Hi, I'm bringing up an old thread, because it's very relevant to my problem. On Tue, Nov 18, 2008 at 22:30, Duncan Coutts wrote:
On Tue, 2008-11-18 at 01:48 -0800, Jason Dusek wrote:
I'd like to be able to do something like:
if (template-haskell < 2.3) cpp-options: -D TH_THE_YOUNGER else cpp-options: -D TH_THE_ELDER
I guess this kind of thing is not possible at present?
It is possible, in two different ways.
The easiest way is that if you're using Cabal-1.6 then it provides cpp macros to test the version number of packages you're using.
#if MIN_VERSION_template_haskell(2,3,0) ... #elseif ... #endif
The alternative that works back to Cabal-1.2 is to use:
flag newer-th
... if flag(newer-th) build-depends: template-haskell >= 2.3 cpp-options: -D TH_THE_ELDER else build-depends: template-haskell < 2.3 cpp-options: -D TH_THE_YOUNGER
Either I'm doing something wrong or this doesn't work for cabal-install and GHC 6.8.3. I used the "flag newer-th" approach in EMGM: https://svn.cs.uu.nl:12443/viewvc/dgp-haskell/EMGM/tags/emgm-0.2/emgm.cabal?... [...] flag th23 description: Define a CPP flag that enables conditional compilation for template-haskell package version 2.3 and newer. Library [...] build-depends: base >= 3.0 && < 4.0, template-haskell < 2.4 -- Include deriveRep for Loc. This was introduced with -- template-haskell-2.3, included with GHC 6.10. if flag(th23) build-depends: template-haskell >= 2.3 cpp-options: -DTH_LOC_DERIVEREP else build-depends: template-haskell < 2.3 [...] When I run cabal install emgm (with GHC 6.8.3 and either Cabal 1.2 or 1.6), it tries (and fails) to install template-haskell-2.3. That's exactly what I don't want. Any suggestions? Thanks, Sean