August 2009 - Glasgow-haskell-users

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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Three patches for cabal
by Niklas Broberg 09 Nov '09

09 Nov '09

(Trying again since my previous patches were too big for the list.) While doing a survey[1] of the extensions registered with Cabal, I came across two warts in the list of constructors, and one constructor that should be deprecated. First there's the constructor called TransformListComp, which should really be named GeneralizedListComp, since the constructor should describe the extension and not the implementation scheme. Second there's the constructor NoMonoPatBinds, which actually describes the default Haskell 98 behavior, even if GHC has a different default. It's GHC's behavior that is the extension, so the constructor in cabal should really be named MonoPatBinds. Also, the PatternSignatures constructor has been deprecated in GHC and superceded by ScopedTypeVariables. The attached patches (three in one file) adds the proposed new constructors, deprecates the old ones, and adds documentation. Cheers, /Niklas

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ANNOUNCE: GHC 6.8.3 Release Candidate
by Ian Lynagh 22 Sep '09

22 Sep '09

We are pleased to announce the Release Candidate phase for GHC 6.8.3. Snapshots beginning with 6.8.2.20080527 are release candidates for 6.8.3 You can download snapshots from here: http://www.haskell.org/ghc/dist/stable/dist/ Right now we have the source bundles: http://www.haskell.org/ghc/dist/stable/dist/ghc-6.8.2.20080527-src.tar.bz2 http://www.haskell.org/ghc/dist/stable/dist/ghc-6.8.2.20080527-src-extralib… Only the first of these is necessary. The "extralibs" package contains various extra packages that are often supplied with GHC - unpack the extralibs tarball on top of the source tree to add them, and they will be included in the build automatically. There is also currently an installer for i386/Windows and binary distributions for x86_64/Linux and i386/Linux. More may appear later. Please test as much as possible; bugs are much cheaper if we find them before the release! We expect to release in a few days, assuming no major issues are discovered. Thanks Ian, on behalf of the GHC team

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GHCi can't see 'atexit', can't load module
by Maurício CA 13 Sep '09

13 Sep '09

(I left this in cafe, but I think it is actually ghc related.) I just checked it seems not to be possible to load any module in GHCi that uses FFI to wrap the standard C function 'atexit'. When trying that, we get a message saying the symbol 'atexit' can't be found. (This is not a problem when building an executable with ghc, though.) It's easy to reproduce the problem. Just try something like this: ----- module XXX where import Foreign import Foreign.C foreign import ccall atexit :: FunPtr (IO ()) -> IO CInt ----- Load it in ghci (after ':set -XForeignFunctionInterface' to get FFI) and you will get the error. If we replace the line below for the above we don't get any error message: foreign import ccall exit :: CInt -> IO () Here, we just replaced 'atexit' by 'exit', which, according to 'nm' tool, is at the same 'libc' library that 'atexit' belongs to. Thanks, Maurício

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Build error in users guide in HEAD of today
by "Philip K.F. Hölzenspies" 11 Sep '09

11 Sep '09

Dear GHC-ers, I'm trying to put together a virtual machine with a default development for GHC hacking. To test it, I was running "sh validate" in the build tree. There were build errors in the doc/users_guide, however. Google gave me an hpaste page with the error on it, but I couldn't find the referring message. Does this ring a bell for anyone: latex failed users_guide_tmp.tex:1380: Undefined control sequence \Documents. users_guide_tmp.tex:1380: leading text: } users_guide_tmp.tex:1380: Undefined control sequence \user. users_guide_tmp.tex:1380: leading text: } users_guide_tmp.tex:5782: Undefined control sequence \Documents. users_guide_tmp.tex:5782: leading text: ...kurl{C: \Documents~And~Settings\user\ghc} users_guide_tmp.tex:5782: Undefined control sequence \user. users_guide_tmp.tex:5782: leading text: ...kurl{C: \Documents~And~Settings\user\ghc} users_guide_tmp.tex:5782: Undefined control sequence \ghc. users_guide_tmp.tex:5782: leading text: ...kurl{C: \Documents~And~Settings\user\ghc} users_guide_tmp.tex: File ended while scanning use of \hyper@n@rmalise. users_guide_tmp.tex: Emergency stop. Error: latex compilation failed make[2]: *** [docs/users_guide/users_guide.ps] Error 1 make[1]: *** [all_docs/users_guide] Error 2 I understand the LaTeX errors, but I'm not so well versed in docbook. Should the path in the ghci.xml and packages.xml be forward slashed, instead of backslashed or does this indicate there's something wrong with my docbook/latex setup? Even when I change the backslashes to forward slashes, the last error (scanning use of \hyper@n@rmalise) remains. Any ideas? Regards, Philip

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Libraries in the repo
by Simon Marlow 11 Sep '09

11 Sep '09

Simon and I have been chatting about how we accommodate libraries in the GHC repository. After previous discussion on this list, GHC has been gradually migrating towards having snapshots of libraries kept as tarballs in the repo (currently only "time" falls into this category), but I don't think we really evaluated the alternatives properly. Here's an attempt to do that, and to my mind the outcome is different: we really want to stick to having all libraries as separate repositories. Background: * Scope: libraries that are needed to build GHC itself (aka "boot libraries") * Boot libraries are of several kinds: - INDEPENDENT: Independently maintained (e.g. time, haskeline) - COUPLED: Tightly coupled to GHC, but used by others (base) - SPECIFIC: Totally specific to GHC (e.g. template-haskell, DPH) * Most boot libraries are INDEPENDENT. INDEPENDENT libraries have a master repository somewhere separate from the GHC repositories. * We need a branch of INDEPENDENT libraries, so that GHC builds don't break when the upstream package is modified. * Sometimes we want to make local modifications to INDEPENDENT libraries: - when GHC adds a new warning, we need to fix instances of the warning in the library to keep the GHC build warning-free. - to check that the changes work, before pushing upstream Choices for how we deal with libraries in the GHC repository: (+) is a pro, (-) is a con. (1) Check out the library from a separate repo, using the darcs-all script. The repo may either be a GHC-specific branch [INDEPENDENT], or the master copy of the package [SPECIFIC/COUPLED]. (+) we can treat every library this way, which gives a consistent story. Consistency is good for developers. (+) [INDEPENDENT] makes it easy to push changes upstream and sync with the upstream repo (unless upstream is using a different VCS). (-) [INDEPENDENT] we have to be careful not to let our branches get too far out of sync with upstream, and we must sync before releasing GHC. (2) Put a snapshot tarball of the library in libraries/tarballs, but allow you to checkout the darcs repo instead. (-) [SPECIFIC/COUPLED] this approach doesn't really make sense, because we expect to be modifying the library often. (-) updating the snapshot is awkward (-) workflow for making a change to the library is awkward: - checkout the darcs repo - make the change, validate it - push the change upstream (bump version?) - make a new snapshot tarball - commit the new snapshot to the GHC repo. (-) having tarballs in the repository is ugly (-) we have no revision history of the library (3) The GHC repo *itself* contains every library unpacked in the tree. You are allowed to check out the darcs repo instead. (+) atomic commits to both the library and GHC. (+) doing this consistently would allow us to remove darcs-all, giving a nice easy development workflow (-) [INDEPENDENT/COUPLED] still need a separate darcs repo. (-) [INDEPENDENT/COUPLED] pushing changes upstream is hard (-) [INDEPENDENT/COUPLED] manual syncing with upstream (-) [COUPLED] (particularly base) syncing with upstream would be painful. (3) works best for SPECIFIC libraries, whereas (1) works best for INDEPENDENT/COUPLED libraries. If we want to treat all libraries the same, then the only real option is (1). Experience with Cabal and bytestring has shown that (1) can work for INDPENDENT libraries, but only if we're careful not to get too out-of-sync (as we did with bytestring). In the case of Cabal, we never have local changes in our branch that aren't in Cabal HEAD, and that works well. Comments/thoughts? Cheers, Simon

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few questions about GHC RTS
by Peter Hercek 07 Sep '09

07 Sep '09

Hi, I thought I may look at the :next command for GHCi debugger again. If I do, I will not make it before 6.12.1 is out. I have few questions about RTS in relation to :next implementation. If they is easy to answer I would appreciate it, if not, don't bother since I'm not sure I'll do it ... and If I decide to do it I may just figure it out myself or fail again :) Why is stg_nofoceIO_info added as last argument to IO actions in unregistered mode? Do I still need to pass it in even when (I think) my IO action does not need it? E.g. is it required for every IO action by some stack walking code or something? Are there any Cmm functions in RTS with signature (IO()) or signature (Int->IO()) which I could check out as examples to see how they are done? ... and ideally also how they are called from the stack. Are there any special things to do when adding a new field (e.g. simulated stack size) to StgTSO? Thanks, Peter.

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Plans for GHC 6.12.1: release candidate 14 September 2009
by Ian Lynagh 26 Aug '09

26 Aug '09

Hi all, This is a summary of our plans for GHC 6.12.1. We are aiming to have the first release candidate out on the 14th September 2009. Until then, we plan to focus on the bugs in the 6.12.1 milestone, marked high priority; they are listed here: http://hackage.haskell.org/trac/ghc/query?status=new&status=assigned&status… If there is a bug not in that list that is important to you, please let us know. Thanks Ian

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ghc 6.10.4 infix declarations and '\' bug or not ?
by John Lask 22 Aug '09

22 Aug '09

in declaring fixity for an operator (\\) to get it to compile using ghc 6.10.4, I needed to use the following code infixl 9 \\\ (\\) a b = etc ... where I assume the first \ escapes the second \, using infixl 9 \\ generates a syntax error infixl 9 \\ used to compile no problems with ghc 6.8.2 what is going on here ? why do I now need to add an additional \ ?, where is this change documented ?, is this a bug?

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RE: [Haskell-cafe] generalize RecordPuns and RecordWildCards to work with qualified names?
by Simon Peyton-Jones 20 Aug '09

20 Aug '09

Evan, Lennart Thanks for the provocation. I've committed a patch that fixes all these issues. Try now! Simon Thu Aug 20 13:34:43 BST 2009 simonpj(a)microsoft.com * Improvements to record puns, wildcards * Make C { A.a } work with punning, expanding to C { A.a = a } * Make it so that, with -fwarn-unused-matches, f (C {..}) = x does not complain about the bindings introduced by the "..". * Make -XRecordWildCards implies -XDisambiguateRecordFields. * Overall refactoring of RnPat, which had become very crufty. In particular, there is now a monad, CpsRn, private to RnPat, which deals with the cps-style plumbing. This is why so many lines of RnPat have changed. * Refactor the treatment of renaming of record fields into two passes - rnHsRecFields1, used both for patterns and expressions, which expands puns, wild-cards - a local renamer in RnPat for fields in patterns - a local renamer in RnExpr for fields in construction and update This make it all MUCH easier to understand * Improve documentation of record puns, wildcards, and disambiguation | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On | Behalf Of Evan Laforge | Sent: 12 August 2009 23:59 | To: Simon Peyton-Jones | Cc: Augustsson, Lennart; haskell; GHC users | Subject: Re: [Haskell-cafe] generalize RecordPuns and RecordWildCards to work with | qualified names? | | > | Even is suggesting that instead of reporting an error, in the second | > | case we could use the translation: | > | | > | f (A.A { A.a }) = a --> f (A.A { A.a = a }) | > | | > | (i.e., when punning occurs with a qualified name, use just the | > | unqualified part of the name in the pattern) | > | > Yes, that'd be possible. But it seems debatable -- it doesn't *look* as if the | pattern (A.A { A.a }) binds 'a' -- and it seems even less desirable in record | construction and update. To be concrete, would you expect these to work too? | > | > g a = A.A { A.a } --> g a = A.A { A.a = a } | > h x a = x { A.a } --> h x a = a { A.a = a } | | Oh, I didn't realize that record punning included construction as | well. Yeah, that's a little funky looking. I don't mind seeing the | binding form and I think a new reader could figure it out without too | much trouble but I would be a little confused by the construction form | and think a new reader would also be confused. | | > With -XDisambiguateRecordFields you could say | > | > g a = A.A { a } | > | > which seems better. (But there's no help for record update, since we don't know | which data constructor is involved.) | | I didn't know about DisambiguateRecordFields! Looks like that also | makes the wildcard work like I want it to. | | The ghc docs for DisambiguateRecordFields don't make this very clear | to me... it talks about disambiguating names in scope, but if I say | "R.R { a = val}" I wouldn't expect it to "disambiguate" 'a', which is | not in scope at all, to 'R.a' which looks like a completely different | name. Rereading the paragraph at 7.3.11 I'm still surprised this | works. Maybe add something like: | | ... preceeding docs ... | | This also means that if you use qualified imports you can still use | unqualified field names. E.g. in the pattern @(R.R { a = a_val })@, | @a@ will be disambiguated to @R.a@, even if @R@ is imported qualified. | | I gather we're not supposed to call them "records" anymore, they're | supposed to be something I forget now, but the rest of the ghc docs | says records, so... | | > So my current conclusion is: improve the error message, perhaps suggesting the | flag -XDismabiguateRecordFields, but don't add the change you suggest. | > | > Comments? | | Sounds good to me. I'll try adding DisambiguateRecordFields and try | out the new punning, thanks! | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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