[Haskell-cafe] is there a way to patch the build-depends line of a cabal file without breaking backwards compatibility?

[Thomas Schilling]

On 20 aug 2007, at 18.37, Thomas Hartman wrote:

>
> cafe, is there a way to patch the build-depends line of a cabal  
> file without breaking backwards compatibility?
>
> I just patched HDBC head to compile under ghc 6.7. Unfortunately it  
> now won't compile in 6.6.1.
>
> is there a way for build-depends to detect which version of ghc  
> you're on?
>
> also I seem to recall that -fglasgow-exts was deprecated under 6.7.  
> is there a better way to beat back the error message below than this?
>

The next release of Cabal (and the current HEAD) supports  
conditionals to test for flags, os/arch, and implementation  
(+version).  Note that the problem isn't the GHC version, but the new  
base version, in which the old base was split up into smaller  
packages, so we have something roughly like:  base-1.0 = base-2.0 +  
bytestring + old-time + mtl.  Take a look at the Cabal.cabal file,  
how this is solved, atm.  Please also note that this might not be the  
best way to use the new features;  as I suggested in another thread,  
simulating base-1.0 on systems with base-2.0 is probably best handled  
with a base.cabal file that imports base-2.0, old-time, etc. and re- 
exports all imported modules to get a "virtual" base-1.0.

/ Thomas