January 2015 - 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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ANNOUNCE: GHC 7.10.1 Release Candidate 2
by Austin Seipp 21 Feb '15

21 Feb '15

We are pleased to announce the second release candidate for GHC 7.10.1: https://downloads.haskell.org/~ghc/7.10.1-rc2/ 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. 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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Restricted Template Haskell
by Greg Weber 03 Feb '15

03 Feb '15

Hello GHC friends! I am starting up a proposal for variants of Template Haskell that restrict what operations are available. The goal is to make TH easier for users to reason about and to allow for an easier compilation story. Here is the proposal page: https://ghc.haskell.org/trac/ghc/wiki/TemplateHaskell/Restricted Right now the proposal does not have any details and the goal is to write out a clear specification. If this sounds interesting to you, let me know or leave some feedback on the wiki. Thanks, Greg Weber

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ANN: deepseq-bounded 0.5 -> 0.6
by Andrew Seniuk 25 Jan '15

25 Jan '15

This may affect depending code. Please consult the distro changelog for specific information about how your code might be affected, or better yet, refer to http://www.fremissant.net/deepseq-bounded/transition-5-6-7.html and http://www.fremissant.net/deepseq-bounded/grammar.html This is a transitional version of deepseq-bounded, with stability of the grammar expected in early March for version 0.7. This also causes major version bumps to the seqaid and leaky packages. To update everything, issue cabal update cabal install --reinstall --force-reinstalls seqaid which reinstalls the latest deepseq-bounded in passing. And also if you were to run "seqaid demo" it will use the updated version of leaky, so everything's up to date. The homepage for these projects starts at http://www.fremissant.net/deepseq-bounded-seqaid-leaky.html Kind Regards, Andrew

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Unable to build 7.10.1 RC1 on Jessie
by harry 25 Jan '15

25 Jan '15

I'm trying to build 7.10.1 RC on Debian Jessie. I get an error: configure: error: in `/ghc-7.10.0.20141222/libffi/build/x86_64-unknown-linux-gnu': configure: error: C++ preprocessor "/lib/cpp" fails sanity check config.log shows: configure: failed program was: | /* confdefs.h */ | #define PACKAGE_NAME "libffi" | #define PACKAGE_TARNAME "libffi" | #define PACKAGE_VERSION "3.1" | #define PACKAGE_STRING "libffi 3.1" | #define PACKAGE_BUGREPORT "http://github.com/atgreen/libffi/issues" | #define PACKAGE_URL "" | #define PACKAGE "libffi" | #define VERSION "3.1" | #define STDC_HEADERS 1 | #define HAVE_SYS_TYPES_H 1 | #define HAVE_SYS_STAT_H 1 | #define HAVE_STDLIB_H 1 | #define HAVE_STRING_H 1 | #define HAVE_MEMORY_H 1 | #define HAVE_STRINGS_H 1 | #define HAVE_INTTYPES_H 1 | #define HAVE_STDINT_H 1 | #define HAVE_UNISTD_H 1 | #define HAVE_DLFCN_H 1 | #define LT_OBJDIR ".libs/" | /* end confdefs.h. */ | #ifdef __STDC__ | # include <limits.h> | #else | # include <assert.h> | #endif | Syntax error configure:12860: error: in `/ghc-7.10.0.20141222/libffi/build/x86_64-unknown-linux-gnu': configure:12862: error: C++ preprocessor "/lib/cpp" fails sanity check This can be reproduced by running the following commands in the debian:jessie docker image: apt-get update apt-get install ncurses-dev curl gcc ghc make libgmp-dev xz-utils curl http://downloads.haskell.org/~ghc/7.10.1-rc1/ghc-7.10.0.20141222-src.tar.xz | tar xJ cd ghc-* ./configure make Any suggestions for someone who knows nothing about c or cpp? -- View this message in context: http://haskell.1045720.n5.nabble.com/Unable-to-build-7-10-1-RC1-on-Jessie-t… Sent from the Haskell - Glasgow-haskell-users mailing list archive at Nabble.com.

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template haskell vs. -prof
by Evan Laforge 24 Jan '15

24 Jan '15

I ran into trouble compiling template haskell with -prof, and came across the ghc manual "7.9.4. Using Template Haskell with Profiling". Unfortunately I can't use its advice directly since I put profiling and non-profiling .o files into different directories. But in principle it seems it should work, I just have to get ghc to load TH from the debug build directory, which is built with -dynamic, while continuing to load from the profile build directory. But are there flags to get it to do that? I'm using "-osuf .hs.o -ibuild/profile/obj". If I put ":build/debug/obj" on the -i line, it still seems to find the profiling one. The ghc manual advice probably gets around it by using different -osufs... I guess TH somehow ignores -osuf? Except when I compile the debug version with osuf, if finds them fine, so I don't really know how it works. Is there a way I can directly tell TH where to look? It seems awkward to rely on all these implicit and seemingly undocumented heuristics. And, this is somewhat beside the point, but shouldn't TH theoretically be able to load directly from .hs and compile to bytecode like ghci can do if it doesn't find the .o file? And, even more beside the point, the only reason I'm messing with TH is for a really simple (one line) multi-line string literal quasiquote. Surely I'm not the only person who would enjoy a -XMultiLineStringLiteral extension? The alternative seems to be a program to add or strip all of the "\n\"s, and when I want to edit, copy out, strip, edit, paste back in, add back. At that point maybe it's easier to just get used to all the \s... but then indentation is all a bit off due to the leading \.

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Fwd: UNPACK Existential datatype
by Nicholas Clarke 23 Jan '15

23 Jan '15

I'd like to be able to use the UNPACK pragma on an existentially quantified datatype. So as in the below example: {-# LANGUAGE ExistentialQuantification #-} data Foo = forall a. Show a => Foo !a instance Show Foo where show (Foo a) = "Foo! " ++ show a data Bar = Bar {-# UNPACK #-} !Foo deriving (Show) main :: IO () main = do let foo = Foo "Hello" bar = Bar foo print bar I would expect the `Foo` constructor to be unpacked into Bar, as if I had written: data Bar = forall a. Show a => Bar !a However, instead I get the 'Ignoring unusable UNPACK pragma on the first argument of ‘Bar’' warning. Is there a reason this shouldn't work, or a workaround to get it to do so? Cheers, Nick

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How to remove a cabal package from the local system?
by Volker Wysk 23 Jan '15

23 Jan '15

Hi! I have installed/registered a new version of a package with cabal by accident. How can I remove it again? There is something in ~/.cabal/packages/hackage.haskell.org, but the defective version isn't included. bye V.W.

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ANN: git-monitor
by John Wiegley 22 Jan '15

22 Jan '15

git-monitor auto-commits all changes to a Git working tree, within a special branch named "refs/snapshots/refs/heads/<branch>". It has no impact on the Git repository otherwise, and will not effect your real branches. It has the following features: - It is designed to be extremely resource efficient, both in CPU cost and memory. I wanted something I could run several instances of on my laptop, without paying much of a battery cost. This efficiency is achieved by using gitlib with the libgit2 backend. The current state of the working tree is maintained as a Git object in memory, and is updated in place before being written back out to disk. Thus, the amount of computation done remains minimal, as we do not need to rebuild the Git tree at each iteration (as "git-commit" would do). - Whenever git-monitor is exited and restarted, the previous snapshot "branch" is discarded. These are only intended to be viable during and between runs. - By having such a branch, you can easily browse through the diffs of your changes throughout the day. By default, every action taken is printed to the console where git-monitor is run, but it can also be run in silent mode, for example if you choose to background it for the rest of the day. http://hackage.haskell.org/package/git-monitor https://github.com/jwiegley/git-monitor Please report issues to the GitHub page. I have been using git-monitor on a regular basis for more than a year now, so I felt it finally deserved an announcement here. Thank you, John Wiegley (johnw on IRC/freenode)

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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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