: 12th October
> 
> 
> Thanks
> Ian
> 
> <0003-Remove-the-Show-superclass-of-Num.patch>
> <0001-Follow-the-removal-of-the-Show-superclass-of-Num.patch>
> <0004-Remove-the-Eq-superclass-of-Num.patch>
> <0001-Follow-the-removal-of-the-Eq-superclass-of-Num.patch>
> <0005-De-orphan-the-Show-Integer-instance.patch>
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