GHC 7.8 release status

[Austin Seipp]

Just my 02c: I feel the GHC API is allowed to be less stable and a
little more in-flux than most things. We've never particularly
advertised stability here anyway, so having a design that evolves a
little is reasonable, IMO. Perhaps it being in the release will help
drive more feedback, earlier.

I think we should at least get a full code review in, of course, and
address any outstanding technical concerns (like DLL splitting.) I'll
schedule this for later this week with Edsko and Luite, if nobody has
objections.

On Mon, Sep 9, 2013 at 9:55 AM, Edsko de Vries <edskodevries at gmail.com> wrote:
> Simon,
>
> I talked to Luite this morning and I think we can come up with a
> design that includes the enumeration we prefer, with a single use of
> Dynamic in DynFlags -- it involves splitting off a PackageState module
> from Packages so that DynFlags doesn't depend on the entirely of
> Packages anymore (which would then, transitively, mean that it depends
> on Hooks and hence on a large part of ghc), but I think that should be
> doable. I'm working on that now.
>
> Edsko
>
> On Mon, Sep 9, 2013 at 3:51 PM, Simon Peyton-Jones
> <simonpj at microsoft.com> wrote:
>> Edsko
>>
>>
>>
>> I’m very short of time right now. I think you understand the issues here.
>> Can you do a round or two with Luite and emerge with a design that you both
>> think is best?
>>
>>
>>
>> As I said earlier I’m uncomfortable with doing design work so late in the
>> cycle, and I feel that I don’t have time to study the various alternatives
>> properly in the next four days.  But since you tell me it’s crucial for
>> GHCJS, I suppose that a possible compromise is this.  We release a GHC with
>> some design for hooks, but specifically say that the hook design is evolving
>> and may well change with the next version.  And then you two, with Thomas
>> and other interested parties, work together to evolve a design that everyone
>> is happy with.
>>
>>
>>
>> Does that sound ok?
>>
>>
>>
>> Simon
>>
>>
>>
>> From: Luite Stegeman [mailto:stegeman at gmail.com]
>> Sent: 07 September 2013 22:04
>> To: Simon Peyton-Jones
>> Cc: Thomas Schilling; Edsko de Vries; ghc-devs
>>
>>
>> Subject: Re: GHC 7.8 release status
>>
>>
>>
>> ·         Why aren’t you using Data.Dynamic for the hook things?  You are
>> precisely doing dynamic typing after all.  (Moreover I want to change
>> Data.Dynamic so that it says
>>
>>      data Dynamic where
>>          Dyn :: Typeable a => a -> Dynamic
>> and you want to take advantage of this.
>>
>>
>>
>> Ah the goal is to avoid the Typeable constraint on the hooked function, and
>> to identify what things are actually hooks. Wrapping it in a newtype also
>> achieves the first goal and does make the design a bit simpler.
>>
>>
>>
>> No need for these strange “data DsForeignsHook = DsForeignsHook” things, or
>> for the Hook type family.  Simple!
>>
>> But it means that hooks are no longer recognisable by their type, they're
>> just some Typeable (the type families approach would at least prevent users
>> from accidentally inserting wrong hooks, even though they would still be
>> able to make bogus instances on purpose)
>>
>> ·         The design *must* list all the hooks that GHC uses and their
>> types.  There’s no point in adding a hook that GHC doesn’t call!
>>
>> It appears to be difficult to define all hooks in one module or have them in
>> one record because of dependencies and the DLL split on Windows.
>> Re-exporting everything from a single module can be done, but would offer no
>> guarantees about completeness.
>>
>>
>>
>> With the type families design, everything that's an instance of Hook is a
>> hook, although the definitions are scattered throughout the GHC source. The
>> Dynamic design would just have to rely on a consistent naming convention.
>> Would listing the hooks in comments (in the Hooks module) and on the wiki be
>> a reasonable way to document them?
>>
>>
>>
>> I've uploaded a new patch, using Dynamic, although I'm not sure if it's an
>> improvement over the original one:
>>
>>
>>
>> - patch:
>> https://github.com/ghcjs/ghcjs-build/blob/master/refs/patches/ghc-hooks-dynamic.patch
>>
>> - updated hooksDemo: https://gist.github.com/luite/6478973
>>
>>
>>
>> It also adds hscParse' and tcRnModule' exports for Edsko's use case (I think
>> that makes it somewhat more flexible than exporting another version of
>> hscFileFrontend, since it allows users to write a hook that does something
>> between parsing and typechecking or one that overrides one of these phases)
>>
>>
>>
>> luite
>>
>>
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>
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-- 
Regards,
Austin - PGP: 4096R/0x91384671