[Haskell-cafe] Conditional compilation for different versions of GHC?

[Jinjing Wang]

Thanks Michael,

So the user should use `cabal install --flags -ghc7 package-name` to
install the package, if I'm not mistaken?

Will it work if the package is installed as a dependency? Will the
flag environment be passed down from the root package?

Is there a way to detect GHC version automatically?

: )

Best,


On Sun, Nov 28, 2010 at 1:32 AM, Michael Snoyman <michael at snoyman.com> wrote:
> On Sat, Nov 27, 2010 at 6:59 PM, Jinjing Wang <nfjinjing at gmail.com> wrote:
>> Dear list,
>>
>> >From ghc 7.0.1 release notes:
>>
>>> The Language.Haskell.TH.Quote.QuasiQuoter type has two new fields: quoteType and quoteDec.
>>
>> Some of my code needs to be conditionally compiled to support both
>> version 6 and 7, what is the recommended way to do it?
>>
>> ref:
>>
>> * http://new-www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.html
>
> Hi Jinjing,
>
> I've done this in Yesod. I'm not sure if it's the best way, but
> basically I've added a ghc7 flag to the cabal file, and a block for
> the library that reads:
>
>    if flag(ghc7)
>        build-depends:   base                      >= 4.3      && < 5
>        cpp-options:     -DGHC7
>    else
>        build-depends:   base                      >= 4        && < 4.3
>
> Then whenever I want to quasi-quote in the code, I write:
>
> #if GHC7
>    [quasiquoter|
> #else
>    [$quasiquoter|
> #endif
>
> Michael
>



-- 
jinjing