Fine in theory, but in practice when changes to the Prelude have been made previously, they have indeed affected the haskell98 and haskell2010 packages that have subsequently shipped with ghc.

See for instance:

http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/bugs-and-infelicities.html#haskell-standards-divergence

Num superclasses

The Num class does not have Show or Eq superclasses. You can make code that works with both Haskell98/Haskell2010 and GHC by: [workaround described]

Bits superclasses
The Bits class does not have a Num superclasses. It therefore does not have default methods for the bit, testBit and popCount methods.
You can make code that works with both Haskell2010 and GHC by: [workaround described]

Regards,
    Malcolm

On 23 May, 2013,at 09:23 AM, Edward Kmett <ekmett@gmail.com> wrote:

Note, the haskell98 and haskell2010 packages would be unaffected by this proposal as it stands.

The (repeatedly raised in this thread) Applicative as a superclass of Monad situation on the other hand, sadly does impact them.

-Edward

On Thu, May 23, 2013 at 4:19 AM, Henning Thielemann <lemming@henning-thielemann.de> wrote:

On Thu, 23 May 2013, Simon Peyton-Jones wrote:

So there's a decision-making vacuum for the "GHC HQ" libraries. If that's the case, then the best thing is for GHC HQ to get out of the way!

In the special case of adding Traversable and Foldable to Prelude, it worries me that it is about changing Prelude. I am more relaxed about changes to 'base'. However, since Prelude is part of the Haskell 98 and Haskell 2010 specification, I thought that changing Prelude could also be decided by the Haskell Prime committee.

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