July 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 Also, the PatternSignatures constructor has been deprecated in GHC and superceded by ScopedTypeVariables.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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Generating valid Haskell code using the GHC API pretty printer
by Jan Schaumlöffel 18 Aug '09

18 Aug '09

Hello everyone, we are trying to use the GHC API for a source-to-source transformation on Haskell programs. The result of parsing and typechecking a module enables us to apply the transformation, but writing the transformed module back using the pretty printer (Outputable) generates invalid Haskell code. For one thing, since even the names defined in the current module are fully qualified, the resulting code is not valid anymore. This can be worked around, but there is another issue: Simply reading the following program and then writing it out using the pretty printer renders the resulting code invalid. > module Main where > main = do > if True then putStrLn "longlonglonglonglonglongline" > else return () > longlonglonglonglonglonglonglonglonglonglonglongname $ "test" > longlonglonglonglonglonglonglonglonglonglonglongname = putStrLn The result looks like this: > Main.main = do if GHC.Bool.True then > System.IO.putStrLn "longlonglonglonglonglongline" > else > GHC.Base.return () > Main.longlonglonglonglonglonglonglonglonglonglonglongname > GHC.Base.$ > "test" > Main.longlonglonglonglonglonglonglonglonglonglonglongname = System.IO.putStrLn There are two different problems in this output: 1) the indentation of "if ... then ... else" violates the "do"-block layout rule 2) the indentation of the long function call is invalid It looks like those problems could be avoided if the pretty printer could be configured to consistently use "do { ... ; ... }" notation, but we have been unable to figure out how. Is there a canonical way to use the GHC API to pretty print to valid Haskell code? Kind regards, Jan Appended is our current code to execute the transformation above (the module to be read is expected in a file "dummy.hs" for simplicity). Please excuse if this might not be a minimal example. module Main where import GHC import GHC.Paths import Outputable main = do x <- runGhc (Just libdir) $ do dflags <- getSessionDynFlags setSessionDynFlags (dflags { hscTarget = HscNothing, ghcLink = NoLink }) target <- guessTarget "dummy.hs" Nothing setTargets [target] load LoadAllTargets graph <- getModuleGraph let unparsedmod = head graph parsedmod <- parseModule unparsedmod typecheckedmod <- typecheckModule parsedmod let Just renamedsource = renamedSource typecheckedmod (group,_,_,_,_) = renamedsource moduledings = (ms_mod unparsedmod) return (showSDoc (ppr group)) putStr $ x ++ "\n" -- If you're happy and you know it, syntax error!

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Re: Haskell Platform 2009.2.0.2
by Christian Maeder 10 Aug '09

10 Aug '09

Don Stewart wrote: > Heads up lads, we're about 24 hours from Haskell Platform 2009.2.0.2 > > http://code.haskell.org/haskell-platform/haskell-platform.cabal I still see time ==1.1.2.4, although ghc-6.10.4 comes with: time-1.1.4 http://trac.haskell.org/haskell-platform/ticket/74 Is this on purpose (possibly installing two time versions)? I only know that time-1.1.4 and time-1.1.3 supply more Typeable instances (which may break existing code) Cheers Christian

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GHC 6.10.2 consuming lots of memory while compiling - help?
by Justin Bailey 06 Aug '09

06 Aug '09

I apologize in advance for the vagueness of my report here - it's one of those situations I'm not sure how to cut it down to size yet. I have a module that uses HaskellDB and Template Haskell together. The module itself depends on 23 other modules, each of which give a type definition for a particular database table or view. I only mention that to emphasize that the module depends on some "big" types (HList records w/ 20+ members) and on compile-time generated code. My problem is this - when GHC compile the module, it consumes 1.2 GB of memory, takes about 10 minutes, and finally produces an object file. The memory usage seems related to template haskell, but I'm not positive. I've attached verbose output from compiling the module in question. The command line I used was: ghc -v --make -c DeliveryManagementQueries.hs -XEmptyDataDecls -XTypeSynonymInstances -XTemplateHa skell Now for my question - please ignore the specifics of haskelldb/template haskell - any suggestions for figuring out what GHC is doing, besides tried-and-true divide and conquer? Justin

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Working with GHC HEAD
by Antoine Latter 04 Aug '09

04 Aug '09

Folks, I was trying to see what GHC head was like, but I've run into a few snags compiling packages. My existing binary for cabal-install can install quite a few packages, but then starts giving me strange errors eventually: >>> $ cabal --version cabal-install version 0.6.2 using version 1.6.0.1 of the Cabal library $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.11.20090724 $ cabal install zlib Resolving dependencies... Configuring zlib-0.5.2.0... ghc-stage2: /home/alatter/.ghc/x86_64-linux-6.11.20090724/package.conf:6:163: parse error on input `Nothing' cabal: Error: some packages failed to install: zlib-0.5.2.0 failed during the configure step. The exception was: exit: ExitFailure 1 <<< If I then do: >>> $ mv /home/alatter/.ghc/x86_64-linux-6.11.20090724/package.conf /home/alatter/.ghc/x86_64-linux-6.11.20090724/package.conf.back $ cabal install zlib <<< Everything works great. After looking at the package.conf being complained about, the last line looks like so: >>> InstalledPackageInfo {package = PackageIdentifier {pkgName = PackageName "cpphs", pkgVersion = Version {versionBranch = [1,7], versionTags = []}}, license = LGPL Nothing, copyright = "2004-8, Malcolm Wallace", maintainer = "Malcolm Wallace <Malcolm.Wallace(a)cs.york.ac.uk>", author = ... <<< Not the license field of the package info - we have "license = LGPL Nothing, copright ...". I thought that maybe since GHC head ships with the new dev version of Cabal, I need the dev version of cabal-install to properly install packages. However cabal-install (and most of the things I want to test out) require the 'network' package, which doesn't build against GHC head (System.Posix.Internals doesn't exist, and the functionality that 'network' uses from there now lives in GHC.IO.* and is much changed). So a few things: - Should I expect the stable version of cabal-install built against GHC 6.10 to work for head? Are the errors I'm getting expected? - Does anyone have a version of 'network' which builds against GHC head? I could bludgeon in the new GHC.IO.FD.FD type myself, but I'd thought I'd ask around first. Thanks, Antoine

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Attempted install on Mac OS X - recent versions - FAIL
by Phil Dennis 29 Jul '09

29 Jul '09

I am looking for some assistance with installing GHC on Mac OS X. If there is a more appropriate place for me to ask, please let me know. I have tried, with no luck so far, the 2 different binary distributions of 6.10.4 provided for the Mac on the haskell.org ghc download page (http://www.haskell.org/ghc/download_ghc_6_10_4.html#macosxintel) I have OS X version 10.5.7 with XCode version 3.1.2 installed. When I run the installer (GHC-6.10.4-i386.pkg) I get as far as the "Installation Type" screen with the following text displayed: "Click Install to perform a standard installation of this software for all users of this computer". However the 'Install' button is greyed out and cannot be clicked. The last entries in the installer log are as follows: Jul 29 00:03:29 phil-denniss-macbook-pro Installer[11740]: Glasgow Haskell Compiler Installation Log Jul 29 00:03:29 phil-denniss-macbook-pro Installer[11740]: Opened from: /Users/pjdennis/Downloads/GHC-6.10.4-i386.pkg Jul 29 00:03:30 phil-denniss-macbook-pro installdb[11743]: started (uid 96) Jul 29 00:03:30 phil-denniss-macbook-pro installdb[11743]: Opened receipt database on '/' with schema 17. Jul 29 00:03:36 phil-denniss-macbook-pro installdb[11743]: done. (0.003u + 0.003s) ALSO I tried the binary distribution (ghc-6.10.4-i386-apple-darwin.tar.bz2) which I extracted, and then ran ./configure, as instructed in the INSTALL file. After adding /Developer/usr/bin to the path (so that the configure script could find the 'ar' program) I now get the following error from the configure script: configure: error: C compiler cannot create executables See `config.log' for more details. I have pasted some of what looks relevant from config.log, below. Any help with either one of the install methods for OS X would be much appreciated. I am keen to get started trying out Haskell, instead of mucking with installers. Regards, Phil Dennis --------------------------------------------------------------- >From config.log configure:2298: found /Developer/usr/bin/gcc configure:2309: result: gcc configure:2547: checking for C compiler version configure:2554: gcc --version >&5 i686-apple-darwin9-gcc-4.0.1 (GCC) 4.0.1 (Apple Inc. build 5490) Copyright (C) 2005 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. configure:2557: $? = 0 configure:2564: gcc -v >&5 Using built-in specs. Target: i686-apple-darwin9 Configured with: /var/tmp/gcc/gcc-5490~1/src/configure --disable-checking -enable-werror --prefix=/usr --mandir=/share/man --enable-languages=c,objc,c++,obj-c++ --program-transform-name=/^[cg][^.-]*$/s/$/-4.0/ --with-gxx-include-dir=/include/c+ +/4.0.0 --with-slibdir=/usr/lib --build=i686-apple-darwin9 --with-arch=apple --with-tune=generic --host=i686-apple-darwin9 --target=i686-apple-darwin9 Thread model: posix gcc version 4.0.1 (Apple Inc. build 5490) configure:2567: $? = 0 configure:2574: gcc -V >&5 gcc-4.0: argument to `-V' is missing configure:2577: $? = 1 configure:2600: checking for C compiler default output file name configure:2627: gcc conftest.c >&5 ld: library not found for -lcrt1.10.5.o collect2: ld returned 1 exit status configure:2630: $? = 1 configure:2668: result: configure: failed program was: | /* confdefs.h. */ | #define PACKAGE_NAME "" | #define PACKAGE_TARNAME "" | #define PACKAGE_VERSION "" | #define PACKAGE_STRING "" | #define PACKAGE_BUGREPORT "" | /* end confdefs.h. */ | | int | main () | { | | ; | return 0; | } configure:2675: error: C compiler cannot create executables See `config.log' for more details.

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ANNOUNCE: GHC version 6.10.4
by Ian Lynagh 28 Jul '09

28 Jul '09

============================================================== The (Interactive) Glasgow Haskell Compiler -- version 6.10.4 ============================================================== The GHC Team is pleased to announce a new patchlevel release of GHC. This release contains a number of bugfixes relative to 6.10.3, so we recommend upgrading. Release notes are here: http://haskell.org/ghc/docs/6.10.4/html/users_guide/release-6-10-4.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; the current language version is Haskell 98, agreed in December 1998 and revised December 2002. 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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[reiner.pope@gmail.com: [Haskell-cafe] SpecConstr difficulties]
by Don Stewart 28 Jul '09

28 Jul '09

Something for SimonPJ ----- Forwarded message from Reiner Pope <reiner.pope(a)gmail.com> ----- Date: Mon, 20 Jul 2009 22:09:09 +0930 From: Reiner Pope <reiner.pope(a)gmail.com> To: Haskell Cafe mailing list <haskell-cafe(a)haskell.org> Subject: [Haskell-cafe] SpecConstr difficulties Hi everyone, I've been having some trouble getting SpecConstr to work as I want it to. The following example (see end of email) came up in some code I was playing around with. The loops g1 and g2 both compute the same thing: the maximum element of the "list" (which has been fused away) of numbers from 1 to 10. Since 'maximum' is a foldl1 not a foldl, I use a strict Maybe type as an accumulator. The Maybe gets filled after the first element is seen, so the Maybe is a Just for almost the entire running of the loop. It would be good to have this recognised by SpecConstr, to create an optimised loop for the Just case. This does indeed happen for g1, but not for g2. My difficulty is that I am only able to produce code similar to g2, i.e. where the pattern matching is in a separate function, 'expose', because the 'expose' function is implemented in a type-class, like in stream-fusion. Is there some way to keep the SpecConstr while leaving the 'expose' as a separate function? Here is the code: > {-# LANGUAGE BangPatterns #-} > > module Test(ans1,ans2) where > > import Prelude hiding(Maybe(..)) > > data Maybe a = Just !a | Nothing > > Nothing `mapp` Just b = Just b > Just a `mapp` Just b = Just (max a b) > > ans1 = g1 Nothing (0::Int) > > g1 m !n = case m of > Nothing -> if n > 10 then m else g1 (m `mapp` Just n) (n+1) > Just x -> if n > 10 then m else g1 (m `mapp` Just n) (n+1) > > ans2 = g2 Nothing (0::Int) > > g2 m !n = expose m (if n > 10 then m else g2 (m `mapp` Just n) (n+1)) > expose Nothing b = b > expose (Just a) b = a `seq` b On a similar note, when I was having difficulties with this problem, I started to wonder if it would be possible to come up with a more direct way to tell GHC, "do SpecConstr on this variable". From reading the source code of the stream-fusion package, it seems that the current way of doing this is with 'expose' functions like I wrote below. Could we instead have a {-# SPECCONSTR #-} pragma, to be used on function arguments, like: foo {-# SPECCONSTR #-} x y {-# SPECCONSTR #-} z = ... This pragma should say to the GHC something like "ignore conditions H2, H5 and H6 of the SpecConstr paper, for this function and this argument". Cheers, Reiner _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ----- End forwarded message -----

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