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

[Antoine Latter]

On Sat, Nov 27, 2010 at 8:38 PM, Jinjing Wang <nfjinjing at gmail.com> wrote:
> 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
>    else
>        build-depends:   base                      >= 4        && < 4.3
>
>   in library field in cabal
>
> * add `{-# LANGUAGE CPP #-}` in source file
> * add
>
>    #if GHC7
>    x
>
>    #else
>    y
>
>    #endif
>
>
>  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
>

Something like:

myQuoter = QuasiQuoter {
  quoteExp = expQuoter,
  quotePat = patQuoter
  }

Will work in either version, but it will leave the un-set fields set
to `undefined`, so you'll get a compile error if you try to use them.

I haven't tested this, but I've done it with other record types.

Take care,
Antoine