- Haskell-Cafe - Haskell.org

WANTED: grey line layout boxes in vim and emacs
by dons＠cse.unsw.edu.au 20 Dec '06

20 Dec '06

I'd like some more help from the editors in getting 2d layout right without trying. Here's a mockup of vim with vertical grey bars delimiting layout: http://www.cse.unsw.edu.au/~dons/tmp/haskell+boxes.png Does anyone know how to get this effect in vim (or emacs)? Bonus points if the grey bars are draggable, changing the indenting. More bonus points for box-based navigation. -- Don

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Possible commercial FP/Haskell job
by dons＠cse.unsw.edu.au 20 Dec '06

20 Dec '06

Noticed this in the blargh-o-sphere, some people might be interested: http://www.nnseek.com/e/comp.lang.python/lisp_python_programmers_among_othe… Senior applications developer: Our advanced applications work is currently being done in Common Lisp, but that could change depending on who we find to fill this position. If you are the sort of person who has always wanted an opportunity to prove that Haskell or OCaml is the Best Way to write software, this could be your chance. But CL is currently our first choice. -- Don

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Haskell Weekly News: December 20, 2006
by dons＠cse.unsw.edu.au 20 Dec '06

20 Dec '06

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20061220 Issue 54 - December 20, 2006 --------------------------------------------------------------------------- Welcome to issue 54 of HWN, a weekly newsletter covering developments in the Haskell community. A new release of the Edison data structures library, along with several other new libraries, and some new Haskell articles in the blogspace. Announcements Edison 1.2.1. Robert Dockins [1]announced the 1.2.1 release of [2]Edison. Edison is a famous library of efficient, purely-functional data structures in Haskell. Notable changes from the previous version include: a new sequence implementation based on finger trees; documentation fixes dealing with the licence; added a few methods to EnumSet for wrapping and unwrapping the underlying Word 1. http://article.gmane.org/gmane.comp.lang.haskell.general/14662 2. http://www.eecs.tufts.edu/~rdocki01/ Basic serialisation library using SYB. Stefan O'Rear [3]announced GenericSerialize, [4]a library for serialization using the existing generic-programming framework. It is often advocated that support for serialization should be added to the compiler (e.g. in the form of a deriving(Binary)). With this project Stefan wants to show that the existing infrastructure is sufficient, and has some advantages over a dedicated serialization interface. GenericSerialize supports multiple serialization modes. 3. http://article.gmane.org/gmane.comp.lang.haskell.general/14656 4. http://members.cox.net/stefanor/genericserialize vty 1.0. Stefan O'Rear [5]announced vty 1.0, a simple [6]terminal interface library. It provides: handling of suspend/resume, window resizes, computation of minimal differences, minimizes repaint area, automatically decodes keyboard keys into (key,modifier) tuples, and more! 5. http://article.gmane.org/gmane.comp.lang.haskell.general/14670 6. http://members.cox.net/stefanor/vty Monad.Reader call for copy. Wouter Swierstra [7]reminded us that its still not too late to write something for the next issue of [8]The Monad.Reader! We have a nice issue slowly shaping up, but your contribution is still very welcome. Get in touch with Wouter if you intend to submit something -- the sooner you let him know what you're up to, the better. 7. http://article.gmane.org/gmane.comp.lang.haskell.general/14638 8. http://www.haskell.org/haskellwiki/TheMonadReader Ranged Sets. Paul Johnson [9]announced that Ranged Sets now have a Monoid instance, and singletons (i.e. a range holding a single value), thanks to Jean-Philippe Bernardy. 9. http://article.gmane.org/gmane.comp.lang.haskell.general/14663 CalDims 1.0 (RC 1). schneegloeckchen [10]announced CalDims, a calculator aware of units. Its available from [11]the Haskell wiki. It includes support for user defined basic units and derrived units; user defined functions; work sheets can be modified/saved via shell; (1/3)*3 == 1 (No rounding errors); built-in feature to simplify units and easy unit-conversion. 10. http://article.gmane.org/gmane.comp.lang.haskell.general/14671 11. http://www.haskell.org/haskellwiki/CalDims JoinCabal. Dougal Stanton [12]announced an alternative to mkcabal, for initialising new cabal projects: [13]JoinCabal, available [14]via darcs. JoinCabal will create stub sources files with a license header, and appropriate license for you code, making it easier to set up a valid cabal build system. 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/17600 13. http://brokenhut.no-ip.org/~dougal/cgi-bin/darcsweb.cgi?r=JoinCabal;a=summa… 14. http://brokenhut.no-ip.org/~dougal/darcs/joincabal/ Haskell Vim plugin. Arthur van Leeuwen [15]announced a new [16]vim plugin for Haskell providing some preliminary folding support, easy insertion of type signatures into programs, and support for handling .hi files. 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/17675 16. http://www.cs.uu.nl/~arthurvl/haskell.vba Haskell' This section covers the [17]Haskell' standardisation process. * [18]Strictly matching monadic let and overloaded Bool 17. http://hackage.haskell.org/trac/haskell-prime 18. http://thread.gmane.org/gmane.comp.lang.haskell.prime/1956/focus=1974 Discussion Automonadization of code. Adam Megacz [19]asked if there any work on automatic translation of code in some tiny imperative language into Haskell code that uses the ST and/or IO monads (or perhaps even pure functional code)? 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/17326/focus=17326 What are the points in pointfree style?. Steve Downey [20]wondered about the origin of the term 'points' in pointfree style. 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/17560/focus=17560 Rebinding >>= for restricted monads. David Roundy [21]pondered rebinding the >>= syntax in order to provide a more restricted monad. 21. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/17646/focus=17646 #haskell reaches 300 users. Don Stewart [22]noticed that the [23]#haskell IRC channel has now reached the 300 user mark, making it one of the top 15 channels on the freenode network. 22. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/17705/focus=17705 23. http://haskell.org/haskellwiki/IRC_channel Blog noise [24]Haskell news from the blogosphere. * [25]Do-notation considered harmful * [26]Reddit discussion considered productive * [27]The Dot-Matrix Printhead: a Haskell Toy * [28]The Revised Dot-Matrix Printhead * [29]The monad laws * [30]On documentation * [31]Software requirements do not change * [32]Haskell and the web: some ideas in progress * [33]Using Haskell in Python: haskellembed * [34]Literate programming * [35]The lambda revolution, Episode V, the deb strikes back * [36]On syntax * [37]Syntax: adding Lisp macros * [38]More on syntax * [39]UCBLogo and the Fibonacci sequence * [40]Linguistic comparisons: string reversal * [41]New Software Technology: Blockage On Line * [42]More silver bullets * [43]Preventing NullPointerExceptions, Maybe * [44]Adventures in Haskell: the Parsec magic weapon * [45]Advertising Haskell * [46]Programming Haskell: part 1 * [47]Programming Haskell: part 2 * [48]Programming Haskell: part 3 * [49]Introductory Haskell Programming in the UNIX Environment * [50]On Haskell, Intuition And Expressive Power * [51]Your order is ready sir * [52]It's alive (the French Haskell community) * [53]Maybe monad in Java * [54]Secret Santas in Haskell I: Preliminaries * [55]Secret Santas in Haskell II: Orbits and Lists * [56]Why Closures in Dolphin is a Good Idea * [57]Haskell Stacks : Two Different Ways * [58]Haskell Golf Scores * [59]Languages * [60]Questions on Haskell Style (and Polynomials redux) * [61]A simple RSS aggregator in 50 lines of Haskell using HXT 24. http://planet.haskell.org/ 25. http://syntaxfree.wordpress.com/2006/12/12/do-notation-considered-harmful/ 26. http://syntaxfree.wordpress.com/2006/12/13/reddit-discussion-considered-pro… 27. http://praisecurseandrecurse.blogspot.com/2006/12/dot-matrix-printhead-hask… 28. http://praisecurseandrecurse.blogspot.com/2006/12/revised-dot-matrix-printh… 29. http://cale.yi.org/index.php/The_Monad_Laws 30. http://blog.milkfarmsoft.com/?p=29 31. http://blog.tmorris.net/software-requirements-do-not-change/ 32. http://haskell-web.blogspot.com/2006/12/some-ideas-in-progress_13.html 33. http://www.kuarepoti-dju.net/index.php?p=86 34. http://benjisimon.blogspot.com/2006/12/programs-as-stories.html 35. http://pupeno.com/blog/the-lambda-revolution-episode-v-the-deb-strikes-back 36. http://cgi.cse.unsw.edu.au/~dons/blog/2006/12/14#on-syntax 37. http://nominolo.blogspot.com/2006/12/syntax.html 38. http://www.cse.unsw.edu.au/~dons/blog/2006/12/15#on-syntax-again 39. http://sob.apotheon.org/?p=171 40. http://sob.apotheon.org/?p=170 41. http://cogito.blogthing.com/2006/12/14/new-software-technology-blockage-on-… 42. http://clabs.org/blogki/blogki.cgi?page=/ComputersAndTechnology/AndTheNomin… 43. http://rickyclarkson.blogspot.com/2006/09/using-strong-typing-to-eliminate.… 44. http://jpmoresmau.blogspot.com/2006/12/adventures-in-haskell-parsec-magic.h… 45. http://neilmitchell.blogspot.com/2006/12/advertising-haskell.html 46. http://cgi.cse.unsw.edu.au/~dons/blog/2006/12/16#programming-haskell-intro 47. http://www.cse.unsw.edu.au/~dons/blog/2006/12/17#programming-haskell-part-2 48. http://cgi.cse.unsw.edu.au/~dons/blog/2006/12/18#ph-3 49. http://blog.kfish.org/software/haskell/intro-haskell-unix.html 50. http://www.defmacro.org/ramblings/haskell-productivity.html 51. http://lambda-the-ultimate.org/node/1905#comment-23273 52. http://koweycode.blogspot.com/2006/12/its-alive.html 53. http://blog.tmorris.net/maybe-monad-in-java/ 54. http://mult.ifario.us/articles/2006/12/18/secret-santas-in-haskell-i-prelim… 55. http://mult.ifario.us/articles/2006/12/18/secret-santas-in-haskell-ii-orbit… 56. http://rickyclarkson.blogspot.com/2006/12/why-closures-in-dolphin-is-good-i… 57. http://progexpr.blogspot.com/2006/11/haskell-stacks-two-different-ways.html 58. http://progexpr.blogspot.com/2006/11/haskell-golf-scores.html 59. http://computativestylings.blogspot.com/2006/12/languages.html 60. http://sambangu.blogspot.com/2006/12/questions-on-haskell-style-and 61. http://cale.yi.org/index.php/HRSS Quotes of the Week * Cale: I spent a whole summer being paid to write a nondeterministic search program in the list monad * monochrom: 007 titles for Haskellers: fromForeignPtr withCString; You Only lift Twice; Bottoms Are Forever; The Monad with the Pure Function; For Your Types Only; A view to A seq; Licence to killThread; iterate Never Dies; unsafePerformIO Is Not Enough. * DavidRoundy: ... fun of haskell-cafe is that it's where all the cool people hang out * dons: Coding drunk in Haskell is ok though, its like drinking on a passenger plane flight -- the stewards will prevent you from hurting anyone. However, coding drunk in C is just scary, DUI territory, and should not be allowed. * JulianMorrison: Small startup companies are the expendable sensory and feeding apparatus of the mainstream. * droundy: With a higher-kinded monad and phantom existential witness types, darcs would be very fun... * dons: The alien rulers of the galaxy must surely use a statically typed language with type inference * dibblego: Java programmers prefer referential transparency too, they just call it 'design patterns' or something * tessier: After the last newbies head exploded trying to read everything on that monad link there was a lot of paperwork. We'd like to avoid doing that again. Code Watch Fri Dec 8 21:03:34 PST 2006. Andy Gill. [62]Adding tracing support (HPC) 62. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/18263 Wed Dec 13 08:45:38 PST 2006. simonpj. [63]You can now have an MVar with a polymorphic contents 63. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/18279 About the Haskell Weekly News Each week, new editions are posted to [64]the Haskell mailing list as well as to [65]the Haskell Sequence and [66]Planet Haskell. [67]RSS is also available, and headlines appear on [68]haskell.org. Headlines are available as [69]PDF. The Haskell Weekly News is also [70]available in Spanish translation. To help create new editions of this newsletter, please see the [71]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [72]http://www.cse.unsw.edu.au/~dons/code/hwn 64. http://www.haskell.org/mailman/listinfo/haskell 65. http://sequence.complete.org/ 66. http://planet.haskell.org/ 67. http://sequence.complete.org/node/feed 68. http://haskell.org/ 69. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20061220.pdf 70. http://haskell.org/haskellwiki/HWN/es 71. http://haskell.org/haskellwiki/HWN 72. http://www.cse.unsw.edu.au/~dons/code/hwn

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howto c2hs marshall in out argument by reference
by Marc Weber 19 Dec '06

19 Dec '06

The function takes a pointer to an integer, prints its value and returns the increment. void cl_inc(int *i){ printf("changing int from %d to %d", *i, (++i)); } I've managed it by using this code: {#fun pure cl_inc {alloca `CInt' peek*} -> `()'#} -} and calling it this way: alloca $ \mem -> do poke mem 3; print_int_ptr_value mem then its a matter of reading mem by using peak again. Is there a better way letting {#func do the marshalling to be able to do directly? print $ cl_inc 3 4 Marc

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Data.Generics question
by Grote Collective 19 Dec '06

19 Dec '06

Hello all, I have two datatypes, both representing the same language. However, one is a "flattened" version of the other. For instance: data Flattened = Const Flattened | Sum Flattened Flattened | ... | IntConst Int | RealConst Float | BoolConst Bool | Void ---- data Term = Const Constant | Sum Term Term | ... data Constant = IntConst Int | RealConst Float | BoolConst Bool | Void Now I want to create functions to convert between these two datatypes. This is easy to do but *very* tedious in its most naive approach. However, I think I can use Data.Generics to make a simple implementation of both functions. The question is: can I? I think that this conversion is a simple fold over the structure, changing merely the constructor name (the qualified name, because the unqualified name is the same), but I cannot seem to understand from the documentation how to do this... Thanks in advance, Mark Smith

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Class annotation on datatype ineffective in function
by Reto Kramer 19 Dec '06

19 Dec '06

The code below does not compile unless the "bar" function is annotated with a suitable constraint on the class of the formal parameter. > module Main where > > class (C a) > data (C foo) => XY foo = X foo | Y foo > > bar :: a -> XY a > bar aFoo = X aFoo > > main = return () I get: > $ ghc Test.hs > > Test.hs:8:8: > No instance for (C a) > arising from use of `X' at Test.hs:8:8-10 > Possible fix: add (C a) to the type signature(s) for `foo' > In the expression: X a > In the definition of `foo': foo a = X a As suggested, this works: > bar :: (C a) => a -> XY a Can someone explain to me why the compiler can not infer that "a" (in bar) must be (C a) from the bar result type "XY a" (by way of the "C class" provided for the datatype)? Thanks, - Reto

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On the various faces of Composition
by Jacques Carette 19 Dec '06

19 Dec '06

[As recently seen on LtU - http://lambda-the-ultimate.org/node/1919] An amazing paper http://www.dbmcintyre.pwp.blueyonder.co.uk/index_f/menu_f/j_f/apl95.pdf on "composition" as seen from APL and J. The terminology (using verbs, nouns, adverbs, etc) is _so_ much more evocative than the terminology used for similar ideas here, I hope that some of it can rub off. Also, if anyone thought that "point free" programming was something mostly-recent, mostly-Haskell, they _really_ need to read this paper! Also, I am fairly sure that some of the high-powered operators in J may stress Haskell's type system quite severely, if not to the breaking point. It would be a fascinating exercise to try to reproduce the various examples in that paper in as-idiomatic-as-possible Haskell. While J's syntax is somewhat on the terse side, its power regarding practical mathematics is superb -- especially when it comes to polymorphism. Jacques

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exception output
by Ferenc Wagner 19 Dec '06

19 Dec '06

Hi, the following program main = readFile "nonexistent" >>= putStr is meant to produce an exception. When compiled with GHC 6.4, it outputs the "*** Exception..." string to stderr, which makes me happy. However, when run with runghc6 or runhugs, the message is sent to stdout, which makes me sad. Is this inconsistency intentional? -- Thanks, Feri.

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Re: [Haskell-cafe] Data.Generics question
by Vyacheslav Akhmechet 19 Dec '06

19 Dec '06

Sorry, I sent the email to the wrong place and messed up the code (it's early :)). Take two: transform = everywhere (mkT transform') where transform = (\Term a->Flattened a) `extT` (Contstant a->Flattened a) On 12/19/06, Vyacheslav Akhmechet <coffeemug(a)gmail.com> wrote: > That should be pretty simple. This code probably won't work, but you > can use it as an example to look into this further. > > transform everywhere = (mkT transform') > where transform = (\Term a->Flattened a) > `extT` (Contstant a->Flattened a) > > Something like this should work. Look into the docs for more info. > > On 12/19/06, Grote Collective <grotecollective(a)gmail.com> wrote: > > Hello all, > > > > I have two datatypes, both representing the same language. However, one is a > > "flattened" version of the other. For instance: > > > > data Flattened = > > Const Flattened > > | Sum Flattened Flattened > > | ... > > | IntConst Int > > | RealConst Float > > | BoolConst Bool > > | Void > > > > ---- > > > > data Term = > > Const Constant > > | Sum Term Term > > | ... > > > > data Constant = > > IntConst Int > > | RealConst Float > > | BoolConst Bool > > | Void > > > > > > Now I want to create functions to convert between these two datatypes. This > > is easy to do but *very* tedious in its most naive approach. However, I > > think I can use Data.Generics to make a simple implementation of both > > functions. The question is: can I? I think that this conversion is a simple > > fold over the structure, changing merely the constructor name (the qualified > > name, because the unqualified name is the same), but I cannot seem to > > understand from the documentation how to do this... > > > > Thanks in advance, > > Mark Smith > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > >

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maybeToM
by Joachim Breitner 19 Dec '06

19 Dec '06

Hi, dons mentions in his blog post that Data.Map’s lookup is generalized over the Monads, whereas Prelude.maybe isn’t. Are there good reasons not to do that to Prelude.maybe as well? Alternatively, how about adding this function to Data.Maybe, analogous to maybeToList > maybeToM Nothing = fail "Nothing" > maybeToM (Just x) = return x (Incidentially, this function is the same as maybeToList if run in the List Monad). This way, Prelude.lookup (or any function that returns a Maybe) can be generalized as (maybeToM . lookup). Greetings, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: joachimbreitner(a)amessage.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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