Drastic Prelude changes imminent

[Herbert Valerio Riedel]

Lennart,

On 2015-01-28 at 11:14:50 +0100, Augustsson, Lennart wrote:
> I've updated the Wiki page (https://ghc.haskell.org/trac/ghc/wiki/BurningBridgesSlowly)
> with what I think would be a sensible course of actions:

[..]

While I'm still in the process of thinking through the plans/proposals
layed out on that wiki page, I'm somewhat missing what actual problem(s)
those proposals are trying to solve.

What's the actual problem/risk we're running into, if we instead go with
a "Proposal 0" which consists in `base-4.8` as currently implemented in
GHC 7.10.1RC2 going forward becoming part of GHC 7.10.1? It's not like
having something implemented in GHC makes it magically become written
into stone for the next Haskell Report.

We've been already preparing Hackage for this change in `base` since
even before GHC 7.10.1RC1 was released last year[1], with the implicit
assumption that the release-candidate would be very representative of
what GHC 7.10.1 is going to look like so Hackage upstream authors could
adapt their packages with confidence. When RC1 came out, Michael was so
kind to throw the Stackage-machinery at testing GHC 7.10 and informing
even more package-authors in case their packages needed attention.

Reverting BBP may cause additional work for those package authors that
adapted their packages by removing now redundant imports to achieve
perfect `-Wall`-hygiene.

So what are the tangible problems with the current BBP? Code-breakage
doesn't seem to be the issue here. To the contrary, you seem to rather
suggest to actively cause a major compatibility breakage in order to do
BBP "right" (as you consider generalising the signatures in `Data.List`
to be "wrong"[2] -- it would help if you could elaborate more concretely
what the actual problem is, so I can actually try to address that
concern).

-- hvr.

 [1]: Edward states in

      https://www.reddit.com/r/haskell/comments/2ttvsj/major_prelude_changes_proposed/co2m5su

      that 569 packages of the Stackage-set are building with GHC 7.10.1
      just fine

 [2]: https://www.reddit.com/r/haskell/comments/2ttvsj/major_prelude_changes_proposed/co3doue