FW: 7.4.1-pre: Show & Integral

[Iavor Diatchki]

Hello,

The discussion on the libraries list is archived here:
http://www.haskell.org/pipermail/libraries/2011-September/016699.html

There hasn't been a corresponding discussion for Haskell Prime so,
technically, GHC deviates from the standard.

-Iavor


On Fri, Dec 23, 2011 at 9:41 AM, Simon Peyton-Jones
<simonpj at microsoft.com> wrote:
> I'm confused too.  I'd welcome clarification from the Haskell Prime folk.
>
> S
>
> -----Original Message-----
> From: Serge D. Mechveliani [mailto:mechvel at botik.ru]
> Sent: 23 December 2011 17:36
> To: Simon Peyton-Jones
> Subject: Re: 7.4.1-pre: Show & Integral
>
> On Thu, Dec 22, 2011 at 08:14:54PM +0000, Simon Peyton-Jones wrote:
>> |  2011/12/22 Edward Kmett <ekmett at gmail.com>:
>> |  > The change, however, was a deliberate _break_ with the standard that
>> |  > passed through the library review process a few months ago, and is now
>> |  > making its way out into the wild.
>> |
>> |  Is it reasonable to enquire how many standard-compliant implementations
>> |  of Haskell there are?
>>
>> Just to be clear, the change IS the standard.  GHC has to change to be compliant.
>> At least that's how I understand it.
>
>
> I am confused.
> I am looking now at the on-line specification of  Haskell-2010,
> 6.3 Standard Haskell Classes.
> It shows that  Integral  includes  Show:
>
>                           Eq     Show
>                             \   /
>                              Num
>                              |
>                       Enum  Real
>                          \   |
>                           Integral
>
> This is also visible in the further standard class declarations in this chapter.
>
> Hence, for  `x :: Integral a => a'  it is correct to write  (shows x "").
> And  ghc-7.4.0.20111219  does not allow this.
> So,  ghc-7.4.0.20111219  breaks the 2010 standard. Now, Edward Kmett writes that
> this break is done deliberately.
>
> Am I missing something?
>
> I witness this for the first time: that GHC deliberately breaks the current
> Haskell standard.
> Probably, many people (as myself) dislike this point of the standard.
> Well, they can write a dummy Show implementation for their type T:
>      showsPrec _ _ = showString "(<t> :: T)",
>
> and wait for an improved standard, say, Haskell-II
> -- ?
>
> Regards,
>
> ------
> Sergei
> mechvel at botik.ru
>
>
>
>
>
>
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