December 2014 - Glasgow-haskell-users

Discovery of source dependencies without --make
by Lars Hupel 13 Dec '15

13 Dec '15

(cross-posted from [haskell-cafe]) Hi, I've got a problem in our – admittedly complex – build process. We're running an automated grading system for student-submitted homework exercises. The compilation proceeds in stages: 1) Compile a library file, marked as trustworthy 2) Compile student submissions using Safe Haskell, able to access a whitelisted set of packages and the previously compiled library files 3) Compile the test suite 4) Link everything together into an executable The invocation is similar to this: ghc -c -outputdir "$OUT" -XTrustworthy Library.hs ghc -c -outputdir "$OUT" -i"$OUT" -XSafe "$SUBMISSION" ghc -c -outputdir "$OUT" -i"$OUT" Test_Suite.hs ghc -outputdir "$OUT" -i"$OUT" -o "$OUT/runner" The second stage works well under the assumption that there's just one single submitted file. If there's more than one, I need to specify them in topological order wrt their module dependencies. Consider two simple modules: A.hs > module A where > > import B > import Library B.hs > module B where Invoking GHC with "A.hs" "B.hs" will fail: A.hs:3:1: Failed to load interface for ‘B’ My naive attempt at solving that problem was to just insert "--make" into the compiler flags. No luck, because according to [1, §4.7.3], "--make" will only look at source files and will ignore the "Library.hi" file from the previous compilation stage. If I give the path to "Library.hs" as well, GHC insists on recompiling it with changed flags ("-XSafe" instead of "-XTrustworthy"). Reading a bit further, I discovered the '-M' flag, however, not only does it output Makefile-formatted output, it also ignores .hi files. Is there any way to get the dependency discovery of '--make' without the rest? I know I could probably make it work if I made a package out of the first build stage, but I really want to avoid that in order to not increase the build complexity even further. Cheers Lars [1] <https://downloads.haskell.org/~ghc/7.6.3/docs/html/users_guide/separate-com…>

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Thread behavior in 7.8.3
by Michael Jones 21 Jan '15

21 Jan '15

I have a general question about thread behavior in 7.8.3 vs 7.6.X I moved from 7.6 to 7.8 and my application behaves very differently. I have three threads, an application thread that plots data with wxhaskell or sends it over a network (depends on settings), a thread doing usb bulk writes, and a thread doing usb bulk reads. Data is moved around with TChan, and TVar is used for coordination. When the application was compiled with 7.6, my stream of usb traffic was smooth. With 7.8, there are lots of delays where nothing seems to be running. These delays are up to 40ms, whereas with 7.6 delays were a 1ms or so. When I add -N2 or -N4, the 7.8 program runs fine. But on 7.6 it runs fine without with -N2/4. The program is compiled -O2 with profiling. The -N2/4 version uses more memory, but in both cases with 7.8 and with 7.6 there is no space leak. I tired to compile and use -ls so I could take a look with threadscope, but the application hangs and writes no data to the file. The CPU fans run wild like it is in an infinite loop. It at least pops an unpainted wxhaskell window, so it got partially running. One of my libraries uses option -fsimpl-tick-factor=200 to get around the compiler. What do I need to know about changes to threading and event logging between 7.6 and 7.8? Is there some general documentation somewhere that might help? I am on Ubuntu 14.04 LTS. I downloaded the 7.8 tool chain tar ball and installed myself, after removing 7.6 with apt-get. Any hints appreciated. Mike

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ANNOUNCE: GHC version 7.8.4
by Austin Seipp 12 Jan '15

12 Jan '15

============================================================== The (Interactive) Glasgow Haskell Compiler -- version 7.8.4 ============================================================== The GHC Team is pleased to announce a new patchlevel release of GHC, 7.8.4. This is an important bugfix release relative to 7.8.3 (with over 30 defects fixed), so we highly recommend upgrading from the previous 7.8 releases. The full release notes are here: https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/release-7-8-… How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: https://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://ghc.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://ghc.haskell.org/trac/ghc/wiki/Platforms http://ghc.haskell.org/trac/ghc/wiki/CodeOwners 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://ghc.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://ghc.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 Hashes & Signatures ~~~~~~~~~~~~~~~~~ On https://downloads.haskell.org/~ghc/7.8.4/ you will find a signed copy of the SHA256 hashes for the tarballs, using my GPG key (keyid 0x3B58D86F). -- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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Changes to the type checker with respect to UndecidableInstances
by Mitsutoshi Aoe 06 Jan '15

06 Jan '15

Hi, I found a difference between GHC 7.6.3 and 7.8.3 with respect to UndecidableInstances. https://gist.github.com/maoe/57a4346eb36aee159916 <https://gist.github.com/maoe/57a4346eb36aee159916> 7.6.3 requires UndecidableInstances to compile this snippet whereas 7.8.3 doesn't. What has changed in the type checker? Mitsutoshi

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ANNOUNCE: GHC 7.10.1 Release Candidate 1
by Austin Seipp 06 Jan '15

06 Jan '15

We are pleased to announce the first release candidate for GHC 7.10.1: https://downloads.haskell.org/~ghc/7.10.1-rc1/ This includes the source tarball and bindists for 64bit/32bit Linux and Windows. Binary builds for other platforms will be available shortly. (CentOS 6.5 binaries are not available at this time like they were for 7.8.x). These binaries and tarballs have an accompanying SHA256SUMS file signed by my GPG key id (0x3B58D86F). We plan to make the 7.10.1 release sometime in February of 2015. We expect another RC to occur during January of 2015. Please test as much as possible; bugs are much cheaper if we find them before the release! -- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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What to do when garbage collector is slow?
by David Spies 05 Jan '15

05 Jan '15

I have a program that, to all appearances, is behaving properly. It uses very little memory to run, it has the profile I would expect looking at +RTS -hc. I have no reason to believe there is a memory leak (in the sense that it's not lazily holding on to things it no longer needs or strictly generating things it doesn't need yet). But it's slow, and according to -sstderr, most of the time is spent garbage-collecting. Why is the garbage-collector consuming so much running time? How can I deal with it? The program is a solution to this problem: https://open.kattis.com/problems/tourist The input data can be found here: http://heim.ifi.uio.no/~db/nm-i-programmering/nm2004/testdata/h.in

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Re: GHC 7.4.2 on Ubuntu Trusty
by Yitzchak Gale 04 Jan '15

04 Jan '15

I wrote: >> This thread makes it clear what a mess >> we have inherited from the days when GHC was primarily a >> research compiler. Let's face it - GHC is now also a serious >> production compiler, and this urgently needs to be cleaned up. hvr wrote: > Are you referring to the GMP dependency or something else? > ...I'm not sure what can be done differently here. Agreed. No, not any one of those many little details. I mean the general extreme difficulty of getting almost any version of GHC working on almost any platform, unless the two were released within a fairly short time of each other. Well, that is, not counting your wonderful ppa for Ubuntu. That is fantastic - but the dire need for it is evidence for the severity of the problem. How about this: Currently, every GHC source distribution requires no later than its own version of GHC for bootstrapping. Going backwards, that chops up the sequence of GHC versions into tiny incompatible pieces - there is no way to start with a working GHC and work backwards to an older version by compiling successively older GHC sources. If instead each GHC could be compiled using at least one subsequent version, the chain would not be broken. I.e., always provide a compatibility flag or some other reasonably simple mechanism that would enable the current GHC to compile the source code of at least the last previous released version. I realize that this might be disruptive to GHC devs, because as a compiler with a research heritage, GHC experiments with its own new features on its own source code. But as a compiler that is used commercially, some general kind of backward portability is critically important. The other direction is equally problematic. Although GHC does support bootstrapping itself from a few previous releases, porting GHC to a new platform has become harder and harder as GHC becomes more complex. I think this could become a threat to the viability of GHC - technology is always changing. As a commercial developer, I am always plagued by nagging worry about GHC portability, forward and backward. Will we always be able in the future to support code we release, or will it die someday because there will no longer exist a GHC able to compile it? Will our whole technology die someday just because we can't get GHC working on a platform we need to support? Thanks, Yitz

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RE: ANNOUNCE: GHC 7.10.1 Release Candidate 1
by Dominic Steinitz 29 Dec '14

29 Dec '14

I counted about 10 people (including me) who appear to be actively keen on it on reddit: http://www.reddit.com/r/haskell/comments/2pnjdk/is_overloadedrecordfields_g…. I would guess there are others. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com On 29 Dec 2014, at 12:00, glasgow-haskell-users-request(a)haskell.org wrote: > > Message: 3 > Date: Mon, 29 Dec 2014 10:29:23 +0000 > From: Simon Peyton Jones <simonpj(a)microsoft.com> > To: Kazu Yamamoto <kazu(a)iij.ad.jp>, "ghc-devs(a)haskell.org" > <ghc-devs(a)haskell.org>, "glasgow-haskell-users(a)haskell.org" > <glasgow-haskell-users(a)haskell.org> > Subject: RE: ANNOUNCE: GHC 7.10.1 Release Candidate 1 > Message-ID: > <618BE556AADD624C9C918AA5D5911BEF5628E269(a)DB3PRD3001MB020.064d.mgd.msft.net> > > Content-Type: text/plain; charset="us-ascii" > > | If I understand correctly, OverloadedRecordFields has not been merged > | yet. Are there any chances to merge it into GHC 7.10.1? > > I'm afraid not. The situation is that Adam has a fairly complete patch for overloaded record fields, but neither he nor I are happy with it. It makes some fairly complicated and pervasive changes, and feels like a sledgehammer to crack a nut. We'd scheduled for Adam to spend a day at MSR for us to work on it together, but Adam had to cancel. We'll hopefully re-arrange. > > Meanwhile it'd be motivating to know who, if anyone, is actively keen on it. Kazu is presumably one. I expect there are others, but I couldn't list them. >

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Re: [Haskell-beginners] ghc prelude home
by Christian Maeder 29 Dec '14

29 Dec '14

23 December 2014 GHC 7.8.4 Released! https://www.haskell.org/ghc/ So 7.8.4 is out! Only the download subpage https://www.haskell.org/ghc/download is not updated yet. Also http://downloads.haskell.org/~ghc/latest/ still refers to http://downloads.haskell.org/~ghc/7.8.3/ (and has a funny 7.8.4 subdirectory). I send this also to glasgow-haskell-users to reach someone who can fix this. Cheers Christian Am 28.12.2014 um 22:28 schrieb Yitzchak Gale: > Yes, sorry, neither 7.8.4 nor 7.10.1 is actually out yet. > They are both release candidates, and will be out soon. > > Thanks, > Yitz > > On Sun, Dec 28, 2014 at 9:50 PM, Antoine Latter <aslatter(a)gmail.com> wrote: >> I don't think GHC 7.10 is out yet: https://www.haskell.org/ghc/download >> >> Although that page doesn't have 7.8.4 on it. > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners >

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Re: ANNOUNCE: GHC 7.10.1 Release Candidate 1
by cg 27 Dec '14

27 Dec '14

> *From:* Austin Seipp <mailto:austin@well-typed.com> > *Sent:* ‎Tuesday‎, ‎December‎ ‎23‎, ‎2014 ‎15‎:‎36 > *To:* ghc-devs(a)haskell.org <mailto:ghc-devs@haskell.org>, > glasgow-haskell-users(a)haskell.org <mailto:glasgow-haskell-users@haskell.org> > > We are pleased to announce the first release candidate for GHC 7.10.1: > > https://downloads.haskell.org/~ghc/7.10.1-rc1/ > Besides downloading a tarball, can I checkout it using git? I tried using sync-all as described on wiki [1] to checkout it: ./sync-all checkout ghc-7.10 but it seems it doesn't work, there are error message like: error: pathspec 'ghc-7.10' did not match any file(s) known to git. [1] https://ghc.haskell.org/trac/ghc/wiki/WorkingConventions/Releases

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