[Haskell-cafe] Poll: Do you need to be able to build darcs from source on GHC 6.6?

Mitchell, Neil neil.mitchell.2 at credit-suisse.com
Wed Oct 29 07:17:35 EDT 2008


I believe the major darcs issue is the changed GADT implementation
between 6.6, so that neither 6.6 or 6.8 is a superset/subset of the
other - leading to a situation where they have to use a common subset of



> -----Original Message-----
> From: haskell-cafe-bounces at haskell.org 
> [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Duncan Coutts
> Sent: 29 October 2008 10:29 am
> To: dagit at codersbase.com
> Cc: darcs-users at darcs.net list; haskell-cafe
> Subject: Re: [Haskell-cafe] Poll: Do you need to be able to 
> build darcs from source on GHC 6.6?
> On Mon, 2008-10-27 at 19:24 -0700, Jason Dagit wrote:
> > Hello,
> > 
> > I would like to find out if any darcs users who build from 
> the source 
> > are still using ghc 6.6?
> I'd just like to point out (again ;-) ) than it's not that 
> hard to support older platforms. The only constraint is that 
> people not squeal at the sight of bundled code. The bundling 
> can be done in such a way that it's not a maintenance burden, 
> indeed it can remove the need to maintain internal 
> equivalents of external libs.
> For example for an external package foo, we could put the 
> latest stable version of it in lib/foo and in the .cabal file 
> say something like:
> flag external-foo
>   description: Use the external package foo, or the bundled version
>   default: True
> executable whatever
>   if flag(external-foo)
>     build-depends: foo == 1.*
>   else
>     hs-source-dirs: lib/foo
> And I think that's it for simple external packages (though 
> I've not tested). For external packages that use C files or 
> link to C code it needs a bit more to bundle, but not a lot 
> more. In either case the internal code should be able to 
> import the standard module name without using any CPP.
> The advantage of course is less cpp, a single API, and not 
> having to test two implementations (because the bundled impl 
> is the same as the external impl).
> Duncan
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