April 2014 - ghc-devs

old-time.git/tests/time004.hs is DST-sensitive :-/
by Herbert Valerio Riedel 26 Oct '14

26 Oct '14

Hi *, if anyone wonders, why TEST=time004 suddenly fails: it's sensitive to DST (and depends on your system's TZ-config): http://git.haskell.org/packages/old-time.git/blob/HEAD:/tests/time004.hs For me, the comparison this unit-test checks now suddenly fails, because the DST-switch occurs on different days in 2012 and 2013 in my TZ, i.e. length "Sun Oct 27 10:56:42 CET 2013" /= length "Sat Oct 27 11:56:42 CEST 2012" Does anyone happen to know what the rationale behind this 'time004' unit test was? Cheers, hvr

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FFI: c/c++ struct on stack as an argument or return value
by Yuras Shumovich 07 Oct '14

07 Oct '14

Hi, Right now ghc's FFI doesn't support c/c++ structures. Whenever we have foreign function that accepts or returns struct by value, we have to create wrapper that accepts or returns pointer to struct. It is inconvenient, but actually not a big deal. But there is no easy workaround when you want to export haskell function to use it with c/c++ API that requires structures to be passed by value (Usually it is a callback in c/c++ API. You can't change it's signature, and if it doesn't provide some kind of "void* userdata", then you are stuck.) I'm interested in fixing that. I'm going to start with 'foreign import "wrapper" ...' stuff. Calling conventions for passing c/c++ structures by value are pretty tricky and platform/compiler specific. So initially I'll use libffi for that (it will work when USE_LIBFFI_FOR_ADJUSTORS is defined, see rts/Adjustor.c). It will allow me to explore design space without bothering about low level implementation details. Later it could be implemented for native (non-libffi) adjustors. Is anybody interested it that? I appreciate any comments/ideas. Right now I don't have clear design. It would be nice to support plain haskell data types that are 1) not recursive, 2) has one constructor and 3) contains only c/c++ types. But it doesn't work with c/c++ unions. Any ideas are welcome. An example how to use libffi with structures: http://www.atmark-techno.com/~yashi/libffi.html#Structures Thanks, Yuras

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Extending fold/build fusion
by Akio Takano 05 Sep '14

05 Sep '14

Hi, I have been thinking about how foldl' can be turned into a good consumer, and I came up with something that I thought would work. So I'd like to ask for opinions from the ghc devs: if this idea looks good, if it is a known bad idea, if there is a better way to do it, etc. The main idea is to have an extended version of foldr: -- | A mapping between @a@ and @b@. data Wrap a b = Wrap (a -> b) (b -> a) foldrW :: (forall e. Wrap (f e) (e -> b -> b)) -> (a -> b -> b) -> b -> [a] -> b foldrW (Wrap wrap unwrap) f z0 list0 = wrap go list0 z0 where go = unwrap $ \list z' -> case list of [] -> z' x:xs -> f x $ wrap go xs z' This allows the user to apply an arbitrary "worker-wrapper" transformation to the loop. Using this, foldl' can be defined as newtype Simple b e = Simple { runSimple :: e -> b -> b } foldl' :: (b -> a -> b) -> b -> [a] -> b foldl' f initial xs = foldrW (Wrap wrap unwrap) g id xs initial where wrap (Simple s) e k a = k $ s e a unwrap u = Simple $ \e -> u e id g x next acc = next $! f acc x The wrap and unwrap functions here ensure that foldl' gets compiled into a loop that returns a value of 'b', rather than a function 'b -> b', effectively un-CPS-transforming the loop. I put preliminary code and some more explanation on Github: https://github.com/takano-akio/ww-fusion Thank you, Takano Akio

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Can't install 32-bit ghc-7.8.1 on 64-bit xubuntu 14.04
by kyra 30 Aug '14

30 Aug '14

Hi, I have unpacked ghc-7.8.1-i386-unknown-linux-deb7.tar.xz to ~/data/Work/ghc-7.8.1-i386. Now I have the following: awson@awsonvirt:~/data/Work/ghc-7.8.1-i386$ ./configure --prefix=/home/awson/data/ghc-7.8.1-i386 checking for path to top of build tree... utils/ghc-pwd/dist-install/build/tmp/ghc-pwd-bindist: line 3: /home/awson/data/Work/ghc-7.8.1-i386/utils/ghc-pwd/dist-install/build/tmp/ghc-pwd: No such file or directory configure: error: cannot determine current directory ghc-pwd is definitely there but it does not start it seems. Perhaps, the system lacks some shared libs or something. There absolutely no problems with 64-bit ghc. Regards, Kyra

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7.8.1 plan
by Austin Seipp 16 Jul '14

16 Jul '14

Hello all, As I'm sure you're all aware, it's the final countdown. The (final) source distribution will be up within a few hours, and then we'll continue on from there. Yay! I will post an update when that is, so Gabor/Luke/Karel can make binaries from the sources as I do so. Second, there are just two things I want to note: - For people following the Windows debacle in #8834, there has been a bug fixed, but one may still remain. The TL;DR of this is that we currently have a committed workaround in place we'll keep using, but Simon has made some good steps towards finding the bug. - Lots of people, I'm sure, are wondering what's going on with Safe Haskell and the GND story. The TL;DR of this one is that "everything will be the same as in 7.6" - GND is considered an Unsafe feature, and Data.Coerce is behind Unsafe bars. From a safety point of view, nothing should change for library authors I cherry picked these changes into 7.8 last night. In the mean time, the 7.8 branch is effectively closed. If you have something to commit, and I *really* mean something, you can let me know. But your deadline is hours, not days! I'm doing a final review of all the trees before pushing the library tags, and after that I'll begin rolling the sdist. Anyway, the time is finally here, so let's get it over with! -- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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Proposal: Partial Type Signatures
by Thomas Winant 19 Jun '14

19 Jun '14

Dear GHC developers, Together with Tom Schrijvers, Frank Piessens and Dominique Devriese, I have been working on a proposal for adding *Partial Type Signatures* to GHC. In a partial type signature, annotated types can be mixed with inferred types. A type signature is written like before, but can now contain wildcards, written as underscores. The types of these wildcards or unknown types will be inferred by the type checker, e.g. foo :: _ -> Bool foo x = not x -- Inferred: Bool -> Boo The proposal also includes a form of generalisation which aligns with the existing generalisation that GHC does. We have written down a motivation (when and how might you use this) and details about the design and implementation on the following wiki page: https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures We have a (work in progress) implementation [1] of the feature based on GHC. It currently implements most of what we propose, but there are some remaining important bugs mostly concerning the generalisation. We also described our design and presented a formalisation based on the OutsideIn(X) formalism in a paper [2] presented at PADL'14. What we are hoping to get from the people on this list is any of the below: * Read the design, play with the implementation and tell us any comments you may have about the feature, its design and implementation. * Opinions on whether this feature might be acceptable in GHC upstream at some point (if not, we do not think it's worth developing the implementation much further). * Perhaps a code review or a discussion with someone more knowledgeable about the internals of GHC's type checker about how we might fix the remaining problems in our implementation (specifically, we could use some help with implementing the generalisation of partial type signatures). * Feedback on the `Questions and issues' section on the wiki page. Kind regards, Thomas Winant [1]: https://github.com/mrBliss/ghc-head/ [2]: https://lirias.kuleuven.be/bitstream/123456789/423475/3/paper.pdf Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

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Offering GHC builder build slaves
by Alain O'Dea 18 Jun '14

18 Jun '14

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi folks: I have successfully built Ian Lynagh's GHC builder on Ubuntu and SmartOS and I would like to offer build slaves based on Carter's mirroring of the code to https://github.com/cartazio/ghc-builder. I can offer several build slaves, but I'm not sure what the process is. How do I run multiple build slaves? Do I need a separate username for each? Is there a username convention? The suggestion at https://ghc.haskell.org/trac/ghc/wiki/Builder is that I post a username and password to ghc@. There are two issues with this: 1. ghc@ does not exist as far as I can tell 2. Posting a password to a mailing list will make it publicly accessible and allow others to impersonate my build slaves I am happy to send this information if the admins of the GHC builder infrastructure are comfortable with the risks. Alternatively, I am able to send this via GPG encrypted email given the public key and email of an admin. Feel free to contact me on or off list about this. Best, Alain -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.14 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJTQ0uTAAoJEP0rIXJNjNSA+fMH/2p9yeWgpfDeaTHilur5qoZ6 6DZiktJgvMpVeqFwHyaFMk+ubEp8/xU/VUrOEztr01jmzNLS2UoqDVH/7EZPZPtV 0ONh/bcYYA8EBa9SCqaVXVb9I8EdDE6w2cQGDqnwHqaFerAUqv8OiQEWyJCuJSdr 7EL/vcacNfr5Ix4oG2pkESvEJBHHEN4ZTXoKeJnyQT93o2RaC1fgImm6F6tgpdQE Jh+QInIX1dRuSl+pDlHg6kbLZqFG8Mnyz0bcWuUL2ekGQBp3HtT0MwonM9HUTmmG 0baRYUaK/moO5Q6lUXhI2eRT/UFl4qnzwJw/sIVuaL7h1Ikj0ZMOuPs0GjfRbY8= =/Rwk -----END PGP SIGNATURE-----

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Re: Offering GHC builder build slaves
by Páli Gábor János 07 Jun '14

07 Jun '14

2014-04-09 0:25 GMT+02:00 Lyndon Nerenberg <lyndon(a)orthanc.ca>: > Is there any way to verify that builder-client can actually do a successful build, > without having access to the build system server? 'builder-client --do-build' > wants to connect and authenticate first; it would be helpful if there was a way > to bypass that so that I can first verify the local build environment is sane. This is because the builder client gets the commands to be executed from the server. A naive solution would be to put the commands in the script and run it. You can find the current set of installed commands at one of the active builders page, e.g. [1]. Note that you may have to change some of them, such as the flags passed to configure script and name of the make(1) command. [1] http://haskell.inf.elte.hu/builders/solaris-x86-head/23.html

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GHC status report
by Simon Peyton Jones 09 May '14

09 May '14

As Austin has told us, there's a draft of the GHC Status Report for the HCAR, here: https://ghc.haskell.org/trac/ghc/wiki/Status/May14 Have we missed out something you have been working hard on? Do take a moment to add a bullet in an appropriate place (it's a wiki). I'd like to be sure that we are giving credit to all the appropriate people, so please help us fix that too. GHC is a team effort. Deadline is 1 May I think. Thanks Simon

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Automating Windows setup for development
by Niklas Larsson 06 May '14

06 May '14

Hi! I have made a Powershell script that sets up a GHC build environment on Windows from scratch. It's at https://github.com/melted/getghc. It largely follows the instructions at https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows/MSYS2. It has no dependencies aside from Powershell 3.0. The reason I made it was to make it easier to set up a build bot on a clean machine. But it's probably generally useful for people who want to develop GHC on Windows. Usage: - Put the script in an empty directory - Run it - Hope for the best Potential problems: - If Python 2.7 is already installed and not on the path, the script wont install it, and msys wont pick up the path. Solution: Add the path to python in the control panel. - Powershell wont run unsigned scripts by default. The error message will give a hint how to disable that. I will add a signed version as soon as I can figure out how. Niklas

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