- ghc-devs - Haskell.org

NondecreasingIndentation (& de-tabbing several .hs files)
by Herbert Valerio Riedel 29 May '14

29 May '14

Hello GHC devs, While I refactored the ghc code base to declare LANGUAGE pragmas locally, rather than via -X-flags on the GHC commandline, I've noticed there were a couple of places where NondecreasingIndentation grammar was used. What's the current consensus on the use of NondecreasingIndentation? Is its use still encouraged? ---- Moreover, I touched several files (over 300) while refactoring, would that qualify as "working on this module" in the sense of | While working on this module you are encouraged to remove it and detab | the module (please do the detabbing in a separate patch). or would that overreach wrt the original intent of the guideline quoted above? Cheers, hvr

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Parallelizing the Weak Pointer Lock
by Edward Kmett 29 May '14

29 May '14

How hard *would* it be to replace the global weak pointer lock with something that scales better? I'm looking at switching some of my older BDD code into Haskell. To do so I'd love to be able to use an "intuitive" weak-pointer based cache management scheme, but I have to confess the notion of a global lock getting in the way basically damns whatever solution I come up with to be a single-threaded toy. =/ If I'm trying to sell Haskell's parallelism to others, it seems my only winning moves right now are: 1.) play less satisfying games with typed regions, which scale less well than the tried and tested solutions of GCing hash-consed BDD structures. 2.) just tackle the problem that allocating a weak pointer grabs a global lock. 3.) not to play the game -Edward

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Ghc 7.8 branch broken
by Simon Peyton Jones 27 May '14

27 May '14

Austin, the ghc-7.8 branch does not build. See below. Simon inplace/bin/mkUserGuidePart docs/users_guide/users_guide.xml inplace/bin/mkUserGuidePart docs/users_guide/what_glasgow_exts_does.gen.xml "rm" -rf docs/users_guide/users_guide/ "/usr/bin/xsltproc" --stringparam base.dir docs/users_guide/users_guide/ --stringparam use.id.as.filename 1 --stringparam html.stylesheet fptools.css --nonet --stringparam toc.section.depth 3 --stringparam section.autolabel 1 --stringparam section.label.includes.component.label 1 http://docbook.sourceforge.net/release/xsl/current/html/chunk.xsl docs/users_guide/users_guide.xml docs/users_guide/intro.xml:312: parser error : Entity 'relnotes3' not defined &relnotes3; ^ docs/users_guide/intro.xml:321: parser error : chunk is not well balanced ^ docs/users_guide/ug-book.xml:11: parser error : Failure to process entity intro &intro; ^ docs/users_guide/ug-book.xml:11: parser error : Entity 'intro' not defined &intro; ^ docs/users_guide/users_guide.xml:10: parser error : Failure to process entity ug-book &ug-book; ^ docs/users_guide/users_guide.xml:10: parser error : Entity 'ug-book' not defined &ug-book; ^ unable to parse docs/users_guide/users_guide.xml "cp" -p ghc/stage2/build/tmp/ghc-stage2 inplace/lib/bin/ghc-stage2 make[1]: *** [docs/users_guide/users_guide/index.html] Error 6 make[1]: *** Waiting for unfinished jobs.... make: *** [all] Error 2 simonpj@cam-05-unx:~/5builds/ghc-7.8-branch$

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Re: GHC 7.8.3 release
by Johan Tibell 27 May '14

27 May '14

I would say "sooner". Here are still unmerged things that I think we could merge before (i.e. easy to merge): https://ghc.haskell.org/trac/ghc/ticket/9001 https://ghc.haskell.org/trac/ghc/ticket/9078 https://ghc.haskell.org/trac/ghc/ticket/8475 https://ghc.haskell.org/trac/ghc/ticket/8783 https://ghc.haskell.org/trac/ghc/ticket/9068

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Weak reference semantics - why does a dead weak ref keep its value alive?
by Luite Stegeman 27 May '14

27 May '14

Hi all, I'm reviewing and improving my weak references implementation for GHCJS, among other things to make sure that the profiling/stack trace support, currently being implemented by Ömer Sinan Ağacan as a GSoC project has the correct heap information to work with. JavaScript does not have weak references with 'observable deadness', so we have to walk the heap data structures from time to time to test reachability, schedule finalizers and break the weak links. I'm trying to find a design that keeps GHC's semantics, but where JavaScript's own garbage collector can get rid of as much data as possible, even before we run our own heap scan. Now I ran into the following peculiarity, from the semantics (System.Mem.Weak documentation): A heap object is reachable if: - It is a member of the root set. - It is directly pointed to by a reachable object, other than a weak pointer object. - It is a weak pointer object whose key is reachable. - It is the value or finalizer of a weak pointer object whose key is reachable. This says that even if nothing has a reference to a weak pointer, as long as there are references to its key, the value is considered to be reachable. For example in this program import Data.Maybe import System.Mem.Weak import System.Mem import Control.Exception import System.IO import Control.Concurrent gc = performGC >> threadDelay 1000000 main = do hSetBuffering stdout NoBuffering k <- evaluate "k" v <- evaluate "v" addFinalizer v (putStrLn "fv") w <- evaluate =<< mkWeak k v (Just $ putStrLn "fkv") putStrLn =<< fmap (fromMaybe ".") (deRefWeak w) addFinalizer w (putStrLn "fw") gc putStrLn k gc there is no way to reach 'v' after `w` has been finalized, but still it's kept alive. This agrees with the semantics in the documentation, but what's the reason for this? luite

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Constructing coercions for associated type?
by Conal Elliott 25 May '14

25 May '14

I'm working on a GHC plugin in which I need to programmatically construct a coercion for an associated type, given the type function name and the type argument. For instance, I have the following class: > class Encodable a where > type Encode a > encode :: a -> Encode a > decode :: Encode a -> a along with a type instance, say `Int -> Bool`. In a GHC plugin, how can I apply a type function to an argument type to get back the resulting type and the associated coercion? (Given the latter, I think the former comes from `coercionKind`). -- Conal

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Haddock repo doesn't accept pushes?
by Dr. ERDI Gergo 25 May '14

25 May '14

Hi, I've just tried pushing a commit to the Haddock repo on git.haskell.org: 14:45:36 [cactus@galaxy haddock]$ git push -u origin HEAD Counting objects: 9, done. Delta compression using up to 4 threads. Compressing objects: 100% (5/5), done. Writing objects: 100% (5/5), 462 bytes | 0 bytes/s, done. Total 5 (delta 4), reused 0 (delta 0) remote: W refs/heads/master haddock gergo DENIED by refs/.* remote: error: hook declined to update refs/heads/master To ssh://git@git.haskell.org/haddock.git ! [remote rejected] HEAD -> master (hook declined) error: failed to push some refs to 'ssh://git@git.haskell.org/haddock.git' So, OK, maybe I don't remember correctly and I can't push to master, let's push to my branch so that I can ask someone to move it over: 14:46:47 [cactus@galaxy haddock]$ git push --force -u origin HEAD:wip/pattern-synonyms Counting objects: 9, done. Delta compression using up to 4 threads. Compressing objects: 100% (5/5), done. Writing objects: 100% (5/5), 462 bytes | 0 bytes/s, done. Total 5 (delta 4), reused 0 (delta 0) remote: + refs/heads/wip/pattern-synonyms haddock gergo DENIED by refs/.* remote: error: hook declined to update refs/heads/wip/pattern-synonyms To ssh://git@git.haskell.org/haddock.git ! [remote rejected] HEAD -> wip/pattern-synonyms (hook declined) error: failed to push some refs to 'ssh://git@git.haskell.org/haddock.git' I could try merging origin/master into the existing wip/pattern-synonyms branch but there wouldn't be much point in resolving all the merge conflicts, since my local branch (which is just one commit on top of origin/master) is already exactly what I'd want to push to master. So how do I get my commit (which is needed for a patch to GHC proper) into the Haddock repo? Thanks, Gergo

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Re: [GHC] #4213: LLVM: Add support for TNTC to LLVM compiler suite
by David Terei 23 May '14

23 May '14

Firstly, its cool that LLVM has added this. It seems we could indeed implement TNTC with it. However based my quick understanding we couldnt implement it in a wag compatible with the current design. I believe the LLVM feature only allows us to place data at the very start of the function, after the label not before it. And your meant to ensure the very first instruction of the function is a jump that jumps over the data. We could use this, Simon Marlow and I discussed such a design in the past. But it's a change from the current scheme so the NCG would also need to change and it isn't clear if it would be as good as our current design. The other issue is that fixing TNTC doesn't eliminate the mangler. We use it for a few different reasons now. I can think of at least 3 I believe: TNTC, SIMD, and Windows. As for moving to the LLVM api. No, I think that isn't a great idea. I'm not convinced its will gain much compilation speed improvement. This is testable vy measuring how much time is actually spent invoking the LLVM binaries and how much time they spend serializing and parsing files. Given we need to go to an intermediary file of assembly for the mangler... Using the API also creates a GHC build time dependency on LLVM. Right now we avoid that which has advantages. On 22/05/2014 10:12 pm, "GHC" <ghc-devs(a)haskell.org> wrote: > > #4213: LLVM: Add support for TNTC to LLVM compiler suite > -------------------------------------+------------------------------------ > Reporter: dterei | Owner: dterei > Type: feature request | Status: new > Priority: low | Milestone: 7.6.2 > Component: Compiler (LLVM) | Version: 6.13 > Resolution: | Keywords: > Operating System: Unknown/Multiple | Architecture: Unknown/Multiple > Type of failure: None/Unknown | Difficulty: Unknown > Test Case: | Blocked By: > Blocking: | Related Tickets: > -------------------------------------+------------------------------------ > > Comment (by awson): > > I'm extremely sorry for a kind of OT. There is another LLVM/infotable > related ticket, which I don't know how to solve > [https://ghc.haskell.org/trac/ghc/ticket/8974 without the mangler]. Could > you, please, look into it and check if we can fix that without mangler or, > perhaps, understand what a feature we could ask LLVM people to introduce. > > -- > Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4213#comment:14> > GHC <http://www.haskell.org/ghc/> > The Glasgow Haskell Compiler

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Call for Contributions: Haskell Implementors' Workshop 2014
by Jost Berthold 21 May '14

21 May '14

Call for Contributions ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2014 Gothenburg, Sweden, 06 September, 2014 Co-located with ICFP 2014 http://www.icfpconference.org/icfp2014/ Important dates --------------- Proposal Deadline: Monday, 14 July, 2014 (midnight, anywhere on earth) Notification: 21 July 2014 Workshop: Saturday, 6 September 2014 The 6th Haskell Implementors' Workshop is to be held alongside ICFP 2014 this year in Gothenburg. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure, to share their work and discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings; the workshop will be informal and interactive, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Attendance figures clearly reflect the growth of the Haskell user community and a constant interest in implementation aspects. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2014. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop, we hope to study the underlying technology. We want to bring together anyone interested in the nitty-gritty details behind turning plain-text source code into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for talks and demonstrations. We are aiming for 20 minute talks with 10 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words. Submissions should be made via EasyChair. The website is: https://www.easychair.org/conferences/?conf=hiw2014 If you don't have an account you can create one here: https://www.easychair.org/account/signup.cgi Because the submission is an abstract only, please click the "abstract only" button when you make your submission. There is no need to attach a separate file. We will also have a lightning talks session which will be organised on the day. These talks will be 5-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers ---------- * Jost Berthold (co-chair) (University of Copenhagen) * Kevin Hammond (University of St.Andrews) * Gabriele Keller (University of New South Wales) * Paul Liu (Intel Labs) * Rita Loogen (Philipps-Universitat Marburg) * Geoffrey Mainland (co-chair) (Drexel University, Philadelphia) * Carter Schonwald (WellPosed Ltd) Contact ------- * hiw2014(a)easychair.org * Jost Berthold <berthold at di.ku.dk> * Geoffrey Mainland <mainland at cs.drexel.edu>

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Questions about "time and space profiling for non-strict langs" paper and cost centre impl. of GHC
by Ömer Sinan Ağacan 21 May '14

21 May '14

Hi all, I'm trying to understand the paper "Time and space profiling for non-strict, higher-order functional languages"[1] and I'm hoping that experienced GHC devs here could help me clarifying some points. Here's my question: In Figure 5, I don't understand why no costs are attributed to `app2` rule(substitution rule). It looks like to me that this is the function application rule so `A` cost should be attributed here, but in the paper `A` cost is attributed in `app1` rule, which if I understand correctly shows how function part of an application is evaluated. I know about the "lexical scoping rule" explained in 2.4 and the cost should be attributed to the cost center in the scope of lambda definition instead of the cost center in "application site", but Figure 5 still doesn't make sense to me. To me it looks like that there should be two costs attributed in application rules. First cost is "evaluation of the function" part(which should be attributed in `app1` rule) and second is "substitution" part, which should be attributed in `app2` rule but according to the paper we only have the former cost, and the latter is free(e.g. no costs are attributed in second rule). It would be appreciated if someone could help me clarifying this. I'm also looking for more recent papers about GHC's profiler implementation. I'm especially interested profiling in multi-threaded RTS. Lastly, it'd be appreciated if someone could explain me two Bool fields in `StgSCC` constructor of STG syntax. Thanks! UPDATE: I was reading the paper one more time before sending my question and I found one more confusing part. In 4.1 it says "Lexical scoping will subsume all the costs of applying `and1` to its call sites..." but in 2.4 it says "Lexical scoping: Attribute the cost to "fun", the cost centre which lexically encloses the abstraction." so this two definitions of same thing is actually different. To me it looks like the definition in 4.1 is wrong,, it should be "definition site", not "call site". What am I missing here? [1]: http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=36FE097056F4E03CCD… --- Ömer Sinan Ağacan http://osa1.net

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