RFC: provide patch-level information at __GLASGOW_HASKELL__

[Edward Kmett]

+1 on the PATCHLEVEL variant. (for that matter, +1 on the other if it is
all I can get!)

I've wanted something like this for a long time.

-Edward


On Thu, Apr 10, 2014 at 9:57 AM, Austin Seipp <austin at well-typed.com> wrote:

> I agree with Roman. I think just adding a new PATCHLEVEL macro is the
> way to go and complementary to the existing setup, without confusing
> things.
>
> On Thu, Apr 10, 2014 at 6:18 AM, Roman Cheplyaka <roma at ro-che.info> wrote:
> > I've never needed this so far, but if this gets implemented, I'm in
> favour of
> > a separate __GLASGOW_HASKELL_PATCHLEVEL__ macro.
> >
> > As you say, the existing scheme is somewhat non-intuitive. But having two
> > schemes simultaneously carries an even bigger mental overhead.
> > And it's too easy to forget that the scheme has changed when testing for
> newer
> > ghc versions.
> >
> > Roman
> >
> > * Herbert Valerio Riedel <hvr at gnu.org> [2014-04-10 10:55:47+0200]
> >> 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.
> >>
> >> 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
> >> _______________________________________________
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> >> ghc-devs at haskell.org
> >> http://www.haskell.org/mailman/listinfo/ghc-devs
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> >
>
>
>
> --
> Regards,
>
> Austin Seipp, Haskell Consultant
> Well-Typed LLP, http://www.well-typed.com/
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