October 2009 - Haskell-Cafe

a library for control of terminal driver modes?
by Iain Barnett 13 Oct '09

13 Oct '09

I'm looking for a library like Perl's Term-Readkey, so that I can turn on and off the echo for secure password input from a terminal. Anyone know which library I need to use for this? Iain

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<**> for nested applicative functors?
by Kim-Ee Yeoh 13 Oct '09

13 Oct '09

Does anyone know if it's possible to write the following: <**> :: (Applicative m, Applicative n) => m (n (a->b)) -> m (n a) -> m (n b) Clearly, if m and n were monads, it would be trivial. Rereading the original paper, I didn't see much discussion about such nested app. functors. Any help appreciated. -- View this message in context: http://www.nabble.com/%3C**%3E-for-nested-applicative-functors--tp25858792p… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: ANN: CmdArgs - easy command line argument processing
by Ben Franksen 13 Oct '09

13 Oct '09

Neil Mitchell wrote: > I am pleased to announce CmdArgs v0.1. CmdArgs is a library for easy > command line argument processing - taking the arguments passed into > your program from getArgs and converting them into a structured value > for use in your program. Compared to the System.Console.GetOpts > library there are two key advantages: > > 1) The command line argument processors are shorter - in a typical > case they are about 1/3 the size, 90 lines with getopts vs 30 simpler > lines with CmdArgs (for HLint). > > 2) CmdArgs can support multiple mode command lines, such as those > found in hpc, darcs and cabal. > > The guiding principle of CmdArgs is to try and write each piece of > information only once, which makes the command line processing > shorter, and eliminates many of the accidental copy-and-paste style > bugs that are easy with getopts. CmdArgs requires GHC, but other than > this restriction, I do not foresee any reason for anyone to use > getopts over CmdArgs. I very much like the general idea of this thing, but have a question regarding the interface. This is from the docs: (&=) :: a -> Attrib -> a Add attributes to a value. Always returns the first argument, but has a non-pure effect on the environment. Take care when performing program transformations. value &= attrib1 & attrib2 To expose an impure function (!) in an API, I don't know... I mean, couldn't one just wrap the value like this data Attributed a -- opaque (&=) :: a -> Attrib -> Attributed a mode :: Data a => Attributed a -> Mode a and thus retain a purely functional interface? Cheers Ben

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Haskell-tan competition
by Svein Ove Aas 13 Oct '09

13 Oct '09

I say "competition", but.. at the moment I'm only aware of a single Haskell-tan, namely the one at http://www.reddit.com/r/programming/comments/9ss7n/haskell%E3%82%BF%E3%83%B…. This cannot stand. Haskell needs an anthropomorphized personification, like any other modern language. Anyway, have any of you seen any others? -- Svein Ove Aas

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Re: MTL vs Transformers?
by John Lato 13 Oct '09

13 Oct '09

> From: Erik de Castro Lopo <mle+hs(a)mega-nerd.com> > > Well Iteratee built with MTL passes all the tests that shipped with it > so I suppose it must be correct. > Unfortunately the iteratee tests aren't exhaustive, but if it builds with MTL it should work. I'm more surprised that it built just by changing the .cabal file; I would expect you'd have to hack up the imports in the source code. John

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MTL vs Transformers?
by Erik de Castro Lopo 13 Oct '09

13 Oct '09

Hi all, I've just received the following error message: headers.hs:6:7: Could not find module `Control.Monad.Identity': it was found in multiple packages: transformers-0.1.4.0 mtl-1.1.0.2 I'm trying to use the Iteratee module which depends on Transformers but I use MTL in other stuff. Whats the preferred solution here? Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Why MTL and Transformers?
by Gregory Crosswhite 13 Oct '09

13 Oct '09

Something that I have been wondering for a while is: why are there *still* two monad transformer libraries with seemingly identical functionality, especially given that they have conflicting namespaces? It creates stupid problems like the one that Erik encountered and had to work around. I recognize that this situation most likely came about via historical accident rather than by intention, but why does it continue to be true? Cheers, Greg

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Haskell Weekly News: Issue 134 - October 10, 2009
by jfredett＠gmail.com 13 Oct '09

13 Oct '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091010 Issue 134 - October 10, 2009 --------------------------------------------------------------------------- Welcome to issue 134 of HWN, a newsletter covering developments in the [1]Haskell community. What with Don Stewart's [2]call to [3]arms to lead Haskell to conquest over (E)DSL-land, I've once again tried to highlight discussion of EDSL's this week. Fortunately, it was actually more difficult choosing what _not_ to include this week, since there was so much discussion about DSLs and Syntax extensions (a related notion, in my opinion). Also, this week Bryan O'Sullivan put his Criterion Library to good use on the `text` package, leading to [4]code which is more than ten times faster than before! With all this fantastic news, I won't hold you up any longer, Haskellers, the Haskell Weekly News! Announcements CfPart: FMICS 2009, 2-3 November 2009, Final Call. FMICS 2009 workshop chair [5]announced the final call for particpaction for FMICS 2009 ICFP videos now available. Wouter Swierstra [6]announced the availablity of videos from the International Conference on Functional Programming (ICFP) GPipe-1.0.0: A functional graphics API for programmable GPUs. Tobias Bexelius [7]announced the first release of GPie, a functional graphics API for programmable GPUs. text 0.5, a major revision of the Unicode text library. Bryan O'Sullivan [8]announced a new, major version of the text package. New API features, and huge improvments in speed, as Bryan says, 'Get it while it's fresh on Hackage, folks!' vty-ui 0.2. Jonathan Daugherty [9]announced a new version of the vty-ui package, with fewer bugs, more widgets, and cleaner code due to new more powerful abstractions. htzaar-0.0.1. Tom Hawkins [10]announced HTZAAR, a Haskell implementation of TZAAR Graphalyze-0.8.0.0 and SourceGraph-0.5.5.0. Ivan Lazar Miljenovic [11]announced To keep this editor happy, Ivan released two new packaged in one announcement. This time, he's added Legend support to Graphalyze, but also many new changes to SourceGraph, including a legend so you can see what all the symbols mean, Better color support, and much more. TxtSushi 0.4.0. Keith Sheppard [12]announced a new version of TxtSushi, a set of command line utilities for processing CSV and TSV files. Discussion Applicative do? Philippa Cowderoy [13]asked about a `do` like syntax for Applicative functors. How to add use custom preprocessor in cabal. Bernd Brassel [14]asked how to add a custom preprocessor to the build chain of a cabal file. On DSLs - one last time. Gunther Schmidt [15]summarized his impressions on al the recent discussion of DSLs What is a DSL? Oleg [16]offered some insight into different [17]properties that can be part of a single tagless framework. He also pointed to some slides and other materials such as a website [18]here and slides [19]here about DSL implementations and definitions. What is a DSL? Gunther Schmidt [20]posed the question, 'What is a DSL', and with some further questions added by yours truly, a lively discussion about the definition of a DSL ensued. Finally tagless - stuck with implementation of 'lam'. Gunther Schmidt [21]asked another question about Finally Tagless DSLs and resolving an issue with the implementation of 'lam' Blog noise [22]Haskell news from the [23]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Darcs: [24]darcs weekly news #43. * JP Moresmau: [25]What client for an Haskell Multi Player Game?. * Mikael Vejdemo Johansson (Syzygy-): [26][MATH198] Third lecture is up. * Bryan O'Sullivan: [27]Announcing a major revision of the Haskell text library. * Eric Kow (kowey): [28]darcs hashed-storage work merged (woo!). * David Amos: [29]Symmetries of PG(n,Fq). * The GHC Team: [30]Parallelism /= Concurrency. * >>> Nefigah: [31]Fake World Haskell. Nefigah, a recent addition to the community, has been working through RWH, and is providing some excellent examples. Though, This editor prefers the title 'Real Life Haskell' as opposed to his choice. * Tom Schrijvers: [32]Release 0.6 of Monadic Constraint Programming. * Neil Brown: [33]Concurrency Can Be Deterministic (But The Type System Doesn't Know It). * Clint Moore: [34]Curiously Parallel. * Galois, Inc: [35]Tech Talk: Constructing A Universal Domain for Reasoning About Haskell Datatypes. * Neil Brown: [36]Terminal Concurrency: The Printing Process. * Sean Leather: [37]'Upwards and downwards accumulations on trees' translated into Haskell. * Mikael Vejdemo Johansson (Syzygy-): [38][MATH 198] Second lecture. * Chris Smith: [39]View Patterns as Pattern Matching for Records. * Chris Smith: [40]Playing With Records. * FP Lunch: [41]Left Kan extensions of containers. Quotes of the Week * Baughn: Blum Blum Shub, a PRNG derived from poking around R'Lyeh. * ksf: * lambdabot locks up ksf in a Monad <ksf> mmmmh it's warm and fuzzy in here. * monochrom: Don't wrap your head around Haskell. Immerse! Wrap Haskell around your head. * chak: ... In other words, FP is inevitable. * robreim: I'm in your base hacking all your lambdas * gwern: RAM is overrated, swap is where it's at ;) * idnar: [to gwern] swap to a ramdisk! ;P About the Haskell Weekly News New editions are posted to [42]the Haskell mailing list as well as to [43]the Haskell Sequence and [44]Planet Haskell. [45]RSS is also available, and headlines appear on [46]haskell.org. To help create new editions of this newsletter, please see the information on [47]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [48]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://www.haskell.org/pipermail/haskell-cafe/2009-October/067203.html 3. http://www.reddit.com/r/haskell/comments/9qk54/haskell_should_own_the_edsl_… 4. http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17555 6. http://article.gmane.org/gmane.comp.lang.haskell.general/17552 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17546 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64591 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64529 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64516 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64399 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64301 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64616 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64558 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64552 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64533 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/ 18. http://dsl09.blogspot.com/ 19. http://dsl09.blogspot.com/2009/07/panel.html 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64474 21. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64343 22. http://planet.haskell.org/ 23. http://haskell.org/haskellwiki/Blog_articles 24. http://blog.darcs.net/2009/10/darcs-weekly-news-43.html 25. http://jpmoresmau.blogspot.com/2009/10/what-client-for-haskell-multi-player… 26. http://blog.mikael.johanssons.org/archive/2009/10/math198-third-lecture-is-… 27. http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… 28. http://koweycode.blogspot.com/2009/10/darcs-hashed-storage-work-merged-woo.… 29. http://haskellformaths.blogspot.com/2009/10/symmetries-of-pgnfq.html 30. http://ghcmutterings.wordpress.com/2009/10/06/parallelism-concurrency/ 31. http://my.life-is-virtual.com/2009/10/07/fake-world-haskell-part-1/ 32. http://tomschrijvers.blogspot.com/2009/10/release-06-of-monadic-constraint.… 33. http://chplib.wordpress.com/2009/10/07/concurrency-can-be-deterministic/ 34. http://www.l2mlogistics.com/2009/10/curiously-parallel.html 35. http://www.galois.com/blog/2009/10/06/huffman-universal/ 36. http://chplib.wordpress.com/2009/10/06/the-printing-process/ 37. http://feedproxy.google.com/~r/splonderzoek/~3/4E8TZPDZ-aM/upwards-and-down… 38. http://blog.mikael.johanssons.org/archive/2009/10/math-198-second-lecture/ 39. http://cdsmith.wordpress.com/2009/10/04/view-patterns-as-pattern-matching-f… 40. http://cdsmith.wordpress.com/2009/10/03/playing-with-records/ 41. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=237 42. http://www.haskell.org/mailman/listinfo/haskell 43. http://sequence.complete.org/ 44. http://planet.haskell.org/ 45. http://sequence.complete.org/node/feed 46. http://haskell.org/ 47. http://haskell.org/haskellwiki/HWN 48. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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Graph Library Using Associated Types
by Lajos Nagy 13 Oct '09

13 Oct '09

Hi, I understand that one of the original motivations for introducing associated types to Haskell was the survey of support for generic programming done by Garcia et al. where they compared the implementation of the Boost Graph Library in various languages (C++, Java, Haskell, ML, C#, Eiffel). Haskell got full marks in all categories, except for associated types which made the resulting implementations more verbose than necessary (and exposed implementation details). Since then GHC added support for associated types but I was wondering if anybody re-did the experiment with the new features enabled (the original code is available at: http://www.osl.iu.edu/research/comparing/) Regards, Lajos

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QuickCheck2 question
by Patrick Perry 12 Oct '09

12 Oct '09

I'm having some trouble with QuickCheck2 and Control.Applicative. Specifically, I have the following functions (slightly simplified): copyVector :: IOVector -> Vector -> IO () freezeVector :: IOVector -> IO (Vector) I have a test, part of which looks like monadicIO $ do run $ copyVector <$> pure dst <*> freezeVector src -- more stuff... When I try running the test (using test-framework-quickcheck2), the `copyVector` function never gets called. If I re-write the test as monadicIO $ do src' <- run $ freezeVector run $ copyVector dst src' -- etc. then everything works fine (i.e., the call to `copyVector` gets executed). Does anyone have any clues as to what is going on? I suspect the problem is related to Test.QuickCheck.Monadic using `unsafePerformIO` without a `{-# NOINLINE -#}` pragma [1], but I'm not completely sure. Adding such a pragma to `monadicIO` and `run` in Monadic.hs does not fix the problem. I'm using Quickcheck-2.1.0.2 and GHC 6.10.1. Thanks in advance for any help, Patrick [1] http://hackage.haskell.org/packages/archive/QuickCheck/2.1.0.2/doc/html/src…

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