September 2015 - ghc-devs

RE: vectorisation code?
by Simon Peyton Jones 12 Sep '16

12 Sep '16

Austin, (or anyone else) Manuel says: | > Would it be ok if we left it in the repo, but CPP'd it out so that | we | > didn't compile everything? (The DPH library is in the same state at | > the moment.) | > | > It might suffer bit-rot, but it’d still be there for resurrection. | | Sure, that’s ok. Could you action this? Just avoid compiling anything in 'vectorise/', using (I suppose) cpp to create a stub where necessary. Leave enough comments to explain! Simon | | I hope everything is fine in Cambridge! | Manuel | | > | -----Original Message----- | > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of | > | Manuel M T Chakravarty | > | Sent: 16 January 2015 02:58 | > | To: Richard Eisenberg | > | Cc: ghc-devs(a)haskell.org Devs | > | Subject: Re: vectorisation code? | > | | > | [Sorry, sent from the wrong account at first.] | > | | > | We currently don’t have the resources to work on DPH. I would | > | obviously prefer to leave the code in, in the hope that we will be | > | able to return to it. | > | | > | Manuel | > | | > | > Richard Eisenberg <eir(a)cis.upenn.edu>: | > | > | > | > Hi devs, | > | > | > | > There's a sizable number of modules in the `vectorise` | > | subdirectory of GHC. I'm sure these do all sorts of wonderful | > | things. But what, exactly? And, does anyone make use of these | wonderful things? | > | > | > | > A quick poking through the code shows a tiny link between the | > | vectorise code and the rest of GHC -- the function `vectorise` | > | exported from the module `Vectorise`, which is named in exactly | one | > | place from SimplCore. From what I can tell, the function will be | > | called only when `-fvectorise` is specified, and then it seems to | > | interact with a {-# VECTORISE #-} pragma. However, `{-# VECTORISE | > | #-}` doesn't appear in the manual at all, and `-fvectorise` is | > | given only a cursory explanation. It seems these work with DPH... | > | which has been disabled, no? Searching online finds several hits, | > | but nothing more recent than 2012. | > | > | > | > I hope this question doesn't offend -- it seems that | > | vectorisation probably has amazing performance gains. Yet, the | > | feature also seems unloved. In the meantime, compiling (and | > | recompiling, and | > | recompiling...) the modules takes time, as does going through | them | > | to propagate changes from elsewhere. If this feature is truly | > | orphaned, unloved, and unused at the moment, is it reasonable to | > | consider putting it on furlough? | > | > | > | > Thanks, | > | > Richard | > | > _______________________________________________ | > | > ghc-devs mailing list | > | > ghc-devs(a)haskell.org | > | > http://www.haskell.org/mailman/listinfo/ghc-devs | > | | > | _______________________________________________ | > | ghc-devs mailing list | > | ghc-devs(a)haskell.org | > | http://www.haskell.org/mailman/listinfo/ghc-devs

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Unlifted data types
by Edward Z. Yang 29 Dec '15

29 Dec '15

Hello friends, After many discussions and beers at ICFP, I've written up my current best understanding of the unlifted data types proposal: https://ghc.haskell.org/trac/ghc/wiki/UnliftedDataTypes Many thanks to Richard, Iavor, Ryan, Simon, Duncan, George, Paul, Edward Kmett, and any others who I may have forgotten for crystallizing this proposal. Cheers, Edward

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arc land changes author
by Joachim Breitner 19 Dec '15

19 Dec '15

Hi, I was just about to apply a DR by David. First I ran $ arc patch D390 which put me on a feature branch. Then I reworded the commit with $ git commit --amend and then I tried to land it with $ arc land Luckily I also passed --hold... It even asked me if I want to land the commit although I am not the author: This branch has revision 'D390: Reorder GHC.List; fix performance regressions' but you are not the author. Land this revision by dfeuer? [y/N] y But it still put me in the author field: $ git show HEAD commit a387c359b99667ce55016de3816b5d9873a155db Author: Joachim Breitner <mail(a)joachim-breitner.de> Date: Wed Oct 29 08:17:05 2014 +0100 Reorder GHC.List; fix performance regressions Summary: Rearrange some oddly placed code. (and undid my commit message changes....) Did I do something wrong? Anyways, it said something along the lines of Cleaning up feature branch... (Use `git checkout -b 'arcpatch-D390' 'a3ceb0e7f44d53f728fb8bd0dfb4c97297818029'` if you want it back.) so with $ git commit --amend -C a3ceb0e7f44d53f728fb8bd0dfb4c97297818029 I was able to get the edited commit message with the right author back. Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

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A GHC Library
by Richard Eisenberg 08 Dec '15

08 Dec '15

Hi devs, It has struck me that we have a vast trove of documentation about GHC in the form of academic papers, but little organization to this trove. The papers are scattered across authors' websites, and sometimes it is hard to remember what a paper is titled when searching for it. I have thus started a wiki page here: https://ghc.haskell.org/trac/ghc/wiki/Library I would love for this page to be the Definitive List of GHC-related papers. The list I've included is, of course, woefully short, but it is a starting point. Please add to it! Have you written a GHC paper? If so, make sure it's included. Thanks, Richard

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Re: Proposal: accept pull requests on GitHub
by Thomas Miedema 20 Nov '15

20 Nov '15

> > The real hint is that "the number of contributions will go up". That's > a noble goal and I think it's at the heart of this proposal. > It's not. What's at the heart of my proposal is that `arc` sucks. Most of those quotes I posted are from regular contributors (here's another one: "arcanist kinda makes stuff even more confusing than Git by itself"). Newcomers will give it their best shot, thinking it's just another thing they need to learn, thinking it's their fault for running into problems, thinking they'll get the hang of it eventually. Except they won't, or at least I haven't, after using it for over a year. Maybe the fundamental problem with Phabricator is that it doesn't understand Git well, and the problems I posted on https://ghc.haskell.org/trac/ghc/wiki/WhyNotPhabricator are just symptoms of it. I'm having trouble putting this into words though (something about branches and submodules). Perhaps someone else can? In my opinion it's is a waste of our time trying to improve `arc` (it is 34000 lines of PHP btw + another 70000 LOC for libphutil), when `pull requests` are an obvious alternative that most of the Haskell community already uses. When you're going to require contributors to use a non-standard tool to get patches to your code review system, it better just work. `arc` is clearly failing us here, and I'm saying enough is enough. I need to think about your other points. Thank you for the thorough reply. > Here's the meat of it question: what is the cost of achieving this > goal? That is, what amount of work is sufficient to make this goal > realizable, and finally - why is GitHub *the best use of our time for > achieving this?* That's one aspect of the cost - that it's the best > use of the time. I feel like this is fundamentally why I always seem > to never 'get' this argument, and I'm sure it's very frustrating on > behalf of the people who have talked to me about it and like GitHub. > But I feel like I've never gotten a straight answer for GHC. > > If the goal is actually "make more people contribute", that's pretty > broad. I can make that very easy: give everyone who ever submits a > patch push access. This is a legitimate way to run large projects that > has worked. People will almost certainly be more willing to commit, > especially when overhead on patch submission is reduced so much. Why > not just do that instead? It's not like we even mandate code review, > although we could. You could reasonably trust CI to catch and revert > things a lot of the time for people who commit directly to master. We > all do it sometimes. > > I'm being serious about this. I can start doing that tomorrow because > the *cost is low*, both now and reasonably speaking into some > foreseeable future. It is one of many solutions to raw heart of the > proposal. GitHub is not a low cost move, but also, it is a *long term > cost* because of the technical deficiencies it won't aim to address > (merge commits are ugly, branch reviews are weak, ticket/PR namespace > overlaps with Trac, etc etc) or that we'll have to work around. > > That means that if we want GitHub to fix the "give us more > contributors" problem, and it has a high cost, it not only has _to fix > the problem_, it also has to do that well enough to offset its cost. I > don't think it's clear that is the case right now, among a lot of > other solutions. > > I don't think the root issue is "We _need_ GitHub to get more > contributors". It sounds like the complaint is more "I don't like how > Phabricator works right now". That's an important distinction, because > the latter is not only more specific, it's more actionable: > > - Things like Arcanist can be tracked as a Git submodule. There is > little to no pain in this, it's low cost, and it can always be > synchronized with Phabricator. This eliminates the "Must clone > arcanist" and "need to upgrade arcanist" points. > > - Similarly when Phabricator sometimes kills a lot of builds, it's > because I do an upgrade. That's mostly an error on my part and I can > simply schedule upgrades regularly, barring hotfixes or somesuch. That > should basically eliminate these. The other build issues are from > picking the wrong base commit from the revision, I think, which I > believe should be fixable upstream (I need to get a solid example of > one that isn't a mega ultra patch.) > > - If Harbormaster is not building dependent patches as mentioned in > WhyNotPhabricator, that is a bug, and I have not been aware of it. > Please make me aware of it so I can file bugs! I seriously don't look > at _every_ patch, I need to know this. That could have probably been > fixed ASAP otherwise. > > - We can get rid of the awkwardness of squashes etc by using > Phabricator's "immutable" history, although it introduces merge > commits. Whether this is acceptable is up to debate (I dislike merge > commits, but could live with it). > > - I do not understand point #3, about answering questions. Here's > the reality: every single one of those cases is *almost always an > error*. That's not a joke. Forgetting to commit a file, amending > changes in the working tree, and specifying a reviewer are all total > errors as it stands today. Why is this a minus? It catches a useful > class of 'interaction bugs'. If it's because sometimes Phabricator > yells about build arifacts in the tree, those should be .gitignore'd. > If it's because you have to 'git stash' sometimes, this is fairly > trivial IMO. Finally, specifying reviewers IS inconvenient, but > currently needed. We could easily assign a '#reviewers' tag that would > add default reviewers. > - In the future, Phabricator will hopefully be able to > automatically assign the right reviewers to every single incoming > patch, based on the source file paths in the tree, using the Owners > tool. Technically, we could do that today if we wanted, it's just a > little more effort to add more Herald rules. This will be far, far > more robust than anything GitHub can offer, and eliminates point #3. > > - Styling, linting etc errors being included, because reviews are > hard to create: This is tangential IMO. We need to just bite the > bullet on this and settle on some lint and coding styles, and apply > them to the tree uniformly. The reality is *nobody ever does style > changes on their own*, and they are always accompanied by a diff, and > they always have to redo the work of pulling them out, Phab or not. > Literally 99% of the time we ask for this, it happens this way. > Perhaps instead we should just eliminate this class of work by just > running linters over all of the source code at once, and being happy > with it. > > Doing this in fact has other benefits: like `arc lint` will always > _correctly_ report when linting errors are violated. And we can reject > patches that violate them, because they will always be accurate. > > - As for some of the quotes, some of them are funny, but the real > message lies in the context. :) In particular, there have been several > cases (such as the DWARF work) where the idea was "write 30 commits > and put them on Phabricator". News flash: *this is bad*, no matter > whether you're using Phabricator or not, because it makes reviewing > the whole thing immensely difficult from a reviewer perspective. The > point here is that we can clear this up by being more communicative > about what we expect of authors of large patches, and communicating > your intent ASAP so we can get patches in as fast as possible. Writing > a patch is the easiest part of the work. > > And more: > > - Clean up the documentation, it's a mess. It feels nice that > everything has clear, lucid explanations on the wiki, but the wiki is > ridiculously massive and we have a tendancy for 'link creep' where we > spread things out. The contributors docs could probably stand to be > streamlined. We would have to do this anyway, moving to GitHub or not. > > - Improve the homepage, directly linking to this aforementioned page. > > - Make it clear what we expect of contributors. I feel like a lot of > this could be explained by having a 5 minute drive-by guide for > patches, and then a longer 10-minute guide about A) How to style > things, B) How to format your patches if you're going to contribute > regularly, C) Why it is this way, and D) finally links to all the > other things you need to know. People going into Phabricator expecting > it to behave like GitHub is a problem (more a cultural problem IMO but > that's another story), and if this can't be directly fixed, the best > thing to do is make it clear why it isn't. > > Those are just some of the things OTTOMH, but this email is already > way too long. This is what I mean though: fixing most of these is > going to have *seriously smaller cost* than moving to GitHub. It does > not account for "The GitHub factor" of people contributing "just > because it's on GitHub", but again, that value has to outweigh the > other costs. I'm not seriously convinced it does. > > I know it's work to fix these things. But GitHub doesn't really > magically make a lot of our needs go away, and it's not going to > magically fix things like style or lint errors, the fact Travis-CI is > still pretty insufficient for us in the long term (and Harbormaster is > faster, on our own hardware, too), or that it will cause needlessly > higher amounts of spam through Trac and GitHub itself. I don't think > settling on it as - what seems to be - a first resort, is a really > good idea. > > > On Wed, Sep 2, 2015 at 4:09 PM, Niklas Hambüchen <mail(a)nh2.me> wrote: > > On 02/09/15 22:42, Kosyrev Serge wrote: > >> As a wild idea -- did anyone look at /Gitlab/ instead? > > > > Hi, yes. It does not currently have a sufficient review functionality > > (cannot handle multiple revisions easily). > > > > On 02/09/15 20:51, Simon Marlow wrote: > >> It might feel better > >> for the author, but discovering what changed between two branches of > >> multiple commits on github is almost impossible. > > > > I disagree with the first part of this: When the UI of the review tool > > is good, it is easy to follow. But there's no open-source implementation > > of that around. > > > > I agree that it is not easy to follow on Github. > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > > > > -- > Regards, > > Austin Seipp, Haskell Consultant > Well-Typed LLP, http://www.well-typed.com/ > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >

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Proposal: accept pull requests on GitHub
by Thomas Miedema 02 Nov '15

02 Nov '15

Hello all, my arguments against Phabricator are here: https://ghc.haskell.org/trac/ghc/wiki/WhyNotPhabricator. Some quotes from #ghc to pique your curiosity (there are some 50 more): * "is arc broken today?" * "arc is a frickin' mystery." * "i have a theory that i've managed to create a revision that phab can't handle." * "Diffs just seem to be too expensive to create ... I can't blame contributors for not wanting to do this for every atomic change" * "but seriously, we can't require this for contributing to GHC... the entry barrier is already high enough" GitHub has side-by-side diffs <https://github.com/blog/1884-introducing-split-diffs> nowadays, and Travis-CI can run `./validate --fast` comfortably <https://travis-ci.org/ghc/ghc/builds>. *Proposal: accept pull requests from contributors on https://github.com/ghc/ghc <https://github.com/ghc/ghc>.* Details: * use Travis-CI to validate pull requests. * keep using the Trac issue tracker (contributors are encouraged to put a link to their pull-request in the 'Differential Revisions' field). * keep using the Trac wiki. * in discussions on GitHub, use https://ghc.haskell.org/ticket/1234 to refer to Trac ticket 1234. The shortcut #1234 only works on Trac itself. * keep pushing to git.haskell.org, where the existing Git receive hooks can do their job keeping tabs, trailing whitespace and dangling submodule references out, notify Trac and send emails. Committers close pull-requests manually, just like they do Trac tickets. * keep running Phabricator for as long as necessary. * mention that pull requests are accepted on https://ghc.haskell.org/trac/ghc/wiki/WorkingConventions/FixingBugs. My expectation is that the majority of patches will start coming in via pull requests, the number of contributions will go up, commits will be smaller, and there will be more of them per pull request (contributors will be able to put style changes and refactorings into separate commits, without jumping through a bunch of hoops). Reviewers will get many more emails. Other arguments against GitHub are here: https://ghc.haskell.org/trac/ghc/wiki/WhyNotGitHub. I probably missed a few things, so fire away. Thanks, Thomas

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MIN_VERSION macros
by David Feuer 22 Oct '15

22 Oct '15

Cabal defines MIN_VERSION_* macros that allow CPP in a Haskell source file to get information about the versions of the packages that module is being compiled against. Unfortunately, these macros are not available when not compiling with cabal, so packages must either 1. Insist on cabal compilation. This is not very friendly to developers. 2. Make "pessimistic" assumptions, assuming that all the packages are old. This makes it annoying to test new features while also leading to compilation or run-time failures when packages have removed it changed features. 3. Attempt to guess the version based on the GHC version. This works reasonably well for base, ghc-prim, containers, etc., but not so well/at all for others. Would there be some way to get GHC itself to provide these macros to all modules that request CPP? David Feuer

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[GHC] #10913: deprecate and then remove -fwarn-hi-shadowing
by Chris Upshaw 28 Sep '15

28 Sep '15

It seems like we lost the code that -fwarn-hi-shadow switched during the add of hierarchical modules in 5.0. And while the hierarchical system makes the common way .hi files could get shadowed impossible, you can still get .hi file shadowing if you use the -i flag on multiple folders. Do we care? It is a potential source of very hard to find bugs, but it is also kind of a pathological case with how the modern module system works.

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Status of deprecation/warning features (was: Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`)
by Herbert Valerio Riedel 28 Sep '15

28 Sep '15

On 2015-09-28 at 04:56:13 +0200, David Feuer wrote: [...] > That's an excellent idea, and I think it makes sense to offer it at the > module level as well as the class level. Just change DEPRECATED to REMOVED > when it's actually removed. Speaking of such, has the deprecated export > proposal made any headway? As far as the in-flight library proposals are concerned, I plan to rather have hardwired specific warnings implemented in the style of the AMP warnings as it's crucial to have them available for the GHC 8.0 release to have the foundations for the migration plans in place. We can generalize those feature later-on (maybe even in time for GHC 8.0 if we're lucky). ---- As for the more general facilities the short answer is: They're stalled! Volunteers wanted! There's the specification over at - https://ghc.haskell.org/trac/ghc/wiki/Design/MethodDeprecations and there are 3 somewhat connected/related warning-feature tickets which ought to be co-designed to avoid obstructing each other (if there's any risk there). - https://ghc.haskell.org/trac/ghc/ticket/10071 - https://ghc.haskell.org/trac/ghc/ticket/2119 - https://ghc.haskell.org/trac/ghc/ticket/4879 For #10071 there's a very modest start at implementing this, which just modifies the parser but doesn't go much farther (see wip/T10071 branch) There's an old patch for #4879 which still works over at - https://phabricator.haskell.org/D638 Cheers, hvr

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RE: How to get types including constraints out of TypecheckedModule
by Simon Peyton Jones 25 Sep '15

25 Sep '15

| What if I have a binder: | | (foo, bar) = (show, show) | | I can now get the polymorphic types of foo and bar respectively but | how do I'm not sure how I'm meant to zip up the monomorphic type of | `pat_rhs_ty`, i.e. the type of the whole rhs, with the polymorphic | types in `abs_exports`. | | I mean I could just match up the type variables and pull the | constraints in by hand but it just seems like there already ought to | be a way to do this somewhere? I'm sorry I don't understand the question. For the above pattern binding you'll get something like AbsBinds { abe_tvs = [a,b] abe_ev_vars = [ d1 :: Show a, d2 :: Show b ] abe_exports = [ ABE { abe_poly = foo :: forall a. Show a => a->String , abe_mono = foo_m :: a->String , abe_wrap = ... } ABE { abe_poly :: bar :: forall b. Show b => b->String abe_mono = bar_m :: b->String ... } ] abe_binds = { (foo_m, bar_m) = (show a d1, show b d2) } } Simon | | Alternatively my strategy to do this would be to build a map from | TyVar to the constraint and then going over the monomorphic types and | for each TyVar that's mentioned in the monomorphic type pull in the | relevant constraint and apply those to the monomorphic type. Does that | sound sensible at all? I have no idea how equality constraints and all | that fancy stuff are encoded so I hope that doesn't need any special | handling ;) | | > I hope this is of some help. If so, would you like to update the | > Commentary (on the GHC wiki) to add the information you wish had | been | > there in the first place? Thanks! | | Very much so, thanks :) | | I'd love to put this in the commentary somewhere but looking at | https://ghc.haskell.org/trac/ghc/wiki/Commentary I can't actually find | anywhere this would fit in and it just seems like an awefully specific | thing to put there. Maybe it would be better to improve the comments | instead for the next person that goes looking thoguth the source | trying to figure out where the types end up. | | For example the comment on AbsBinds could mention that this is where | the typechecker stores inferred constrainst or something like that. | | --Daniel

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