haddock 2 and GHC

[Simon Marlow]

Claus Reinke wrote:

> Instead of working around them in each individual case, I'd really like 
> to see general solutions to the two issues of
> 
> 1 updating ghc-paths and notifying existing clients
> 2 making (some) ghc api clients less dependent on a single ghc    version
> 
> Most suggestions about this have been shot down in the past, iirc,
> the closest to being possible were dynamic linking for 1 and some
> cross-ghc-version reading of .hi-files for 2 (at the risk of losing 
> information, because the .hi-format itself would still change; so this 
> would work only for some ghc api clients, and only for a limited range 
> of ghc versions, but haddock ought to be among those clients).

dynamic linking will solve (1), but at this stage I don't think we have 
time to get dynamic linking fully working and in the binary distributions 
for 6.10.1.  We might have it working in a build-from-source form, though.

As I've said before regarding (2), it's feasible to make the .hi format 
stable across minor releases of GHC, but not major releases.  Making an 
extensible .hi format seems completely unrealistic - it's not just the 
format that changes, but the semantics.  "Losing inforamtion" might be 
completely disastrous if you actually *needed* that information.  Not to 
mention the fact that trying to do both forwards and backwards 
compatibility in anything but a trivial way gives you a quadratic-sized 
testing surface, which is something we really have to worry about.

Cheers,
	Simon