July 2012 - Haskell-Cafe

COBOL-85 parser, anyone?
by Richard O'Keefe 20 Jul '12

20 Jul '12

Does anyone have a parser for COBOL-85 written in Haskell, or written using some freely available tool that communicates easily with Haskell? I don't need it _yet_, but I'm talking with someone who is trying to get access to a real legacy site with a bunch of, well, basically COBOL 85, but there are extensions... We're not talking about transformation at this stage, just analysis. I could probably hack up the extensions given a place to start. I've found some papers and more dead links than I care for and lots of mention of ASF+SDF which is apparently superseded by Rascal.

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Bug or feature?
by Miguel Mitrofanov 20 Jul '12

20 Jul '12

Hi cafe! I'm a bit confused by the DefaultSignatures extension. It's unclear whether to consider the following an example of clever use of this extension, or an example of abuse of it: {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE DefaultSignatures #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} module SubClass where import GHC.Prim(Constraint) data Void (c :: * -> Constraint) = Void data Evidence c a where Evidence :: c a => Evidence c a class c1 :<= c2 where isSubClass :: c1 a => Void c1 -> Evidence c2 a default isSubClass :: c2 a => Void c1 -> Evidence c2 a isSubClass Void = Evidence instance Show :<= Show instance Floating :<= Fractional instance Real :<= Num -- instance Fractional :<= Floating -- NO ROTTEN WAY {- Examples -} data Wrapper c where Wrapper :: c a => a -> Wrapper c instance (c :<= Show) => Show (Wrapper c) where show (Wrapper (a :: t)) = case isSubClass (Void :: Void c) :: Evidence Show t of Evidence -> show a absWrap :: (c :<= Num) => Wrapper c -> Wrapper c absWrap (Wrapper (a :: t) :: Wrapper c) = case isSubClass (Void :: Void c) :: Evidence Num t of Evidence -> Wrapper (abs a) What do you think? Also, it's a bit strange that the first example (instance (c :<= Show) => Show (Wrapper c)) requires UndecidableInstances, while the second one (absWrap) requires FlexibleContexts - although being remarkably similar.

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How to add constraint to .cabal?
by Magicloud Magiclouds 19 Jul '12

19 Jul '12

Hi, Say I have a package that only appends --constraint="template-haskell==2.7.0.0" --constraint="warp-tls==1.2.1" could I install it. Now I want to release the package, then how could I have these constraint into the .cabal so the user would not get troubled? -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Re: [Haskell-cafe] Fwd: hackage compile failure with QuickCheck 2.5
by Alexander Foremny 19 Jul '12

19 Jul '12

Dear Levent, unfortunately I am at a loss here. As far as I understand it this should be fixed in QuickCheck's .cabal file or on Hackage. But I am not experienced enough to decide. You best wait for someone else to comment on this. Depending on template-haskell in your .cabal file is not the way to go as far as I understand it. But maybe it's a possible work-around in case you depend on the package being available on Hackage timely. Regards, Alexander Foremny 2012/7/17 Levent Erkok <erkokl(a)gmail.com>: > It builds fine locally on my box; but not on hackage. Here's the page: > http://hackage.haskell.org/package/sbv-2.2 > > Thanks for looking into this Alexander, I appreciate your help. > > -Levent. > > > On Tue, Jul 17, 2012 at 9:09 AM, Alexander Foremny > <alexanderforemny(a)gmail.com> wrote: >> >> Which package are you trying to build? Is it a local package that >> fails to build or something on Hackage? Its .cabal file or at least >> full dependencies would be of interest. >> >> Regards, >> Alexander Foremny >> >> 2012/7/17 Levent Erkok <erkokl(a)gmail.com>: >> > Thanks Alexander. However, I'm not sure how to use the workaround >> > described >> > so I can get hackage to properly compile my package. It sounds like I >> > have >> > to add a "template-haskell >= 2.7.0.0" dependency to my own cabal file, >> > which sounds like the wrong thing to do in the long-run. >> > >> > Is there something that can be done on the hackage/ghc side to avoid >> > this >> > issue? Or something less drastic than adding a template-haskell >> > dependency >> > on my own package's cabal file? >> > >> > Thanks, >> > >> > -Levent. >> > >> > >> > On Tue, Jul 17, 2012 at 7:31 AM, Alexander Foremny >> > <alexanderforemny(a)gmail.com> wrote: >> >> >> >> Dear Levent, >> >> >> >> I think this [1] could be related. >> >> >> >> Regards, >> >> Alexander Foremny >> >> >> >> PS. Sent this to Levent directly. Here's a copy for the mailing list. >> >> Sorry for the noise. >> >> >> >> [1] >> >> >> >> http://haskell.1045720.n5.nabble.com/Bad-interface-problem-td5714184.html >> >> >> >> ---------- Forwarded message ---------- >> >> From: Alexander Foremny <alexanderforemny(a)gmail.com> >> >> Date: 2012/7/17 >> >> Subject: Re: [Haskell-cafe] hackage compile failure with QuickCheck 2.5 >> >> To: Levent Erkok <erkokl(a)gmail.com> >> >> >> >> >> >> Dear Levent, >> >> >> >> I think this [1] could be related. >> >> >> >> Regards, >> >> Alexander Foremny >> >> >> >> [1] >> >> >> >> http://haskell.1045720.n5.nabble.com/Bad-interface-problem-td5714184.html >> >> >> >> 2012/7/17 Levent Erkok <erkokl(a)gmail.com>: >> >> > [This message is more appropriate for a hackage mailing list I >> >> > presume, >> >> > but >> >> > that doesn't seem to exist. Let me know if there's a better place to >> >> > send >> >> > it.] >> >> > >> >> > I'm having a hackage compile failure for a newly uplodaded package >> >> > that >> >> > has >> >> > a QuickCheck 2.5 dependence. The error message is: >> >> > >> >> > [13 of 13] Compiling Test.QuickCheck.All ( Test/QuickCheck/All.hs, >> >> > dist/build/Test/QuickCheck/All.o ) >> >> > >> >> > Test/QuickCheck/All.hs:15:1: >> >> > Bad interface file: >> >> > >> >> > >> >> > /usr/local/tmp/archive/install/lib/template-haskell-2.6.0.0/ghc-7.4.1/Language/Haskell/TH.hi >> >> > Something is amiss; requested module >> >> > template-haskell-2.6.0.0:Language.Haskell.TH differs from name found >> >> > in >> >> > the >> >> > interface file template-haskell:Language.Haskell.TH >> >> > >> >> > >> >> > The full log file is at (search for "Something is a miss" in it): >> >> > >> >> > http://hackage.haskell.org/packages/archive/sbv/2.2/logs/failure/ghc-7.4 >> >> > >> >> > Needless to say, I don't see this problem when I compile this package >> >> > at >> >> > home with the same compiler (ghc 7.4.1) as hackage is using; also >> >> > Hackage >> >> > has a successfully compiled QuickCheck 2.5 package. >> >> > >> >> > Could it be something related to the particular cabal/ghc >> >> > installation >> >> > on >> >> > the hackage server? In particular, I don't understand why it picks >> >> > template-haskell 2.6.0.0 when there's a newer version (2.7.0.0). As >> >> > far >> >> > as I >> >> > can see, QuickCheck doesn't put an upper limit on its template >> >> > haskell >> >> > version dependency. >> >> > >> >> > I'd appreciate any pointers with this. (Googling and questions on the >> >> > #haskell irc channel didn't help much, unfortunately.) >> >> > >> >> > -Levent. >> >> > >> >> > >> >> > _______________________________________________ >> >> > Haskell-Cafe mailing list >> >> > Haskell-Cafe(a)haskell.org >> >> > http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > >> >> >> >> _______________________________________________ >> >> Haskell-Cafe mailing list >> >> Haskell-Cafe(a)haskell.org >> >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >> > >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Re: [Haskell-cafe] Cabal install fails due to recent HUnit
by Simon Hengel 19 Jul '12

19 Jul '12

On Wed, Jul 18, 2012 at 05:51:51PM -0600, Richard G. wrote: > What's the best way to fix this? I can see two options: > - Move the test stanzas to a different Cabal file, allowing users to > perform the tests with a little fiddling. > - Remove the conditional statements from the test stanzas, which may > break compatibility with some compilers and interpreters. > > Is there another option? I think it is preferable to have a test section in the main cabal file. Just an idea: What about having just a single test suite that *depends on the library*? I think that way the test suit would not require any conditionals, but you could not test with different optimization levels anymore. We could then add a Makefile/script that configures, builds and tests with the different optimization levels. This approach also has the advantage, that we are testing exactly the same thing (the library!) that the user is going to use. Cheers, Simon

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Haskell Weekly News: Issue 236
by Daniel Santa Cruz 18 Jul '12

18 Jul '12

Welcome to issue 236 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of July 8 to 14, 2012. Quotes of the Week * RichardBuckminsterFuller: When I am working on a problem, I never think about beauty. But when I have finished, if the solution is not beautiful, I know that it is wrong. * Taneb: I'm doing the thing that every bored haskeller does one day and rewriting Prelude Top Reddit Stories * Haskell Performance Patterns Domain: johantibell.com, Score: 71, Comments: 34 On Reddit: [1] http://goo.gl/gZkMB Original: [2] http://goo.gl/2rj4t * Code Us Some Roguelike in Haskell! Domain: jamiltron.com, Score: 55, Comments: 19 On Reddit: [3] http://goo.gl/VYOx1 Original: [4] http://goo.gl/OOiSG * I never tested this code before releasing it Confession of a Haskell Hacker Domain: r6.ca, Score: 51, Comments: 48 On Reddit: [5] http://goo.gl/EBfT7 Original: [6] http://goo.gl/9zA0u * Breaking from a loop Domain: haskellforall.com, Score: 37, Comments: 19 On Reddit: [7] http://goo.gl/yqxqg Original: [8] http://goo.gl/NtI8j * The Classy Prelude, an alternate prelude which makes it easier to use conflicting names via typeclasses, and thereby encourages usage of more powerful libraries like text and unordered-containers. Domain: yesodweb.com, Score: 35, Comments: 46 On Reddit: [9] http://goo.gl/cZKM5 Original: [10] http://goo.gl/70d6R * The Long and Epic Journey of LambdaCase Domain: unknownparallel.wordpress.com, Score: 33, Comments: 52 On Reddit: [11] http://goo.gl/EAVXs Original: [12] http://goo.gl/ymkGy * How is this fibonacci-function memoized? Domain: stackoverflow.com, Score: 33, Comments: 1 On Reddit: [13] http://goo.gl/lo3LD Original: [14] http://goo.gl/wwHQb * errors-1.0: Simplified error handling Domain: haskellforall.com, Score: 30, Comments: 31 On Reddit: [15] http://goo.gl/tKzP1 Original: [16] http://goo.gl/O10hN * Influenced by Haskell Domain: griffsgraphs.com, Score: 30, Comments: 29 On Reddit: [17] http://goo.gl/6ptoi Original: [18] http://goo.gl/Nrz7K * Experience Report: Haskell in Computational Biology (Daniels, Gallant, Ramsey)[pdf 7 pp] Domain: eecs.tufts.edu, Score: 30, Comments: 11 On Reddit: [19] http://goo.gl/XsvMK Original: [20] http://goo.gl/TUdnL * == for Float not referentially transparent Domain: haskell.org, Score: 23, Comments: 51 On Reddit: [21] http://goo.gl/6qZ1J Original: [22] http://goo.gl/DR9TE * My second attempt at writing Haskell Domain: self.haskell, Score: 21, Comments: 27 On Reddit: [23] http://goo.gl/i7u3p Original: [24] http://goo.gl/i7u3p * Announcing split-channel « Melding Monads Domain: blog.melding-monads.com, Score: 20, Comments: 16 On Reddit: [25] http://goo.gl/XwHdl Original: [26] http://goo.gl/oh5Ce * Deriving the Y combinator from first principles Domain: wellnowwhat.net, Score: 18, Comments: 12 On Reddit: [27] http://goo.gl/5uxYN Original: [28] http://goo.gl/Q76lk * Announcing WAI 1.3! Domain: yesodweb.com, Score: 18, Comments: 11 On Reddit: [29] http://goo.gl/QD769 Original: [30] http://goo.gl/mQFBK Top StackOverflow Questions * How is this fibonacci-function memoized? votes: 43, answers: 3 Read on SO: [31] http://goo.gl/MGjr3 * What is the combinatory logic equivalent of intuitionistic type theory? votes: 39, answers: 0 Read on SO: [32] http://goo.gl/ki9nT * Does Haskell have return type overloading? votes: 15, answers: 5 Read on SO: [33] http://goo.gl/sBGWj * Is there a way to avoid unnecessary recursion? votes: 12, answers: 2 Read on SO: [34] http://goo.gl/Gk39e * Using vectors for performance improvement in Haskell votes: 12, answers: 2 Read on SO: [35] http://goo.gl/74KOH * Eliminate Haskell array bounds check for Bounded type? votes: 11, answers: 1 Read on SO: [36] http://goo.gl/CHDtJ * Having my cereal and parsing it too votes: 8, answers: 2 Read on SO: [37] http://goo.gl/1SG24 * How does HOpenGL behave with regards to other threads and TChans in Haskell? votes: 8, answers: 2 Read on SO: [38] http://goo.gl/dmoqc * Number of arguments and point-free in Haskell votes: 8, answers: 2 Read on SO: [39] http://goo.gl/8Z0B2 * Haskell: Design pattern: classes or pass functions votes: 7, answers: 3 Read on SO: [40] http://goo.gl/EO7tr * Haskell — sort list with impure function votes: 7, answers: 4 Read on SO: [41] http://goo.gl/o9kbc Until next time, Daniel Santa Cruz References 1. http://johantibell.com/files/haskell-performance-patterns.html#%281%29 2. http://www.reddit.com/r/haskell/comments/wjtms/haskell_performance_patterns/ 3. http://jamiltron.com/2012/07/Code_Us_Some_Roguelike_in_Haskell.html 4. http://www.reddit.com/r/haskell/comments/wd6p3/code_us_some_roguelike_in_ha… 5. http://r6.ca/blog/20120708T122219Z.html 6. http://www.reddit.com/r/haskell/comments/w7zd8/i_never_tested_this_code_bef… 7. http://www.haskellforall.com/2012/07/breaking-from-loop.html 8. http://www.reddit.com/r/haskell/comments/wfwyt/breaking_from_a_loop/ 9. http://www.yesodweb.com/blog/2012/07/classy-prelude 10. http://www.reddit.com/r/haskell/comments/wfiao/the_classy_prelude_an_altern… 11. http://unknownparallel.wordpress.com/2012/07/09/the-long-and-epic-journey-o… 12. http://www.reddit.com/r/haskell/comments/wbb69/the_long_and_epic_journey_of… 13. http://stackoverflow.com/q/11466284/1288 14. http://www.reddit.com/r/haskell/comments/whx2k/how_is_this_fibonaccifunctio… 15. http://www.haskellforall.com/2012/07/errors-10-simplified-error-handling.ht… 16. http://www.reddit.com/r/haskell/comments/w7xrv/errors10_simplified_error_ha… 17. http://griffsgraphs.com/2012/07/01/programming-languages-influences/ 18. http://www.reddit.com/r/haskell/comments/w9npe/influenced_by_haskell/ 19. http://www.eecs.tufts.edu/~ndaniels/Noah_files/mrfy_experience_report.pdf 20. http://www.reddit.com/r/haskell/comments/wf6xe/experience_report_haskell_in… 21. http://www.haskell.org/pipermail/glasgow-haskell-users/2012-July/022568.html 22. http://www.reddit.com/r/haskell/comments/wbsd3/for_float_not_referentially_… 23. http://www.reddit.com/r/haskell/comments/walg1/my_second_attempt_at_writing… 24. http://www.reddit.com/r/haskell/comments/walg1/my_second_attempt_at_writing… 25. http://blog.melding-monads.com/2012/07/10/announcing-split-channel/ 26. http://www.reddit.com/r/haskell/comments/wdhf1/announcing_splitchannel_meld… 27. http://www.wellnowwhat.net/blog/?p=485 28. http://www.reddit.com/r/haskell/comments/wd5rb/deriving_the_y_combinator_fr… 29. http://www.yesodweb.com/blog/2012/07/announcing-wai-1-3 30. http://www.reddit.com/r/haskell/comments/wih94/announcing_wai_13/ 31. http://stackoverflow.com/questions/11466284/how-is-this-fibonacci-function-… 32. http://stackoverflow.com/questions/11406786/what-is-the-combinatory-logic-e… 33. http://stackoverflow.com/questions/11420126/does-haskell-have-return-type-o… 34. http://stackoverflow.com/questions/11454936/is-there-a-way-to-avoid-unneces… 35. http://stackoverflow.com/questions/11481675/using-vectors-for-performance-i… 36. http://stackoverflow.com/questions/11411797/eliminate-haskell-array-bounds-… 37. http://stackoverflow.com/questions/11424961/having-my-cereal-and-parsing-it… 38. http://stackoverflow.com/questions/11443824/how-does-hopengl-behave-with-re… 39. http://stackoverflow.com/questions/11487171/number-of-arguments-and-point-f… 40. http://stackoverflow.com/questions/11423749/haskell-design-pattern-classes-… 41. http://stackoverflow.com/questions/11469806/haskell-sort-list-with-impure-f…

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HDBC nested withTransaction
by Andras Gyomrey 18 Jul '12

18 Jul '12

Hi, are there any plans of implementing nested transactions using withTransaction in HDBC? In mysql exists checkpoints and in postgres explicit subtransactions, Andras Gyomrey

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strange hangs with -threaded runtime
by Joey Hess 18 Jul '12

18 Jul '12

I have a rather large program that works fine with ghc's default runtime, but now I'd like to build it with -threaded, and this causes it to hang in a way I have not been able to pin down to anything specific. It hangs at different points each time it's run; running it in strace will consistently avoid the problem. If I look at it once it's hung, I always see a pair of processes, both blocked in futex: joey@wren:~/src/git-annex>strace -p 21749 Process 21749 attached - interrupt to quit futex(0x8b03930, FUTEX_WAIT_PRIVATE, 69, NULL^C <unfinished ...> Process 21749 detached joey@wren:~/src/git-annex>strace -p 21811 Process 21811 attached - interrupt to quit futex(0x8b03df8, FUTEX_WAIT_PRIVATE, 2, NULL Are there any common gotchas with converting to the threaded runtime that might provide a hint to what's wrong? My code does not currently use Control.Concurrent or threads, although it does use some libraries like MissingH that use forkIO or forkOS. GHC 7.4.1, 7.4.2 on Debian Linux -- see shy jo

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Haskell Symposium 2012 - Call for Participation (early registration closes 9th August)
by Janis Voigtländer 18 Jul '12

18 Jul '12

==================================================================== CALL FOR PARTICIPATION ACM SIGPLAN Haskell Symposium 2012 Copenhagen, Denmark 13th September, 2012 (directly after ICFP) http://www.haskell.org/haskell-symposium/2012/ ==================================================================== The purpose of the Haskell Symposium is to discuss experiences with Haskell and future developments for the language. The scope of the symposium includes all aspects of the design, semantics, theory, application, implementation, and teaching of Haskell. Accepted papers and programme: ============================== * http://haskell.org/haskell-symposium/2012/#schedule REGISTRATION IS NOW OPEN: ========================= * http://www.icfpconference.org/icfp2012/registration.html * Early registration deadline: 9th August, 2012 Local arrangements (including travel and accommodation): ======================================================== * http://www.icfpconference.org/icfp2012/local.html See you in Copenhagen, Janis Voigtlaender Haskell 2012 Programme Chair ====================================================================

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Re: [Haskell-cafe] Interest in typed relational algebra library?
by oleg＠okmij.org 18 Jul '12

18 Jul '12

> And yes to first order predicate calculus too! Just two weeks ago Chung-chieh Shan and I were explaining at NASSLLI the embedding in Haskell of the higher-order predicate logic with two base types (so-called Ty2). The embedding supports type-safe simplification of formulas (which was really needed for our applications). The embedding is extensible: you can add models and more constants. http://okmij.org/ftp/gengo/NASSLLI10/course.html#semantics

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