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

27 Nov 2010

      Hi Antoine, Thanks for pointing out, it did work.

By using a record style constructor, the code can be made to support
both version, something like

    here = QuasiQuoter
      {
        quoteExp = (litE . stringL)
      , quotePat = (litP . stringL)
      }

in GHC7 there's a warning:

       Warning: Fields of `QuasiQuoter' not initialised: quoteType, quoteDec

So far it works without problem.

On Sun, Nov 28, 2010 at 10:38 AM, Jinjing Wang  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
Best,
On Sun, Nov 28, 2010 at 3:48 AM, Michael Snoyman  wrote:
...
On Sat, Nov 27, 2010 at 9:41 PM, Antoine Latter  wrote:
...
On Sat, Nov 27, 2010 at 10:59 AM, Jinjing Wang  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.htm...
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
--
jinjing
-- 
jinjing