December 2011 - Glasgow-haskell-users

Occasional segfault in GHCi w/ 7.4.1-rc1 and 64bit OS X
by austin seipp 17 Jul '12

17 Jul '12

Hello GHC hackers, I have been trying the recent 7.4.1-rc1 release on my OSX Snow Leopard machine. I am using the 64bit OSX .tar.bz. I used virthualenv/hsenv to set up a virtual environment to test packages with the RC, but I discovered that GHCi seems to segfault somewhat randomly when invoked. I cannot reproduce this problem with 7.0.4 (64bit,) 7.2.2 (64bit,) or 7.5.20111223 (also 64bit.) I have invoked GHCi probably a hundred times each, and have never had it crash. I can crash the RC fairly reliably however. I looked at the shell scripts that invoke GHC and ran GDB with the proper arguments. I got a backtrace like so: $ gdb /Users/a/vh-741-rc1_2/.hsenv/ghc/lib/ghc-7.4.0.20111219/ghc GNU gdb 6.3.50-20050815 (Apple version gdb-1518) (Sat Feb 12 02:52:12 UTC 2011) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "x86_64-apple-darwin"...Reading symbols for shared libraries .... done warning: Could not find object file "/Users/ian/zz64/ghc-7.4.0.20111219/rts/dist/build/libHSrts_thr.a(ffi64.o)" - no debug information available for "../src/x86/ffi64.c". warning: Could not find object file "/Users/ian/zz64/ghc-7.4.0.20111219/rts/dist/build/libHSrts_thr.a(prep_cif.o)" - no debug information available for "../src/prep_cif.c". warning: Could not find object file "/Users/ian/zz64/ghc-7.4.0.20111219/rts/dist/build/libHSrts_thr.a(types.o)" - no debug information available for "../src/types.c". (gdb) r -B/Users/a/vh-741-rc1_2/.hsenv/ghc/lib/ghc-7.4.0.20111219 --interactive Starting program: /Users/a/vh-741-rc1_2/.hsenv/ghc/lib/ghc-7.4.0.20111219/ghc -B/Users/a/vh-741-rc1_2/.hsenv/ghc/lib/ghc-7.4.0.20111219 --interactive Reading symbols for shared libraries + done GHCi, version 7.4.0.20111219: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x00000000ae21cf68 0x00000001ae2060da in evacuate1 () (gdb) bt #0 0x00000001ae2060da in evacuate1 () #1 0x00000001ae20b868 in scavenge_block1 () Previous frame inner to this frame (gdb could not unwind past this frame) (gdb) So it looks like a GC bug at first glance, but I haven't done rigorous investigation. Again this doesn't happen every time - probably 1/3 the time it crashes, the other 2/3 the time it seems to work fine. This naturally also affects `runghc`. Is this a known issue? Or should I file a bug and investigate further? Perhaps something forgot to get something merged into the 7.4 branch? -- Regards, Austin

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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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ghc-7.4.1-rc1 recompilation checking
by Christian Maeder 30 Jan '12

30 Jan '12

Hi, full recompilation with ghc-7.4.1-rc1 is already triggered by a changed "-o" option, which is inconvenient when creating different binaries with shared modules. (see below) It is no problem if I always omit the -o option and get binaries named like my input file, though. Can/should this behaviour of ghc-7.4 be relaxed? Cheers Christian -bash-3.00$ ghc B -o b [1 of 2] Compiling C ( C.hs, C.o ) [2 of 2] Compiling Main ( B.hs, B.o ) Linking b ... -bash-3.00$ ghc A -o a [1 of 2] Compiling C ( C.hs, C.o ) [2 of 2] Compiling Main ( A.hs, A.o ) Linking a ...

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ANNOUNCE: GHC 7.4.1 Release Candidate 1
by Ian Lynagh 17 Jan '12

17 Jan '12

We are pleased to announce the first release candidate for GHC 7.4.1: http://www.haskell.org/ghc/dist/7.4.1-rc1/ This includes the source tarball, 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! The release notes are not yet available, but here are some of the highlights of the 7.4 branch since 7.2 and 7.0: * There is a new feature Safe Haskell (-XSafe, -XTrustworthy, -XUnsafe): http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/safe-haskell.h… The design has changed since 7.2. * There is a new feature kind polymorphism (-XPolyKinds): http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/kind-polymorph… A side-effect of this is that, when the extension is not enabled, in certain circumstances kinds are now defaulted to * rather than being inferred. * There is a new feature constraint kinds (-XConstraintKinds): http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/constraint-kin… * It is now possible to give any sort of declaration at the ghci prompt: http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/interactive-ev… For example, you can now declare datatypes within ghci. * The profiling and hpc implementations have been merged and overhauled. Visible changes include renaming of profiling flags: http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/flag-reference… and the cost-centre stacks have a new semantics, which should in most cases result in more useful and intuitive profiles. The +RTS -xc flag now also gives a stack trace. * It is now possible to write compiler plugins: http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/compiler-plugi… * DPH support has been significantly improved. * There is now preliminary support for registerised compilation using LLVM on the ARM platform. Note: The release candidate accidentally includes the random, primitive, vector and dph libraries. The final release will not include them. Thanks Ian, on behalf of the GHC team

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Unexpected list non-fusion
by wren ng thornton 14 Jan '12

14 Jan '12

I've noticed that take and filter are good producers (and consumers) for list fusion, but takeWhile, drop, and dropWhile are not. Is there any reason for this discrepancy? If not, would I need to go through the libraries@ process for fixing it, or should I just submit a patch? -- Live well, ~wren

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Re: Records in Haskell
by Matthew Farkas-Dyck 12 Jan '12

12 Jan '12

Certainly not no conflicts: lambda expressions. On 30/12/2011, Colin Adams <colinpauladams(a)gmail.com> wrote: > On 30 December 2011 15:55, Matthew Farkas-Dyck <strake888(a)gmail.com> wrote: > >> On 30/12/2011, Andriy Polischuk <quuxity(a)gmail.com> wrote: >> > Yet another idea: >> > Consider using '\' as record access operator. No conflicts with anything >> at >> > all, and, >> > moreover, it really looks like hierarchical access. Reminds of >> filesystems >> > though. >> >> I hope this is a joke. >> > > Why? >

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Unit unboxed tuples
by Simon Peyton-Jones 10 Jan '12

10 Jan '12

Dear GHC users I've just discovered something very peculiar with unboxed tuples in GHC. f2 x = (# True, False #) f1 x = (# True #) f0 x = (# #) What types do these functions have? f2 :: a -> (# Bool, Bool #) f1 :: a -> (# Bool #) BUT f0 :: a -> b -> (# b #) I think this is stupid. It should be f0 :: a -> (# #) But in fact even that type isn't what you expect (ie the analogue of f :: a -> () ) Here are the kinds of the type constructors: (,,) :: * -> * -> * -> * (,) :: * -> * -> * () :: * (# ,, #) :: * -> * -> * -> # (# , #) :: * -> * -> # BUT (# #) :: * -> # In both respects unboxed unit tuples are behaving differently to boxed ones. This seems bonkers. I propose to fix this, but I wanted to check if anyone is relying on the current odd behaviour. Simon

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