May 2014 - ghc-devs - Haskell.org

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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classP recently deleted from TH.Lib
by Gabor Greif 19 May '14

19 May '14

The last two commits from (Apr 9) on <https://github.com/ghc/packages-template-haskell/commits/master/Language/Ha…> removed a helper to construct applied type class constraints (`classP`). Some packages (notably `llvm-general-pure`) though, depend on it. Can we add back something like this: {{{ classP :: Name -> [Q Type] -> Q Pred classP cla tys = do tysl <- sequence tys return (foldl' AppT (ConT cla) tysl) }}} and export it again? Or is there such a helper with a different name already? Cheers, Gabor

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Non-exhaustive pattern-match warning in code-example from "Dependently Typed Programming with Singletons"
by Herbert Valerio Riedel 19 May '14

19 May '14

Hello *, I've been experimenting with the code from the "Dependently Typed Programming with Singletons" paper[1] from the following is derived (modulo some irrelevant renamings): {-# LANGUAGE TypeOperators, DataKinds, GADTs, TypeFamilies #-} module CheckedList where data Nat = Z | S Nat data SNat n where SZ :: SNat Z SS :: SNat n -> SNat (S n) infixr 5 :- data List l t where Nil :: List Z t (:-) :: t -> List l t -> List (S l) t type family n1 :< n2 where m :< Z = False Z :< (S m) = True (S n) :< (S m) = n :< m index :: (i :< l) ~ True => List l t -> SNat i -> t index (x :- _) SZ = x index (_ :- xs) (SS i) = index xs i The problem, though, is that with the code above GHC 7.8.2 emits a warning for the `index` function: ,---- | Pattern match(es) are non-exhaustive | In an equation for ‘index’: Patterns not matched: Nil _ `---- So I would have expected to workaround that by explicitly wrapping the length-phantom with the promoted `S` type-constructor, like so index :: (i :< S l) ~ True => List (S l) t -> SNat i -> t index (x :- _) SZ = x index (_ :- xs) (SS i) = index xs i While this would probably have silenced the pattern-match warning, I now get a type-checking error I can't seem to get rid of: ,---- | Could not deduce (l1 ~ 'S l0) from the context ((i :< 'S l) ~ 'True) | bound by the type signature for | index :: (i :< 'S l) ~ 'True => List ('S l) t -> SNat i -> t | | or from ('S l ~ 'S l1) | bound by a pattern with constructor | :- :: forall t (l :: Nat). t -> List l t -> List ('S l) t, | in an equation for ‘index’ | | or from (i ~ 'S n) | bound by a pattern with constructor | SS :: forall (n :: Nat). SNat n -> SNat ('S n), | in an equation for ‘index’ | | ‘l1’ is a rigid type variable bound by | a pattern with constructor | :- :: forall t (l :: Nat). t -> List l t -> List ('S l) t, | in an equation for ‘index’ | | Expected type: List ('S l0) t | Actual type: List l1 t | Relevant bindings include | xs :: List l1 t | | In the first argument of ‘index’, namely ‘xs’ | In the expression: index xs i `---- Is there a way to tweak the code so that GHC doesn't think there's a non-exhaustive pattern-match? Cheers, HVR [1]: http://www.cis.upenn.edu/~eir/papers/2012/singletons/paper.pdf

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RE: [commit: ghc] master: Extract derived constants from nm output for various OSes differently. (3df1c51)
by Simon Peyton Jones 19 May '14

19 May '14

Christian (and all ghc-devs) Thank you working so hard on this. I really appreciate it. But can I beg you to add a Note to explain the issue, and to refer directly to Trac #8783. The ticket has a string of forty-four comments, so presumably it's not a simple, obvious typo. What I fear is that in 5 yrs time someone will say "oh, there's a simpler way of doing this" and will un-do all your good work. Everyone: I'm know I get repetitive about this, but please always think about whether your change will seem as limpidly clear and obvious in five years time as it does now. ALWAYS add a reference to the ticket, unless you are simply fixing a totally stupid typo that nobody could possibly un-fix. (Stuff in the commit message is not enough, because you don't see it when you are looking at the source code. I enthusiastically encourage you to use the "Note" style, which you will see littered all over the compiler these days.) Pretty much any bug-fix is fixing something that wasn't obvious to the original author! Thank you all for making GHC so good. Simon | -----Original Message----- | From: ghc-commits [mailto:ghc-commits-bounces@haskell.org] On Behalf Of | git(a)git.haskell.org | Sent: 19 May 2014 06:11 | To: ghc-commits(a)haskell.org | Subject: [commit: ghc] master: Extract derived constants from nm output | for various OSes differently. (3df1c51) | | Repository : ssh://git@git.haskell.org/ghc | | On branch : master | Link : | http://ghc.haskell.org/trac/ghc/changeset/3df1c5109a6bd2a522717e524c10d8 | 42d4cd8ab8/ghc | | >--------------------------------------------------------------- | | commit 3df1c5109a6bd2a522717e524c10d842d4cd8ab8 | Author: Christian Maeder <Christian.Maeder(a)dfki.de> | Date: Thu Apr 3 10:00:07 2014 +0200 | | Extract derived constants from nm output for various OSes | differently. | | Fixes #8783. | | In order to avoid querying the nm version that does not work on Mac | OS X | we use the "nm -P" output that is supposed to produce (more | portable) | POSIX output and works on all tested OSes (MinGW, Mac OS X, Solaris | and | Linux using GNU nm) although slightly different (as documented). The | "nm | -P" output is actually only needed to recognize the output of a non- | GNU | Solaris nm (all other OSes produce sane outut using "nm" only). | | Signed-off-by: Austin Seipp <austin(a)well-typed.com> | | | >--------------------------------------------------------------- | | 3df1c5109a6bd2a522717e524c10d842d4cd8ab8 | utils/deriveConstants/DeriveConstants.hs | 37 +++++++++++++------------ | ------- | 1 file changed, 15 insertions(+), 22 deletions(-) | | diff --git a/utils/deriveConstants/DeriveConstants.hs | b/utils/deriveConstants/DeriveConstants.hs | index 8c943f0..6bfce24 100644 | --- a/utils/deriveConstants/DeriveConstants.hs | +++ b/utils/deriveConstants/DeriveConstants.hs | @@ -641,7 +641,7 @@ getWanted verbose tmpdir gccProgram gccFlags | nmProgram | oFile = tmpdir </> "tmp.o" | writeFile cFile cStuff | execute verbose gccProgram (gccFlags ++ ["-c", cFile, "-o", | oFile]) | - xs <- readProcess nmProgram [oFile] "" | + xs <- readProcess nmProgram ["-P", oFile] "" | let ls = lines xs | ms = map parseNmLine ls | m = Map.fromList $ catMaybes ms @@ -710,28 +710,21 @@ | getWanted verbose tmpdir gccProgram gccFlags nmProgram | doWanted (ClosurePayloadMacro {}) = [] | doWanted (FieldTypeGcptrMacro {}) = [] | | - -- parseNmLine parses nm output that looks like | - -- "0000000b C derivedConstantMAX_Vanilla_REG" | + -- parseNmLine parses "nm -P" output that looks like | + -- "derivedConstantMAX_Vanilla_REG C 0000000b 0000000b" (GNU | nm) | + -- "_derivedConstantMAX_Vanilla_REG C b 0" (Mac OS X) | + -- "_derivedConstantMAX_Vanilla_REG C 000000b" (MinGW) | + -- "derivedConstantMAX_Vanilla_REG D 1 b" | (Solaris) | -- and returns ("MAX_Vanilla_REG", 11) | - parseNmLine xs0 = case break (' ' ==) xs0 of | - (x1, ' ' : xs1) -> | - case break (' ' ==) xs1 of | - (x2, ' ' : x3) -> | - case readHex x1 of | - [(size, "")] -> | - case x2 of | - "C" -> | - let x3' = case x3 of | - '_' : rest -> | rest | - _ -> x3 | - in case stripPrefix prefix | x3' of | - Just name -> | - Just (name, size) | - _ -> Nothing | - _ -> Nothing | - _ -> Nothing | - _ -> Nothing | - _ -> Nothing | + parseNmLine line | + = case words line of | + ('_' : n) : "C" : s : _ -> mkP n s | + n : "C" : s : _ -> mkP n s | + [n, "D", _, s] -> mkP n s | + _ -> Nothing | + where mkP r s = case (stripPrefix prefix r, readHex s) of | + (Just name, [(size, "")]) -> Just (name, size) | + _ -> Nothing | | -- If an Int value is larger than 2^28 or smaller | -- than -2^28, then fail. | | _______________________________________________ | ghc-commits mailing list | ghc-commits(a)haskell.org | http://www.haskell.org/mailman/listinfo/ghc-commits

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