On 10/04/2014 09:55, Herbert Valerio Riedel wrote:
Hello,
I know this has come up various times. So this is mostly an attempt to see what the current position is on this topic:
The current scheme is documented as
,---- | The value of __GLASGOW_HASKELL__ for a major release x.y.z is the | integer xyy (if y is a single digit, then a leading zero is added, so | for example in version 6.8.2 of GHC we would have | __GLASGOW_HASKELL__==608). `----
This has lead to confusion in the past, e.g. the following two values
__GLASGOW_HASKELL__ == 702
__GLASGOW_HASKELL__ == 704
were sometimes confused (by me at least) to mean 7.0.2 and 7.0.4 respectively. And sometimes when writing conditionals, it also happened that '__GLASGOW_HASKELL__ >= 722' was written to mean >= 7.2.2.
Moreover, when GHC 7.2.2 came out, it would have been useful to be able to discriminate 7.2.1 vs 7.2.2 easily, as some SafeHaskell properties changed between 7.2.1 and 7.2.2.
We omitted the patchlevel deliberately, because patchlevel releases of GHC are not supposed to change any APIs, so there should be no reason why you would want to distinguish them in the source code. If we changed something in SafeHaskell in a patchlevel release, then that was probably a mistake. We could add a __GLASGOW_HASKELL_PATCHLEVEL__ macro, but I'd like to understand more about why people need this, and whether we should be more careful about what we do in patchlevel releases. Cheers, Simon
Therefore, I'd propose to extend this constant by a patch-level digit for future GHC versions (starting with 7.10.1), i.e.
__GLASGOW_HASKELL__ == 7090 -- 7.9 branch
__GLASGOW_HASKELL__ == 7100 -- 7.10.1 release candidates __GLASGOW_HASKELL__ == 7101 -- 7.10.1 __GLASGOW_HASKELL__ == 7102 -- 7.10.2
__GLASGOW_HASKELL__ == 7121 -- 7.12.2
NB: this ensures that __GLASGOW_HASKELL__ retains its ordering relation. There's just a steeper jump from 7.8.1 to 7.10.1, but existing code using conditionals such as
#if (__GLASGOW_HASKELL__ >= 708) && (__GLASGOW_HASKELL__ < 709)
for currently existing GHC versions will continue to work as expected.
Alternative ideas:
- Define a __GLASGOW_HASKELL_PATCHLEVEL__ containing only the patch-level number.
(c.f. GNU GCC's __GNUC_PATCHLEVEL__ constant)
This one might have the least impact, as its existence can be ignored safely, and we could even use this starting with GHC 7.8.2 with low risk of affecting users.
- define a __MIN_VERSION_GHC__(x,y,z) macro in the style of Cabal's MIN_VERSION_<pkgname>() macros
While this has the most structure, this has also the issue of backward compatibility, as for earlier GHC versions you'd have to check for the existence of the macro before using it to avoid compile-time errors.
Cheers, hvr _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs