October 2011 - Glasgow-haskell-users

Records in Haskell
by Simon Peyton-Jones 27 Mar '12

27 Mar '12

Friends Provoked the (very constructive) Yesod blog post on "Limitations of Haskell", and the follow up discussion, I've started a wiki page to collect whatever ideas we have about the name spacing issue for record fields. http://hackage.haskell.org/trac/ghc/wiki/Records As Simon M said on Reddit, this is something we'd like to fix; but we need a consensus on how to fix it. Simon

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ANNOUNCE: GHC version 7.2.1
by Ian Lynagh 27 Mar '12

27 Mar '12

============================================================= The (Interactive) Glasgow Haskell Compiler -- version 7.2.1 ============================================================= The GHC Team is pleased to announce a new major release of GHC, 7.2.1. The 7.2 branch is intended to be more of a "technology preview" than normal GHC stable branches; in particular, it supports a significantly improved version of DPH, as well as new features such as compiler plugins and "safe Haskell". The design of these new features may evolve as we get more experience with them. See the release notes for more details of what's new and what's changed. We are also using this branch as an opportunity to work out the best workflows to use with git. We expect the 7.2 branch to be short-lived, with 7.4.1 coming out shortly after ICFP as normal. Full release notes are here: http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/release-7-2-1.html How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces (C, whatever). GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://hackage.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://hackage.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://hackage.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://hackage.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see http://www.haskell.org/mailman/listinfo/ Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

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partially applied type synonyms
by Arie Peterson 05 Mar '12

05 Mar '12

Dear list, Is there a good reason that partially applied type synonyms cannot be made instances of classes? - A simple example would be making the identity type 'Id' ("type Id x = x") instance of 'Monad'. This would eliminate the need for some silly occurrences of 'runIdentity', and perhaps narrow the gap between monads and monad transformers. - The reason I complain about this now is a more involved example, where introducing a newtype to work around the restriction is not an option. Well, not as far as I can see now, anyway. Partially applied type synonyms are, in a sense, the anonymous functions at the type level, and one might argue that they deserve the same 'first-class member status' as the lambda at the value level. Kind regards, Arie Peterson

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ANNOUNCE: GHC 7.2.1 Release Candidate 1
by Ian Lynagh 11 Feb '12

11 Feb '12

We are pleased to announce the first release candidate for GHC 7.2.1: http://www.haskell.org/ghc/dist/7.2.1-rc1/ This includes the source and testsuite tarballs, installers for OS X and Windows, and bindists for amd64/Linux, i386/Linux, amd64/FreeBSD and i386/FreeBSD. Please test as much as possible; bugs are much cheaper if we find them before the release! Thanks Ian, on behalf of the GHC team

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Proposal to incorporate Haskell.org
by Don Stewart 16 Dec '11

16 Dec '11

Hello everyone. The haskell.org committee[1], in the interest of the long-term stability of the open source Haskell community infrastructure, has decided to incorporate haskell.org as a legal entity. This email outlines our recommendation, and seeks input from the community on this decision. The committee's proposal is that haskell.org incorporate as an entity under the Software Freedom Conservancy umbrella organization (the same group that Darcs joined recently): http://sfconservancy.org/ If we proceed with this move, haskell.org will be a legal entity, and registered as a non-profit, allowing us to more directly accept (US tax-deductible) donations, and to invest in assets that benefit the Haskell open source community. We welcome your feedback on the proposal attached below. -- Don Stewart (on behalf of the Haskell.org committee) ------------------------------------------------------------------------ = A proposal for the incorporation of Haskell.org = In recent years, haskell.org has started to receive assets, e.g. money from Google Summer Of Code, donations for Hackathons, and a Sparc machine for use in GHC development. We have also started spending this money: in particular, on hosting haskell.org itself. There is also interest in running fundraising drives for specific things such as Hackathon sponsorship and hosting fees. However, haskell.org doesn't currently exist as a legal entity, meaning that these assets have had to be held on our behalf by other entities, such as Galois and various universities. This leads to tricky situations, with no-one being sure who should decide how the haskell.org assets can be used. To solve these problems, we propose that haskell.org applies to become a member project of the Software Freedom Conservancy (SFC) <http://conservancy.softwarefreedom.org/>. The SFC is a non-profit organization that provides free financial and administrative services to open source projects. Additionally, it has 501(c)(3) status, meaning donations from the US are tax-deductible. The SFC would hold haskell.org's money and other assets, and would be able to accept donations on behalf of haskell.org. The haskell.org committee, as described here [2], will make decisions on spending assets and other decisions related to governing the non-profit. Before proceeding, we are inviting input from the community in the form of specific objections or queries regarding the plan. We've tried to answer some of the most likely questions: Q: Does this mean that my Haskell project must now be covered by a copyleft licence such as GPL? A: No, but Haskell projects using haskell.org resource should use an Open Source licence <http://www.opensource.org/licenses/alphabetical>. Q: Will it still be possible to use community.h.o to host non-open-source material, such as academic papers? A: An overall minority of such content, as is the current situation, is not a problem. Q: Will it still be possible to have job ads on the haskell.org mailing lists and website? A: Yes. Q: Will this affect our ability to host the Haskell Symposium <http://www.haskell.org/haskell-symposium/> and Industrial Haskell Group<http://industry.haskell.org/> webpages within haskell.org? A: No. Q: What will be the relationship between haskell.org and other organizations such as the Haskell Symposium and Industrial Haskell Group? A: Those organisations will continue to exist as separate entities. Q: If an umbrella non-profit organisation "The Haskell Foundation" was created, would haskell.org be able to join it? A: Yes. It's likely that in such a scenario, the Haskell Foundation would become the owner of the haskell.org domain name, with the cost divided between the members. The entity that is part of the SFC would be renamed "community.haskell.org" in order to avoid confusion. [1]: http://www.haskell.org/haskellwiki/Haskell.org_committee [2]: http://www.haskell.org/haskellwiki/Haskell.org_committee#Operation

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Linker flags --hash-style=both --no-copy-dt-needed-entries --as-needed
by Joachim Breitner 31 Oct '11

31 Oct '11

Dear GHC team, Ubuntu applies the following patch to the ghc package¹: diff -pruN 7.0.4-8/aclocal.m4 7.0.4-8ubuntu1/aclocal.m4 --- 7.0.4-8/aclocal.m4 2011-10-31 16:22:09.000000000 +0000 +++ 7.0.4-8ubuntu1/aclocal.m4 2011-10-31 16:22:20.000000000 +0000 @@ -109,6 +109,10 @@ AC_DEFUN([FPTOOLS_SET_C_LD_FLAGS], $4="$$4 -arch x86_64" $5="$$5 -m64" ;; + *-linux*) + $3="$$3 -Wl,--hash-style=both,--no-copy-dt-needed-entries,--as-needed" + $4="$$4 --hash-style=both --no-copy-dt-needed-entries --as-needed" + ;; esac # If gcc knows about the stack protector, turn it off. and it was requested² that this should be done in Debian as well. I generally feel uneasy diverging from upstream, as it could make debugging harder, so I’m contacting you first whether you might be interested in applying the change to ghc proper. I did not dig deep into the reason behind the patch, but http://wiki.debian.org/ToolChain/DSOLinking seems to give some reasons, and the author of the patch, Matthias Klose, is CCed. Greetings, Joachim ¹ http://patches.ubuntu.com/g/ghc/ghc_7.0.4-8ubuntu1.patch ² http://lists.debian.org/debian-haskell/2011/10/msg00066.html -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

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Type error: Expected type: T. Actual type T ???
by Bas van Dijk 31 Oct '11

31 Oct '11

Hello, I'm working on a new design of monad-control[1]. However I get a type error I don't understand. Here's an isolated example: {-# LANGUAGE UnicodeSyntax, RankNTypes, TypeFamilies #-} class MonadTransControl t where type St t ∷ * → * liftControl ∷ Monad m ⇒ (Run t → m α) → t m α restore ∷ Monad o ⇒ St t γ → t o γ type Run t = ∀ n β. Monad n ⇒ t n β → n (St t β) foo :: (Monad m, MonadTransControl t) => (Run t -> m α) -> t m α foo f = liftControl f Type checking 'foo' this gives the following error: Couldn't match expected type `Run t' with actual type `Run t' Expected type: Run t -> m α Actual type: Run t -> m α In the first argument of `liftControl', namely `f' In the expression: liftControl f When I remove the type annotation of 'foo' the program type checks. But when I ask ghci the type of 'foo' it tells me it's the same type: > :t foo foo :: (Monad m, MonadTransControl t) => (Run t -> m α) -> t m α Is this a bug in GHC? I'm using ghc-7.2.1. Regards, Bas [1] http://hackage.haskell.org/package/monad-control

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Errors building HEAD
by Johan Tibell 25 Oct '11

25 Oct '11

Hi, Trying to build HEAD from a clean tree I get: "/usr/bin/ghc" -H64m -O -fasm -package-conf libraries/bootstrapping.conf -package-name ghc-7.3 -hide-all-packages -i -icompiler/basicTypes -icompiler/cmm -icompiler/codeGen -icompiler/coreSyn -icompiler/deSugar -icompiler/ghci -icompiler/hsSyn -icompiler/iface -icompiler/llvmGen -icompiler/main -icompiler/nativeGen -icompiler/parser -icompiler/prelude -icompiler/profiling -icompiler/rename -icompiler/simplCore -icompiler/simplStg -icompiler/specialise -icompiler/stgSyn -icompiler/stranal -icompiler/typecheck -icompiler/types -icompiler/utils -icompiler/vectorise -icompiler/stage1/build -icompiler/stage1/build/autogen -Icompiler/stage1/build -Icompiler/stage1/build/autogen -Icompiler/stage1 -Icompiler/../libraries/base/cbits -Icompiler/../libraries/base/include -Icompiler/. -Icompiler/parser -Icompiler/utils -optP-include -optPcompiler/stage1/build/autogen/cabal_macros.h -package Cabal-1.11.3 -package array-0.3.0.2 -package base-4.3.1.0 -package bin-package-db-0.0.0.0 -package bytestring-0.9.1.10 -package containers-0.4.0.0 -package directory-1.1.0.0 -package filepath-1.2.0.0 -package hoopl-3.8.7.2 -package hpc-0.5.1.0 -package old-time-1.0.0.6 -package process-1.0.1.5 -package unix-2.4.2.0 -Wall -fno-warn-name-shadowing -fno-warn-orphans -XHaskell98 -XCPP -XMagicHash -XUnboxedTuples -XPatternGuards -XForeignFunctionInterface -XEmptyDataDecls -XTypeSynonymInstances -XMultiParamTypeClasses -XFlexibleInstances -XRank2Types -XScopedTypeVariables -XDeriveDataTypeable -DSTAGE=1 -Rghc-timing -O -fasm -no-user-package-conf -rtsopts -odir compiler/stage1/build -hidir compiler/stage1/build -stubdir compiler/stage1/build -hisuf hi -osuf o -hcsuf hc -c compiler/prelude/PrelNames.lhs -o compiler/stage1/build/PrelNames.o <<ghc: 1246932544 bytes, 43 GCs, 9388809/19990512 avg/max bytes residency (5 samples), 83M in use, 0.00 INIT (0.00 elapsed), 0.85 MUT (0.97 elapsed), 0.25 GC (0.26 elapsed) :ghc>> make[1]: *** No rule to make target `libraries/Cabal/cabal/dist-boot/build/Distribution/Version.hi', needed by `compiler/stage1/build/PackageConfig.o'. Stop. make: *** [all] Error 2 Mac OS X 10.7.2 (not that I think it matters in this case). -- Johan

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:kind broken in HEAD
by Sean Leather 25 Oct '11

25 Oct '11

It seems like :kind is broken in the HEAD ghci: *Main> :kind Maybe Top level: Expecting an ordinary type, but found a type of kind * -> * In a type expected by the context: Maybe *Main> Simon, could this be related to your change for :kind! ? Regards, Sean

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Discussion about the ConstraintKinds extension
by bob zhang 22 Oct '11

22 Oct '11

Hi all, I have played quite a bit with the ConstraintKinds extension, pretty cool. But I found a problem which I thought would be made better, plz correct me if I am wrong take a contrived example, class C B => B a where here B :: * -> Constraint, I think this definition is reasonable, since B does not appears in the first position of the context. Previously, we require acyclic class declarations since we don't have ConstraintKinds extension but now since type class could be abstracted, I think the definition above should be ok. the ghc-manual cited the program below is valid class C a where {op :: D b => a -> b -> b} class C a => D a where { ... } I think there are no reasons to reject class C B => B where (and this style is pretty useful in some cases) ... B :: * -> Constraint C :: (*->Constraint) -> Constraint Any comments are welcome -- Best, bob

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