On 11/6/10 6:20 AM, Reiner Pope wrote:
I was aware of this condition, but I'm not precisely sure it addresses my requirements. When you run "cabal install some-package", cabal reads all version constraints listed in the "build-depends" field, and chooses which versions of which packages to download from Hackage in order to satisfy these constraints.
I want to expose my dependency on a particular version of ghc to cabal's constraint satisfier. The end result I want is that when you type "cabal install hmatrix-static" with ghc-6.12 installed, then cabal chooses hmatrix-static-0.3; and when you type "cabal install hmatrix-static" with ghc-7.0 installed, then cabal chooses hmatrix-static-0.4.
Clients of hmatrix-static would have to say if impl(ghc >= 7.0) Build-Depends: hmatrix-static == 0.4.* else Build-Depends: hmatrix-static == 0.3.* in order to pull in the right dependency for themselves. In order to get the behavior you're after, though, is trickier business. Since every version of GHC ships with a different version of base, you'll have to make use of that knowledge such that users of ghc-7.0 with base-5 will get hmatrix-static-0.4 whereas users of ghc-6.12 with base-4 will get hmatrix-static-0.3 -- Live well, ~wren