April 2010 - Glasgow-haskell-users

index*OffAddr
by Roman Leshchinskiy 23 Apr '10

23 Apr '10

In package vector, primitive vectors (the ones that Data.Vector.Unboxed is built on top of) are represented as follows (ByteArray and friends are wrappers for various GHC primitives provided by package primitive): data Vector a = Vector Int -- offset into the ByteArray Int -- length ByteArray -- data This representation supports cheap slicing which is quite crucial. However, indexing into such vectors is a bit more expensive than necessary: index (Vector i _ arr) j = indexByteArray arr (i+j) Ultimately, this requires 2 additions to get the element's address: <base address off the ByteArray> + ((i + j) * <size of element>) I'd like to always allocate pinned ByteArrays and store the starting address of the vector instead of the offset: data Vector a = Vector Addr Int ByteArray This would make indexing cheaper as it would require only one addition: index (Vector addr i _) = indexOffAddr addr i This is quite a big deal if indexing happens in an inner loop (some algorithms become up to 20% faster). Of course, the backend could optimise the offset-based version by performing partial redundancy elimination but it doesn't and it probably wouldn't get all interesting cases even if it did. So the second version is better. The problem is that I can't implement it because I must touch the ByteArray after accessing the memory. This results in code like this which hides the constructor, breaking various optimisations: case indexIntOffAddr# addr# i# of { n# -> case touch# arr# realWorld# of { _ -> I# n# }} After thinking about this for a while, I came up with two possible solutions. One is to provide a "pure" version of touch#: use# :: o -> o' -> o' such that use# x y = y. This would change the code above to: I# (use# arr# (indexIntOffAddr# addr# i#)) I don't know how to implement this, though, because use# would have to be able to return arbitrary (unboxed) types and the code generator doesn't really seem to support this. A perhaps simpler solution is to add a new set of primitives: indexIntOffAddrUsing# :: o -> Addr# -> Int# -> Int# ... These would take an additional argument which they'd touch and otherwise ignore. The code would then become: I# (indexIntOffAddrUsing# arr# addr# i#) Incidentally, the index*OffAddr# primitives don't seem to be used anywhere. Any thoughts? Roman

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GHC version 6.12.2 - testsuite results
by Jens Petersen 23 Apr '10

23 Apr '10

Hi, FYI I just ran the full testsuite (my first time) on a fedora devel build for Fedora 14 and got the following results: * i686 (all) OVERALL SUMMARY for test run started at gum agd 23 7:20:47 saaku UTC 2010 2375 total tests, which gave rise to 13152 test cases, of which 0 caused framework failures 2787 were skipped 10016 expected passes 322 expected failures 1 unexpected passes 26 unexpected failures Unexpected passes: length001(ghci) Unexpected failures: CPUTime001(optasm,threaded2) T1969(normal) T2486(optc) T3245(optc,profc) T3286(optc,profc) arith008(optc) arr016(optc) arr017(optc) arrowrun002(optc,profc) cgrun034(optc) cholewo-eval(optc,profc) concprog001(ghci) fast2haskell(optc,profc) ffi009(optc,profc) fun_insts(optc,profc) numrun012(optc,profc) signals002(threaded2) since it takes a while to run I thought I would report the results here for the record. :) * x86_64 (all) OVERALL SUMMARY for test run started at gum agd 23 7:38:09 saaku UTC 2010 2375 total tests, which gave rise to 13152 test cases, of which 0 caused framework failures 2772 were skipped 10057 expected passes 321 expected failures 0 unexpected passes 2 unexpected failures Unexpected failures: T3245(threaded2) concprog001(ghci) For full details see: http://koji.fedoraproject.org/koji/taskinfo?taskID=2133402 I am guessing the testsuite is run more on 64bit Linux. :) Thank you, Jens ps With "make fast" on Fedora 13 I got just: * i686 (fast) OVERALL SUMMARY for test run started at gum agd 23 9:09:38 saaku UTC 2010 2375 total tests, which gave rise to 13147 test cases, of which 0 caused framework failures 11024 were skipped 2062 expected passes 59 expected failures 0 unexpected passes 2 unexpected failures Unexpected failures: T1969(normal) T2486(optc) For 64bit there were no unexpected fast results. :) See http://koji.fedoraproject.org/koji/taskinfo?taskID=2133525

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-K in 6.12.2
by Serge D. Mechveliani 23 Apr '10

23 Apr '10

Dear GHC developers, I am trying ghc-6.12.2 on Debian Linux, i386-family, on the DoCon test. There is a difference in memory management, with respect to 6.12.1. For the test compiled under -O, 2300k in "./Main +RTS -K2300k -RTS" is the minimal memory option of this kind for the test to finish without break. In 6.12.2, 90k is sufficient, maybe, GHC ignores this "-K", -"M" ... Could you explain, please? Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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Unicode alternative for '..' (ticket #3894)
by Roel van Dijk 21 Apr '10

21 Apr '10

I'm a big fan of the UnicodeSyntax [1] language extension. But I don't particularly like the alternative for the ellipsis '..'. I'm not sure if it was a conscious choice or a mistake to use the '⋯' character. I haven't really encountered that symbol before except for matrices and the like [2]. Therefore I propose to change the character from '⋯' to '…'. I submitted a bug report for this a few weeks ago [3]. Today I attached a patch which implements this change. Here are 4 code snippets for comparison: -- Simple ASCII import Data.Bool ( Bool(..) ) f :: [Int] f = [1, 3 .. 10] ++ [10..100] -- Current situation (MIDLINE HORIZONTAL ELLIPSIS, U+22EF) import Data.Bool ( Bool(⋯) ) f ∷ [Int] f = [1, 3 ⋯ 10] ++ [10⋯100] -- Proposed change (HORIZONTAL ELLIPSIS, U+2026) import Data.Bool ( Bool(…) ) f ∷ [Int] f = [1, 3 … 10] ++ [10…100] -- Another alternative (TWO DOT LEADER, U+2025) import Data.Bool ( Bool(‥) ) f ∷ [Int] f = [1, 3 ‥ 10] ++ [10‥100] The TWO DOT LEADER also looks nice, but I think we must consider more than looks alone (which is a matter of fonts) and take the semantics into account. I would really like some feedback on this since it is a change that breaks backwards compatibility (even though it is a really small change). Regards, Roel van Dijk 1 - http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#u… 2 - http://en.wikipedia.org/wiki/Ellipsis#In_mathematical_notation 3 - http://hackage.haskell.org/trac/ghc/ticket/3894

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Output character encoding for ghc on OpenBSD
by Matthias Kilian 19 Apr '10

19 Apr '10

Hi, as some of you may know, I'm working on an update of OpenBSDs ghc port to 6.12.2, currently chasing down the last remaining testsuite failures. Yesterday, I ran into a problem which I have a fix for, but only a really ugly fix, and I need some opinions of what users would prefer. The problem is that Haskell uses unicode characters internally (ghc itself uses UTF-32 internally, where the endianess depends on the architecture it's running on), and that any Haskell program (including ghc and ghci) has to convert between the internal representation and the actual locale settings of the system it's running on. Unfortunately, OpenBSD is really bad if it comes to locale support; the only supported locales are the C and the POSIX locales, so even if you set LC_ALL or LC_CTYPE to something like, for example, de_DE.iso88591, this would have no effect on OpenBSD. Anyway, the short story is that I have to either hard-code the character set to something like utf-8, or ghc will start to behave really strange (for example, ghci would terminate immediately if you just *type* a non-ASCII character). So what would you prefer? - Use utf-8 and only utf-8 (i.e. hardcoded)? - Use something like iso-8859-15 (hardcoded)? - Make it configurable via some non-standard environment variable (GHC_CODESET, for example). If so, what should be the default if the environment variable isn't set? Back to 7 bit (ASCII)? utf-8? Some of the latin variants? Your suggestions are appreciated. Thanks in advance. Ciao, Kili

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Encountered absent arg
by Louis Wasserman 19 Apr '10

19 Apr '10

Yo, I didn't find many references to this on Google except a 2001 message saying "Send this problem to us!" I don't know what's changed since then, so I'll poke the list: I compiled my code with -fdicts-strict. (Why is this not a mainstream thing? It eliminates gratuitous polymorphism overhead, which is one of my biggest sources of angst!) Looking at ghc-core, my code appears to *always* give the exception "Oops! Entered absent arg ww_s9eC{v} [lid] <pred>main:Data.Algebra.Ring.Ring{tc r2tU} c{tv a8Os} [tv]" Is this typical? Where should I send this? Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

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"ld" memory usage
by Roman Beslik 18 Apr '10

18 Apr '10

Hi. This is not strictly a GHC question. I observed that "ld" when linking GHC-compiled programs eats 0.5 GB of resident memory. ~3 times more than GHC or Haddock. So if there is not enough free memory "ld" uses virtual memory and works very slowly (practically does not use CPU). I'd like to know, is anyone interested in researching and improving memory usage? Is it "ld" or GHC problem? I found a similar discussion here http://article.gmane.org/gmane.comp.lang.haskell.cafe/66189 but it was too broad and went nowhere. -- Best regards, Roman Beslik.

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Literate files in the GHC source
by Tyson Whitehead 17 Apr '10

17 Apr '10

I'm just wondering how exactly are the literate files in the GHC source suppose to be treated. I would like to read some of the documentation. The presence of various latex commands such as subsection strongly suggests they are done in latex. Running pdflatex, however, doesn't work. Nor does created a wrapper latex file to define the document class, the code environment, etc., as it then bombs out on such things as non-escaped '#'s. I searched around on the Internet and mailing list archives didn't seem to find anything. If I had to guess, I would suspect it started as actually latex documentation, but has fallen into a state of disrepair. Is this correct? Thanks! -Tyson

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Re: Can't install Criterion package on ghc ..
by John Lato 17 Apr '10

17 Apr '10

> From: Mozhgan kabiri <mozhgan.kabiri(a)gmail.com> > > Hi, > > I am trying to install Criterion package, but I keep getting an error and I > can't figure it out why it is like this !! > > mozhgan@Mozhgan-KCh:~$ cabal install Criterion > Resolving dependencies... > Configuring vector-algorithms-0.3... > Preprocessing library vector-algorithms-0.3... > Building vector-algorithms-0.3... ... > [8 of 9] Compiling Data.Vector.Algorithms.Intro ( > Data/Vector/Algorithms/Intro.hs, dist/build/Data/Vector/Algorithms/Intro.o ) > ghc: panic! (the 'impossible' happened) > (GHC version 6.10.4 for i386-unknown-linux): > idInfo co{v a9WB} [tv] This is definitely a bug in GHC, most likely related to type families and fixed in GHC-6.12.x If you can upgrade to ghc-6.12.1, that should solve this problem. If you need to remain on ghc-6.10.4, try installing an older version of criterion. You can do this with 'cabal install criterion-0.4.1.0' Criterion-0.5 is the first version to depend upon vector-algorithms, so any previous version has a chance of working. John

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Using -fext-core without a Main function
by Hal Daume III 16 Apr '10

16 Apr '10

If I have a file 'Foo.hs' that contains one line 'addOne x = x + 1', I want to run something like: ghc -c -fext-core Foo.hs to get the core version of this file. Unfortunately, when I do that, it complains that Main doesn't have a function main. And it doesn't produce the .hcr file. I tried adding -no-hs-main but that doesn't help. I can add 'main = undefined' to Foo.hs, but then the core file doesn't contain the declaration of addOne because it's not used. Any suggestions? Thanks! -h -- Hal Daume III --- me AT hal3 DOT name | http://www DOT hal3 DOT name "Arrest this man, he talks in maths." | http://nlpers.blogspot.com

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