We need to add role annotations for 7.8

Johan Tibell johan.tibell at gmail.com
Thu Mar 13 20:20:07 UTC 2014

I get around to it next time I make a release of unordered-containers.
Filed https://github.com/tibbe/unordered-containers/issues/73 so I don't

On Thu, Mar 13, 2014 at 9:12 PM, Richard Eisenberg <eir at cis.upenn.edu>wrote:

> This is not shipped with GHC. Johan, as the maintainer of
> unordered-containers, would you be able to use my patch to be able to do
> this on your end?
> Thanks,
> Richard
> On Mar 13, 2014, at 2:50 PM, Edward Kmett <ekmett at gmail.com> wrote:
> That looks correct to me. Analogously for HashMap in unordered-containers
> of course.
> On Thu, Mar 13, 2014 at 2:49 PM, Johan Tibell <johan.tibell at gmail.com>wrote:
>> If you send a pull request for containers I'll merge it and make a
>> release. It needs to be backwards compatible with the last 3 major GHC
>> releases. I think we need to bump the minor version number so people can
>> reliable write dependency bounds to depend on the role being there (as that
>> might be the difference between code compiling or not).
>> Here's a guess which params should be representational:
>> Map k v -- k: nominal, v: represententional
>> Set a -- k: nominal
>> IntMap v -- v: represententional
>> Sequence a -- a: represententional
>> Tree a -- a: represententional
>> On Thu, Mar 13, 2014 at 7:41 PM, Richard Eisenberg <eir at cis.upenn.edu>wrote:
>>> Hi libraries, Johan, Edward,
>>> tl;dr: We really should add role annotations to the libraries that ship
>>> with GHC 7.8.
>>> In November, I sent this out:
>>> http://www.haskell.org/pipermail/libraries/2013-November/021707.html
>>> It got several good responses. Some time later, Joachim and I noticed
>>> that no action was taken, so we made a bug report, #8718, with a milestone
>>> of 7.8.1. I believe we both assumed that would take care of it. However,
>>> Simon PJ and I were surprised earlier this week to discover that Map and
>>> Set still do not have role annotations. Perhaps the GHC Trac isn't the
>>> right place for libraries issues, but posting here didn't quite work, so
>>> that seemed like the logical next step.
>>> In any case, now that we have the ability to prevent abuses of datatypes
>>> like Map and Set through erroneous use of GeneralizedNewtypeDeriving (and
>>> the new `coerce`), we should take advantage of this fact for 7.8. See my
>>> earlier email for a full explanation.
>>> Possibly folks' unfamiliarity with roles are in part to blame for not
>>> adding these role annotations. I am happy to help sort out what goes where.
>>> But, I need to work with someone with an intimate familiarity with the
>>> libraries themselves to help determine what the correct annotations are.
>>> For example, Map's first parameter should be nominal (its Ord instance is
>>> very relevant) but its second should be representational (there are no
>>> particular invariants related to the values of a map). Map is
>>> straightforward in this respect; other types probably aren't. Furthermore,
>>> I don't have anywhere near a complete list of what even needs attention.
>>> (It should be any type abstractly exported from a library.)
>>> Can someone help? I've included Johan as the most recent uploader of
>>> `containers` and Edward as the head of the core libraries committee.
>>> Thanks!
>>> Richard
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