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

Jinjing Wang nfjinjing at gmail.com
Sun Nov 28 03:38:15 CET 2010

Hi Michael, you are absolutely correct, cabal did set the flags automatically.

To sum up, here's what needs to be done:

* add `flag ghc7` as a field in cabal
* add:

    if flag(ghc7)
        build-depends:   base                      >= 4.3      && < 5
        cpp-options:     -DGHC7
        build-depends:   base                      >= 4        && < 4.3

   in library field in cabal

* add `{-# LANGUAGE CPP #-}` in source file
* add

    #if GHC7



 Hi Antonine, I don't know how to not set those fields in the
constructor.. as a QQ noob, I'm just hacking on some legacy code. This
code doesn't compile in GHC7, so I have to do this trick.

* https://github.com/nfjinjing/mps/blob/master/src/MPS/TH.hs


On Sun, Nov 28, 2010 at 3:48 AM, Michael Snoyman <michael at snoyman.com> wrote:
> On Sat, Nov 27, 2010 at 9:41 PM, Antoine Latter <aslatter at gmail.com> wrote:
>> On Sat, Nov 27, 2010 at 10:59 AM, 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
>> Can you just not set those fields? Then the code should work as-is for
>> both versions. You'll get warnings for GHC 7, I think.
> Sorry Jinjing, I didn't read your original email carefully enough.
> Antoine is absolutely correct, this is the better way to deal with
> defining a quasiquoter. My suggestion is only necessary if you want to
> *use* a quasiquoter.
> Michael


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