GHC 7.8 release?

Simon Marlow marlowsd at
Sun Feb 10 21:21:41 CET 2013

On 10/02/13 15:36, Simon Peyton-Jones wrote:
> We seem to be circling ever closer to consensus here! Yay!
> Indeed!  Good :-)
> However, I’m not getting the bit about API changing vs non-API changing.
> Firstly I don’t know which APIs are intended.  The GHC API is
> essentially GHC itself, so it changes daily.  Maybe you mean the base
> package?  Or what?
> I suspect you mean that a “non-API-changing” release absolutely
> guarantees to compile any package that compiled with the previous
> version.  If so, that is a very strong constraint indeed. We do observe
> it for patch releases for GHC (e g 7.6.2 should compile anything that
> 7.6.1 compiles).  But I think it would be difficult to guarantee for
> anything beyond a patch release.  Every single commit (and the commit
> rate is many/day) would have to be evaluated against this criterion.
> And if it failed the criterion, it would have to go on a API-breaking
> HEAD. In effect we’d have two HEADs.  I can’t see us sustaining this.
> And I don’t yet really see why it’s necessary.  If you don’t want an
> API-breaking change, stick with the patch releases.
> So, we have a channel for non-API-breaking changes already: the patch
> releases.  So that means we already have all three channels!

Mark is asking for major GHC releases every year at the most, preferably 
less frequently.  That means major GHC releases in the sense that we do 
them now, where libraries change, and a wave of package updates are 
required to get everything working.

Johan, Manuel and Carter are saying that they want releases that add 
features but don't break code, i.e. a non-API-breaking release, as a way 
to get the new bits into the hands of the punters sooner.  This is 
something that we don't do right now, and it would entail a change to 
our workflow and release schedule.

It doesn't mean no API changes at all - we would have to allow APIs to 
be extended, because many feature additions come with new primops, or 
new supporting code in the ghc-prim or base packages.  The package 
version policy states precisely what it means to extend an API 
( and most 
third-party packages will still work so long as we only bump the minor 
versions of the packages that come with GHC.

The GHC package itself would have to be exempt, because it contains 
every module in GHC, and hence would be impossible to keep stable if we 
are modifying the compiler to add new features.

Of course it's not practical to maintain an extra branch of GHC for 
non-API-breaking development - two branches is already plenty.  So there 
would need to be an API-freeze for a while between the major release and 
the non-API-breaking release, during which time people developing API 
changes would need to work on branches.

Is it workable?  I'm not sure, but I think it's worth a try.  I wouldn't 
want to see this replace the patchlevel bugfix releases that we already 
do, and as Ian points out, there isn't a lot of room in the release 
schedule for more releases, unless we stretch out the timescales, doing 
major releases less frequently.


> ·Haskell Platform
> ·Patch-level releases
> ·New releases
> if that’s so, all we need is better signposting.   And I’m all for that!
> Have I got this right?
> Simon
> *From:*Mark Lentczner [mailto:mark.lentczner at]
> *Sent:* 09 February 2013 17:48
> *To:* Simon Marlow; Manuel M T Chakravarty; Johan Tibell; Simon
> Peyton-Jones; Mark Lentczner; andreas.voellmy at; Carter
> Schonwald; kostirya at; Edsko de Vries; ghc-devs at;
> glasgow-haskell-users
> *Subject:* Re: GHC 7.8 release?
> We seem to be circling ever closer to consensus here! Yay!
> I think the distinction of non-API breaking and API breaking release is
> very important. Refining SPJ's trifecta:
>     *Haskell Platform* comes out twice a year. It is based on very
>     stable version of GHC, and intention is that people can just assume
>     things on Hackage work with it. These are named for the year and
>     sequence of the release: 2013.2, 2013.2.1, 2013.4,...
>     *Non-API breaking releases* can come out as often as desired.
>     However, the version that is current as of mid-Feb. and mid-Aug.
>     will be the ones considered for HP inclusion. By non-API breaking we
>     mean the whole API surface including all the libraries bundled with
>     GHC, as well as the operation of ghc, cabal, ghc-pkg, etc. Additions
>     of features that must be explicitly enabled are okay. Additions of
>     new APIs into existing modules are discouraged: Much code often
>     imports base modules wholesale, and name clashes could easily
>     result. These should never bump the major revision number: 7.4.1,
>     7.4.2...
>     *API breaking releases* happen by being released into a separate
>     channel when ready for library owners to look at them. This channel
>     should probably go through several stages: Ready for core package
>     owners to work with, then HP package owners, then all package
>     owners. I'd imagine this is a several month process. At the end of
>     which, the release can go into the main channel. Such a merge
>     shouldn't happen more than once a year... I think even once every
>     two years is fine (!) To avoid confusion, I'd suggest that while in
>     the separate channel, these release be named with odd number: 7.9,
>     7.11,..., and when moved to the main channel renamed to even: 7.10,
>     7.12...
> This idea of three channels needs to be much more clearly communicated.
> The warning on the download page is a failure: Googling "ghc" takes you
> to the home page of GHC which immediately trumpets the "Lastest News" of
> a release of GHC 7.6.2. Once a user has read that and decided to
> download, then "STOP!" box is a) going to be skipped as they scan for
> the download link, and b) if read and followed, causes the "WTF? Why is
> HP so back rev?" So we need to change the front page so that the three
> channels are clearly communicated and targeted at the right users.
> - Mark
> (BTW: The first few links on the GHC web site are out of date: The
> second nav link is to a survey that is 7 years old. The License page is
> 8 years out of date. The FAQ is over a year old.)
> On Sat, Feb 9, 2013 at 8:24 AM, Ian Lynagh <ian at
> <mailto:ian at>> wrote:
> On Sat, Feb 09, 2013 at 12:06:12PM +0000, Simon Marlow wrote:
>  >
>  > As a straw man, let's suppose we want to do annual API releases in
>  > September, with intermediate non-API releases in February.
> That's a non-API release 5 months after the API release.
> 6.10.2 was 5   months after 6.10.1 (.3 was 1 month later, .4 a further 2)
> 6.12.2 was 4   months after 6.12.1 (.3 was 2 months later)
>   7.0.2 was 3.5 months after  7.0.1 (.3 was 1 month later, .4 a further 3)
>   7.2.2 was 3   months after  7.2.1
>   7.4.2 was 4   months after  7.4.1
>   7.6.2 was 4.5 months after  7.6.2
> so if we do non-API releases, then perhaps it would make sense to stop
> doing minor releases (unless a release turns out to just be broken).
> Thanks
> Ian

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