March 2008 - Haskell-Cafe

concurrent definitions with parsec
by Zsolt SZALAI 10 Mar '08

10 Mar '08

Hi! I'm writing a parser for a language, with a BNF like this: Type = "type" Def Def = RecordDef | RecordOfDef ... RecordDef = "record" Body RecordOfDef = "record" "of" With a perser what uses parsec module it can be mapped to haskell easily: structuredTypeDef = recordDef <|> recordOfDef But this way, the recordOfDef case will never be parsed at a line like "type record <somethings>", because recordDef will win in the first place always. Is there an option or an other operation instead of <|> to do the trick? I cant see if the problem can be solved with parsecperm or not. It is a possibility to do something like swap "recordDef <|> recordOfDef" with "recordlikeDefs " where recordlikeDefs = do { reserved "record" ; others } but that would be the dirty way... Do you have any advise on the case? Thanks, -- Zsolt Szalai

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Issues(Bugs?) with GHC Type Families
by Hugo Pacheco 09 Mar '08

09 Mar '08

Hi all, I have recently tried to replicate some examples from in the articles about type families but found some possible bugs. In [2], the example class C a where type S a (k :: * -> *) :: * instance C [a] where type S [a] k = (a,k a) does not compile under the claim that the type variable k is not in scope. However, if we extract the type family from the class type family S a (k :: * -> *) :: * type instance S [a] k = (a, k a) class C a it compiles correctly. According to [3], the difference is purely syntactic sugar, does that mean that both examples should compile and behave the same or is there some subtlety that justifies the class example not to compile? Another issue is that data kinds (used in both [2] and [3]) do not seem to be supported at all by the compiler, are they already implemented in GHC? Simple examples such as datakind Nat = Zero or datakind Nat = Zero | Succ Nat fail to compile. Perhaps some of these should be submitted to the GHC Bug Tracker. I have tested both GHC 6.8.2 and 6.9.20080218. References: 1. Associated Types with Class.<http://www.cse.unsw.edu.au/~chak/papers/CKPM05.html> Manuel M. T. Chakravarty, Gabriele Keller, Simon Peyton Jones, and Simon Marlow. In *Proceedings of The 32nd Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL'05)*, pages 1-13, ACM Press, 2005. 2. Associated Type Synonyms.<http://www.cse.unsw.edu.au/~chak/papers/CKP05.html> Manuel M. T. Chakravarty, Gabriele Keller, and Simon Peyton Jones. In *Proceedings of The Tenth ACM SIGPLAN International Conference on Functional Programming *, ACM Press, pages 241-253, 2005. 3. Towards Open Type Functions for Haskell.<http://www.cse.unsw.edu.au/~chak/papers/SSPC07.html> Tom Schrijvers, Martin Sulzmann, Simon Peyton-Jones, and Manuel M. T. Chakravarty. Unpublished manuscript, 2007.

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Haskell Weekly News: March 09, 2008
by Don Stewart 09 Mar '08

09 Mar '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080309 Issue 71 - March 09, 2008 --------------------------------------------------------------------------- Welcome to issue 71 of HWN, a newsletter covering developments in the [1]Haskell community. Another busy week on the Haskell library front, with around 100 new and updated libraries and tools on Hackage. 1. http://haskell.org/ Announcements Google Summer of Code. Malcolm Wallace [2]announced Google is running its 'Summer of Code' project again this year, and Haskell.org is once again going to apply to be a mentoring organisation. If you're interested in earning money to hack on Haskell, and helping out the community, [3]take a look at the wiki. 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37273 3. http://hackage.haskell.org/trac/summer-of-code Haskell in the browser. Dimitry Golubovsky [4]announced that the YHC JavaScript backend is now in alpha testing, and is open to experimentation for those wanting to write Haskell directly for the browser 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37299 Hackage New and updated libraries in [5]the Hackage library database. 5. http://hackage.haskell.org/ * typalyze 0.1.1. Uploaded by Matthew Danish. [6]typalyze: Analyzes Haskell source files for easy reference. * lax 0.0.0.1. Uploaded by Wolfgang Jeltsch. [7]lax: Lax arrows. * truelevel 0.1.1. Uploaded by Barton Massey. [8]truelevel: Audio file compressor-limiter. * WAVE 0.1. Uploaded by Barton Massey. [9]WAVE: WAVE audio file IO library. * parseargs 0.1. Uploaded by Barton Massey. [10]parseargs: Command-line argument parsing library for Haskell programs. * conjure 0.1. Uploaded by Gwern Branwen. [11]conjure: A BitTorrent client. * Diff 0.1.1. Uploaded by Sterling Clover. [12]Diff: O(ND) diff algorithm in haskell.. * simseq 0.0. Uploaded by Gwern Branwen. [13]simseq: Simulate sequencing with different models for priming and errors. * rbr 0.8.3. Uploaded by Gwern Branwen. [14]rbr: Mask nucleotide (EST) sequences in Fasta format. * xml2x 0.2. Uploaded by Gwern Branwen. [15]xml2x: Convert BLAST output in XML format to CSV or HTML. 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/typalyze-0.1.1 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lax-0.0.0.1 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/truelevel-0.1.1 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/WAVE-0.1 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parseargs-0.1 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/conjure-0.1 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Diff-0.1.1 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/simseq-0.0 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rbr-0.8.3 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xml2x-0.2 * estreps 0.1. Uploaded by Gwern Branwen. [16]estreps: Repeats from ESTs. * clustertools 0.1. Uploaded by Gwern Branwen. [17]clustertools: Tools for manipulating sequence clusters. * xsact 1.6. Uploaded by Gwern Branwen. [18]xsact: Cluster EST sequences. * HsJudy 0.2. Uploaded by Gwern Branwen. [19]HsJudy: Judy bindings, and some nice APIs. * prof2dot 0.3.1. Uploaded by Gregory Wright. [20]prof2dot: Convert GHC profiles into GraphViz's dot format. * strict 0.3.2. Uploaded by Roman Leshchinskiy. [21]strict: Strict data types and String IO.. * Emping 0.4. Uploaded by Hans VanThiel. [22]Emping: derives heuristic rules from nominal data. * GuiHaskell 0.1.1. Uploaded by Neil Mitchell. [23]GuiHaskell: A graphical REPL and development environment for Haskell. * simpleargs 0.1. Uploaded by Ketil Malde. [24]simpleargs: Provides a more flexible getArgs function with better error reporting.. * parsec 3.0.0. Uploaded by Derek Elkins. [25]parsec: Monadic parser combinators. 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/estreps-0.1 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/clustertools-0.1 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xsact-1.6 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HsJudy-0.2 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/prof2dot-0.3.1 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/strict-0.3.2 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Emping-0.4 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GuiHaskell-0.1.1 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/simpleargs-0.1 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parsec-3.0.0 * hetris 0.2. Uploaded by Gwern Branwen. [26]hetris: Text Tetris. * hscurses 1.3. Uploaded by Gwern Branwen. [27]hscurses: NCurses bindings for Haskell. * photoname 2.0. Uploaded by Dino Morelli. [28]photoname: Rename JPEG photo files based on shoot date. * mage 1.1.0. Uploaded by Gwern Branwen. [29]mage: Rogue-like. * infix 0.1.1. Uploaded by Gwern Branwen. [30]infix: Infix expression re-parsing (for HsParser library). * bio 0.3.3. Uploaded by Gwern Branwen. [31]bio: A bioinformatics library. * dephd 0.0. Uploaded by Gwern Branwen. [32]dephd: Analyze 'phred' output (.phd files). * hybrid 2.0. Uploaded by Gwern Branwen. [33]hybrid: A implementation of a type-checker for Lambda-H. * propgrid 0.1. Uploaded by Gwern Branwen. [34]propgrid: GUI propertygrid. * gravatar 0.3. Uploaded by Donald Stewart. [35]gravatar: Find the url of the gravatar associated with an email address.. 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hetris-0.2 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hscurses-1.3 28. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/photoname-2.0 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mage-1.1.0 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/infix-0.1.1 31. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bio-0.3.3 32. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dephd-0.0 33. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hybrid-2.0 34. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/propgrid-0.1 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gravatar-0.3 * himerge 0.17.9. Uploaded by Luis Araujo. [36]himerge: Haskell Graphical User Interface for Emerge. * Takusen 0.8. Uploaded by Alistair Bayley. [37]Takusen: Database library with left-fold interface, for PostgreSQL, Oracle, SQLite, ODBC.. * irc 0.4.1. Uploaded by Trevor Elliott. [38]irc: A small library for parsing IRC messages.. * hexpat 0.2. Uploaded by Evan Martin. [39]hexpat: wrapper for expat, the fast XML parser. * microbench 0.1. Uploaded by Evan Martin. [40]microbench: Microbenchmark Haskell code. * hxt 7.5. Uploaded by Uwe Schmidt. [41]hxt: A collection of tools for processing XML with Haskell.. * hmatrix 0.2.1.0. Uploaded by Alberto Ruiz. [42]hmatrix: Linear algebra and numerical computations. * binary-strict 0.3.1. Uploaded by Adam Langley. [43]binary-strict: Binary deserialisation using strict ByteStrings. * category-extras 0.1. Uploaded by Dan Doel. [44]category-extras: Various modules and constructs inspired by category theory.. * pcap 0.4.3. Uploaded by Bryan OSullivan. [45]pcap: A system-independent interface for user-level packet capture. 36. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/himerge-0.17.9 37. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Takusen-0.8 38. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/irc-0.4.1 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hexpat-0.2 40. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/microbench-0.1 41. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hxt-7.5 42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix-0.2.1.0 43. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict-0.… 44. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/category-extras-… 45. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pcap-0.4.3 * curl 1.3.1. Uploaded by Eric Mertens. [46]curl: Haskell binding to libcurl. * fastcgi 3001.0.2. Uploaded by Bjorn Bringert. [47]fastcgi: A Haskell library for writing FastCGI programs. * hslogger 1.0.5. Uploaded by John Goerzen. [48]hslogger: Versatile logging framework. * HAppS-Server 0.9.2.1. Uploaded by David Himmelstrup. [49]HAppS-Server: Web related tools and services.. * HAppS-IxSet 0.9.2.1. Uploaded by David Himmelstrup. [50]HAppS-IxSet: Added by DavidHimmelstrup, Fri Feb 29 07:27:13 PST 2008.. * HAppS-State 0.9.2.1. Uploaded by David Himmelstrup. [51]HAppS-State: Event-based distributed state.. * HAppS-Data 0.9.2.1. Uploaded by David Himmelstrup. [52]HAppS-Data: HAppS data manipulation libraries. * HAppS-Util 0.9.2.1. Uploaded by David Himmelstrup. [53]HAppS-Util: Web framework. * sessions 2008.2.28. Uploaded by Matthew Sackman. [54]sessions: Session Types for Haskell. * utf8-string 0.3. Uploaded by Eric Mertens. [55]utf8-string: Support for reading and writing UTF8 Strings. 46. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl-1.3.1 47. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fastcgi-3001.0.2 48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hslogger-1.0.5 49. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Server-0.9… 50. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-IxSet-0.9.… 51. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-State-0.9.… 52. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Data-0.9.2… 53. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Util-0.9.2… 54. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions-2008.2.… 55. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/utf8-string-0.3 * EdisonCore 1.2.1.2. Uploaded by Robert Dockins. [56]EdisonCore: A library of efficent, purely-functional data structures (Core Implementations). * parameterized-data 0.1. Uploaded by Alfonso Acosta. [57]parameterized-data: Parameterized data library implementing lightweight dependent types. * unix 2.3.0.0. Uploaded by Ross Paterson. [58]unix: POSIX functionality. * hoogle 3.1. Uploaded by Neil Mitchell. [59]hoogle: Haskell API Search. * ftshell 0.2. Uploaded by Janis Voigtlaender. [60]ftshell: Shell interface to the FreeTheorems library.. * free-theorems 0.2. Uploaded by Janis Voigtlaender. [61]free-theorems: Automatic generation of free theorems.. * special-functors 1.0. Uploaded by Henning Thielemann. [62]special-functors: Control.Applicative, Data.Foldable, Data.Traversable (compatibility package). * type-level 0.1. Uploaded by Alfonso Acosta. [63]type-level: Type-level programming library. * nymphaea 0.2. Uploaded by Gwern Branwen. [64]nymphaea: An interactive GUI for manipulating L-systems. * hsc3 0.2. Uploaded by Rohan Drape. [65]hsc3: Haskell SuperCollider. 56. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/EdisonCore-1.2.1… 57. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parameterized-da… 58. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/unix-2.3.0.0 59. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle-3.1 60. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ftshell-0.2 61. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/free-theorems-0.2 62. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/special-functors… 63. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level-0.1 64. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/nymphaea-0.2 65. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsc3-0.2 * hosc 0.2. Uploaded by Rohan Drape. [66]hosc: Haskell Open Sound Control. * hslackbuilder 0.0.1. Uploaded by Andrea Rossato. [67]hslackbuilder: HSlackBuilder automatically generates slackBuild scripts from a cabal package. * hsparklines 0.1.0. Uploaded by Hitesh Jasani. [68]hsparklines: Sparklines for Haskell. * sat-micro-hs 0.1.1. Uploaded by Denis Bueno. [69]sat-micro-hs: A minimal SAT solver. * interlude 0.1.1. Uploaded by Gwern Branwen. [70]interlude: Replaces some Prelude functions for enhanced error reporting. * parse-dimacs 1.0.1. Uploaded by Denis Bueno. [71]parse-dimacs: DIMACS CNF parser library. * bitset 0.5. Uploaded by Denis Bueno. [72]bitset: A functional data structure for efficient membership testing.. * special-functors 1.0. Uploaded by Henning Thielemann. [73]special-functors: Control.Applicative, Data.Foldable, Data.Traversable (compatibility package). * condorcet 0.0.1. Uploaded by Gwern Branwen. [74]condorcet: Library for Condorcet voting. * heap 0.2.3. Uploaded by Stephan Friedrichs. [75]heap: Heaps in Haskell. 66. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hosc-0.2 67. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hslackbuilder-0.… 68. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsparklines-0.1.0 69. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sat-micro-hs-0.1… 70. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/interlude-0.1.1 71. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parse-dimacs-1.0… 72. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bitset-0.5 73. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/special-functors… 74. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/condorcet-0.0.1 75. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-0.2.3 * hspr-sh 0.3. Uploaded by Gwern Branwen. [76]hspr-sh: Session handler for HSP. * hsp 0.2. Uploaded by Gwern Branwen. [77]hsp: Haskell Server Pages is a library for writing dynamic server-side web pages.. * trhsx 0.2.1. Uploaded by Gwern Branwen. [78]trhsx: trhsx is the preprocessor for Harp and HSP. * haskell-src-exts 0.2.1. Uploaded by Gwern Branwen. [79]haskell-src-exts: Manipulating Haskell source: abstract syntax, lexer, parser, and pretty-printer. * harp 0.2.1. Uploaded by Gwern Branwen. [80]harp: HaRP allows pattern-matching with regular expressions. * HTF 0.1. Uploaded by Gwern Branwen. [81]HTF: The Haskell Test Framework. * hsdip 0.1. Uploaded by Gwern Branwen. [82]hsdip: hsdip - a Diplomacy parser/renderer. * mpdmate 0.1. Uploaded by Gwern Branwen. [83]mpdmate: MPD/PowerMate executable. * powermate 0.1. Uploaded by Gwern Branwen. [84]powermate: PowerMate bindings. * syb-with-class 0.4. Uploaded by David Himmelstrup. [85]syb-with-class: Scrap Your Boilerplate With Class. 76. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hspr-sh-0.3 77. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsp-0.2 78. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/trhsx-0.2.1 79. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… 80. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/harp-0.2.1 81. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTF-0.1 82. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsdip-0.1 83. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mpdmate-0.1 84. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/powermate-0.1 85. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/syb-with-class-0… * whim 0.1. Uploaded by Gwern Branwen. [86]whim: A Haskell window manager. * memcached 0.1. Uploaded by Gwern Branwen. [87]memcached: haskell bindings for memcached. * HaLeX 1.1. Uploaded by Gwern Branwen. [88]HaLeX: HaLeX enables modelling, manipulation and animation of regular languages. 86. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/whim-0.1 87. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/memcached-0.1 88. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HaLeX-1.1 Jobs Haskell for real-time control software. Tom Hawkins [89]announced an opening for a Haskell job in real-time control software for vehicle and machinery applications 89. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37093 Haskell for bioinformatics. Ketil Malde [90]announced an open position for a 3-year Ph.D. scolarship at IMR working on bioinformatics projects in Haskell 90. http://news.gmane.org/gmane.comp.lang.haskell.cafe/cutoff=37362 Blog noise [91]Haskell news from the [92]blogosphere. * [93]Barracuda P2P Chat * [94]A Lambda Calculus Reducer * [95]A Fashion Magazine in Haskell * [96]Introduction to building stateful web apps in HAppS * [97]Intro to HAppS-State * [98]Project Euler in Haskell * [99]In praise of mandatory indentation for novice programmers * [100]More Monads on the Cheap: Inlined fromMaybe * [101]A First Haskell Experience * [102]Haskell and code coverage * [103]Why I don't use Haskell for Functional Programming (monads, lifting) 91. http://planet.haskell.org/ 92. http://haskell.org/haskellwiki/Blog_articles 93. http://haskell.org/gtk2hs/archives/2008/02/24/barracuda-p2p-chat/ 94. http://www.defmacro.org/ramblings/lambda-reducer.html 95. http://www.alpheccar.org/en/posts/show/91 96. http://softwaresimply.blogspot.com/2008/02/intro-to-happs-part-1.html 97. http://softwaresimply.blogspot.com/2008/02/intro-to-happs-state.html 98. http://extempore.livejournal.com/212602.html 99. http://okasaki.blogspot.com/2008/02/in-praise-of-mandatory-indentation-for.… 100. http://osteele.com/archives/2008/02/inlined-frommaybe 101. http://the-programmers-stone.com/2008/03/04/a-first-haskell-experience/ 102. http://dukedave.blogspot.com/2008/03/back-in-action.html 103. http://jlouisramblings.blogspot.com/2008/03/why-i-dont-use-haskell-for-func… Quotes of the Week * teamonkey: the Haskell solutions that people are posting are generally so much more concise and elegant than for any other language * Dan Zwell: I am fairly new to Haskell, and I didn't realize how easy concurrent code is until I wrote this * anonymous: The Haskall (sic) language is often uses by very intelligent programmers, it often allows to use lazy computations and iterations, but it has the advantage that its iterators behave better (than in Python), and during the generation of some items you can, when you want, refer and use the items already generated. * Corun: I don't understand, what's the advantage of hugs? The uni here says to use hugs, though, but I kept finding myself going in to ghci to get a useful error message * They say that if it compiles, it will run correctly. It?s nearly true! I?m amazed. ... Such buglessness will remove a huge source of indeterminism in production environments where the work of many teams is co-ordinated by schedules. * dolio: I've made a domain specific notation for describing puddings. * cschneid: [Haskell] changed the way I look at decomposition of problems in the more corporate languages (Java and C#). I use far fewer variables, and more side-effect free methods. It's made my code clearer, and easier to test. * nicodemus: I've written some Erlang and much more Haskell. My take so far is that Erlang is good for teaching you how to fish, Haskell is good for teaching you about procuring food (including fish). * paulzork: Haskell is to functional programming like C is to imperative languages? Sort of the latin root? About the Haskell Weekly News New editions are posted to [104]the Haskell mailing list as well as to [105]the Haskell Sequence and [106]Planet Haskell. [107]RSS is also available, and headlines appear on [108]haskell.org. Headlines are available as [109]PDF. To help create new editions of this newsletter, please see the [110]contributing information. Send stories to dons at galois.com. The darcs repository is available at darcs get [111]http://code.haskell.org/~dons/code/hwn/ 104. http://www.haskell.org/mailman/listinfo/haskell 105. http://sequence.complete.org/ 106. http://planet.haskell.org/ 107. http://sequence.complete.org/node/feed 108. http://haskell.org/ 109. http://code.haskell.org/~dons/code/hwn/archives/20080309.pdf 110. http://haskell.org/haskellwiki/HWN 111. http://code.haskell.org/~dons/code/hwn/

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simple Haskell question - List comprehensions
by Philip Müller 09 Mar '08

09 Mar '08

Hi, I'm just working through Hutton's "Programming in Haskell" and I found an exercise which I can't solve, although it looks simple. Maybe someone here could give me a hint? Exercise: Show how the single comprehension [(x,y) | x <- [1,2,3], y <- [4,5,6]] with two generators can be re-expressed using two comprehensions with single generators. Hint: make use of the library function _concat_. Thank you very much, Philip

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deriving instances of Enum for tuples of bounded, enumerable types (useful for generating QuickCheck.Arbitrary instances for collection of collection types)
by Thomas Hartman 09 Mar '08

09 Mar '08

I have some code for creating instances of Enum for a tuple of bounded enumerable types. The main win with this was that it makes it easier for me to generate Test.QuickCheck.Arbitrary instances for types that are based on collections of enumerable collections -- like you might get when modeling poker for instance. In fact, I was trying to answer the question about using QuickCheck with poker, that Vincent Foley asked a few days ago at http://groups.google.com/group/fa.haskell/browse_thread/thread/8298c4d838c9… when I came up with this. (And I am posting a reply to Vincent right after I finish writing this message.) Basically I noticed that coming up with the Arbitrary instances seemed to be tricker than I would have expected. However, it was pretty straightforward to write an instance of arbitrary for instance (Enum a, Bounded a) => Arbitrary a where arbitrary = do n <- choose (fromEnum (minBound :: a), fromEnum (maxBound :: a) ) return $ toEnum n So all I needed to do was get my type into instances of Enum and Bounded, and I got my Arbitrary instance for free. Most of the work was just writing the instances for various tuples of Bounded Enumerable types. Maybe I've been spoiled by how easy many types are gotten using the magic of the deriving clause, but this seemed like a lot of work to me. I was wondering if there was an easier way? Or if not, if it would make sense for something like this to be added to the prelude? Or is there some sizeable collection of nice Arbitrary instances for QuickCheck somewheres that I can leverage off of, that hasn't made it into the standard libraries? A minor issue: I had a question if I could make the type signatures for Enum instances less verbose by doing something like type BoundedEnum = (Bounded a, Enum a) => a... I tried, and commented out my attempt as it wouldn't type check. Guidance appreciated. Thanks, Thomas. Code follows: {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-} module EnumInstances where -- instances of Enum for tuples of types that are both Bounded and Enum -- typechecks, and does the right thing, though this signature seems messy, specially when I -- want to do this kind of thing for longer tuples instance (Enum a, Enum b,Bounded a, Bounded b) => Enum (a,b) where fromEnum (primero,segundo) = ( divFactor * (fromEnum primero) ) + (fromEnum segundo) where divFactor = fromEnum (maxBound :: b) + 1 toEnum i | (i > (fromEnum (maxBound :: (a,b)))) || (i < (fromEnum (minBound :: (a,b)))) = error "Enum (a,b) bounds error" | otherwise = (a,b) where a = toEnum baseline b = toEnum $ i - (baseline * divFactor ) baseline = i `div` divFactor divFactor = (fromEnum (maxBound :: b)) + 1 -- I tried to use a type synonym to write a cleaner type syg but... type BoundedEnumerable = (Enum a, Bounded a) => a -- does not typecheck. oh well, the verbose signatures aren't all that bad. {- instance Enum (BoundedEnumerable,BoundedEnumerable) where fromEnum (primero,segundo) = ( divFactor * (fromEnum primero) ) + (fromEnum segundo) where divFactor = fromEnum (maxBound :: b) + 1 toEnum i | (i > (fromEnum (maxBound :: (a,b)))) || (i < (fromEnum (minBound :: (a,b)))) = error "Enum (a,b) bounds error" | otherwise = (a,b) where a = toEnum baseline b = toEnum $ i - (baseline * divFactor ) baseline = i `div` divFactor divFactor = (fromEnum (maxBound :: b)) + 1 -} instance (Enum t, Enum t1, Enum t2, Bounded t, Bounded t1, Bounded t2) => Enum (t,t1,t2) where fromEnum (a,b,c) = fromEnum ((a,b),c) toEnum i = (a,b,c) where ((a,b),c) = toEnum i instance (Enum t, Enum t1, Enum t2, Enum t3, Bounded t, Bounded t1, Bounded t2, Bounded t3) => Enum (t,t1,t2,t3) where fromEnum (a,b,c,d) = fromEnum ((a,b,c),d) toEnum i = (a,b,c,d) where ((a,b,c),d) = toEnum i instance (Enum t, Enum t1, Enum t2, Enum t3, Enum t4, Bounded t, Bounded t1, Bounded t2, Bounded t3, Bounded t4) => Enum (t,t1,t2,t3,t4) where fromEnum (a,b,c,d,e) = fromEnum ((a,b,c,d),e) toEnum i = (a,b,c,d,e) where ((a,b,c,d),e) = toEnum i

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c_open and c_close signatures in the unix package
by Galchin Vasili 09 Mar '08

09 Mar '08

Hello, I need to find the c_open and c_close signatures that are referenced in unix/System/Posix/IO.hsc. Thanks, Vasya

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reply to vincent foley's question about poker
by Thomas Hartman 08 Mar '08

08 Mar '08

Weirdly, I came across a question Vincent Foley asked in FA Haskell when I read it in the googlegroups interface, http://groups.google.com/group/fa.haskell/browse_thread/thread/8298c4d838c9… but I don't seem to have his question in my inbox where I get haskell cafe. Maybe it got filtered somehow? I notice nobody else from Haskell Cafe seems to have answered, and this is usually a pretty helpful place so I am thinking maybe it really did get filtered. Oh well, I will answer it anyway now.. The question had to do with writing Arbitrary instances for datatypes useful for playing poker, and using quickCheck with them. I like my solution because I get Arbitrary instances for basically every datatype that's involved, from a single definition that gives you Arbitrary for any type a that is both Enum and Bounded. instance (Enum a, Bounded a) => Arbitrary a where arbitrary = do n <- choose (fromEnum (minBound :: a), fromEnum (maxBound :: a) ) return $ toEnum n Here's the code. (Note: For the code to compile you need the EnumInstances .hs module. I posted this a few minutes ago on haskell cafe.) {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-} module Cards where import Test.QuickCheck import Control.Arrow import Debug.Trace import EnumInstances -- Types data Suit = Clubs | Diamond | Heart | Spade deriving (Show, Eq, Bounded, Enum, Ord) data Rank = Ace | Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Jack | Queen | King deriving (Show, Eq, Bounded, Enum,Ord) --instance Arbitrary Rank where -- arbitrary = return $ choose data Card = Card (Rank, Suit) deriving (Eq,Show,Bounded, Ord) instance Enum Card where fromEnum (Card (r,s)) = fromEnum (r,s) toEnum i = Card (toEnum i) -- to check a new instance with quickCheck -- quickCheck (pEnum :: SomeType -> Bool) pEnum x = x == (toEnum . fromEnum) x -- type Hand = [Card] -- a hand is five cards data Hand = Hand Card Card Card Card Card deriving (Eq,Show, Bounded) instance Enum Hand where fromEnum (Hand a b c d e) = fromEnum (a,b,c,d,e) toEnum i = Hand a b c d e where (a,b,c,d,e) = toEnum i instance (Enum a, Bounded a) => Arbitrary a where arbitrary = do n <- choose (fromEnum (minBound :: a), fromEnum (maxBound :: a) ) return $ toEnum n -- not a very useful property, and certainly fails -- but it proves we have a working Arbitrary instance for Hand. pHandIsAlwaysAceOfClubs h = h == (Hand c c c c c) where c = Card (Ace, Clubs) t1 = do quickCheck (pEnum :: Rank -> Bool) quickCheck (pEnum :: Suit -> Bool) quickCheck (pEnum :: Card -> Bool) quickCheck (pEnum :: Hand -> Bool) quickCheck pHandIsAlwaysAceOfClubs -- of course this fails traceIt x = trace (show x) x

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Difficulties implementing an incremental parser using Oleg-style left fold enumerator
by Johan Tibell 08 Mar '08

08 Mar '08

Dear haskell-cafe, I'm trying to write a parser combinator library with the following contraints: * Parses LL(1) grammars. * Is incremental i.e. it uses an Oleg style left fold enumerator to receive its input. * Is applicative but not monadic. The problem -- maybe there are others too -- is that when a parser such as many (byte 65) is run it will always return a 'Partial' result waiting for more input even though the enumerator is exhausted. In other words, there's no way to detect end of input. My current implementation of the parser type is newtype Parser r a = Parser { unParser :: S -> (a -> S -> Result r) -> (S -> Result r) -> Result r } where the first parameter is the parse state, the second a success continuation, and the third a failure continuation. The only tricky part (except for the above mentioned problem) is to implement the choice operator. I implement mine as instance Applicative (Parser r) where pure a = ... p <*> p' = Parser $ \s succ fail -> flip (unParser p s) fail $ \f s' -> unParser p' s' (succ . f) fail which I think is correct. Here follows my code. I hope someone has some idea how I could handle the end of input problem correctly. Thanks. -- Johan {-# LANGUAGE DeriveDataTypeable, Rank2Types #-} ----------------------------------------------------------------------------- -- | -- Module : Parsing.IParse -- Copyright : (c) Johan Tibell 2008 -- License : BSD3-style (see LICENSE) -- -- Maintainer : johan.tibell(a)gmail.com -- Stability : experimental -- Portability : portable -- -- An incremental LL(1) parser combinator library. -- ----------------------------------------------------------------------------- module Parsing.IParse ( -- * The 'Parser' type Parser, Enumerator, parse, -- * Primitive parsers satisfy, byte, module Control.Applicative ) where import Control.Applicative (Alternative(..), Applicative(..)) import Control.Monad (Functor(..)) import qualified Data.ByteString as S import Data.Int (Int64) import Data.Typeable (Typeable, showsTypeRep, typeOf) import Data.Word (Word8) import Prelude hiding (fail, succ) -- --------------------------------------------------------------------- -- The Parser type -- | The parse state. data S = S {-# UNPACK #-} !S.ByteString {-# UNPACK #-} !Int64 deriving Show -- | A parse either succeeds, fails or returns a suspension with which -- the parsing can be resumed. data Result a = Finished a S | Failed Int64 | Partial (S.ByteString -> Result a) deriving Typeable -- | For debug output. instance (Show a, Typeable a) => Show (Result a) where showsPrec d (Finished a s) = showParen (d > 10) showStr where showStr = showString "Finished " . showsPrec 11 a . showString " " . showsPrec 11 s showsPrec d (Failed pos) = showParen (d > 10) showStr where showStr = showString "Failed " . showsPrec 11 pos showsPrec d (Partial k) = showParen (d > 10) showStr where showStr = showString "Partial " . showsTypeRep (typeOf k) -- | A parser takes a parse state, a success continuation and a -- failure continuation and returns a 'Result'. newtype Parser r a = Parser { unParser :: S -> (a -> S -> Result r) -> (S -> Result r) -> Result r } -- --------------------------------------------------------------------- -- Instances instance Functor (Parser r) where fmap f p = Parser $ \s succ fail -> unParser p s (succ . f) fail instance Applicative (Parser r) where pure a = Parser $ \s succ _ -> succ a s p <*> p' = Parser $ \s succ fail -> flip (unParser p s) fail $ \f s' -> unParser p' s' (succ . f) fail instance Alternative (Parser r) where empty = Parser $ \s _ fail -> fail s p <|> p' = Parser $ \s@(S _ pos) succ fail -> unParser p s succ $ \s'@(S _ pos') -> if pos == pos' then unParser p' s' succ fail else fail s' -- --------------------------------------------------------------------- -- Running a parser -- | The initial, empty parse state. initState :: S initState = S S.empty 0 -- | This is the final continuation that turns a successful parse into -- a 'Result'. finishedCont :: a -> S -> Result a finishedCont v s = Finished v s -- | This is the final continuation that turns an unsuccessful parse -- into a 'Result'. failedCont :: S -> Result a failedCont (S _ pos) = Failed pos -- | A enumerator is a partially applied left fold over some -- 'S.ByteString' input. The caller supplies an initial seed and an -- iteratee function. The iteratee function returns @Left seed@ if it -- want to terminate the iteration early, otherwise @Right seed@. type Enumerator m s = (s -> S.ByteString -> Either s s) -> s -> m s -- | @parse p enumerator@ runs the parser @p@, pulling in new data -- using @enumerator@ when necessary, and return @Left pos@ on failure -- and @Right val remaining@ on success. parse :: Monad m => Parser r r -> (forall s. Enumerator m s) -> m (Either Int64 (r, S.ByteString)) parse p enumerator = -- First test if the parser can succeed without consuming any -- input. let seed = (unParser p) initState finishedCont failedCont in case seed of Failed pos -> return $ Left pos Finished x (S s _) -> return $ Right (x, s) _ -> -- Otherwise, use the enumerator to feed the parser some -- input. do (result, pos) <- enumerator iter (seed, 0) return $ case result of Failed pos' -> Left pos' Finished x (S s _) -> Right (x, s) Partial _ -> Left pos where iter (Partial k, pos) chunk = let pos' = pos + fromIntegral (S.length chunk) in case k chunk of partial@(Partial _) -> Right (partial, pos') result -> Left (result, pos') iter _ _ = error "Should be partial." -- --------------------------------------------------------------------- -- Primitive parsers -- | The parser @satisfy p@ succeeds for any character for which the -- supplied function @p@ returns 'True'. Returns the character that -- is actually parsed. satisfy :: (Word8 -> Bool) -> Parser r Word8 satisfy p = Parser $ \st@(S s pos) succ fail -> case S.uncons s of Just (b, bs) -> if p b then succ b (S bs (pos + 1)) else fail st Nothing -> Partial $ \s' -> unParser (satisfy p) (S s' pos) succ fail -- | @byte b@ parses a single byte @b@. Returns the parsed byte -- (i.e. @b@). byte :: Word8 -> Parser r Word8 byte b = satisfy (== b)

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[pdxfunc] pdxfunc meeting: Monday, March 10, 7pm, CubeSpace
by Justin Bailey 07 Mar '08

07 Mar '08

The Portland Functional Programming group is meeting again this Monday, March 10, at 7 p.m. Join us! ---------- Forwarded message ---------- From: Igal Koshevoy <igal(a)pragmaticraft.com> Date: Fri, Mar 7, 2008 at 11:26 AM Subject: [pdxfunc] pdxfunc meeting: Monday, March 10, 7pm, CubeSpace To: Igal Koshevoy <igal(a)pragmaticraft.com> Join us at the next meeting of pdxfunc, the Portland Functional Programming Study Group. We'll have presentations, demos and discussions. We welcome programmers interested in all functional languages and our meetings have content for coders of all skill levels. If interested, please also subscribe to our mailing list at http://groups.google.com/group/pdxfunc PRESENTATION * Dr. Bart Massey: Audio Processing With Haskell - Abstract: Dr. Massey will discuss and demonstrate a Haskell implementation of a WAVE file I/O library and compressor-limiter application that he's been working on. He'll also talk about why he chose Haskell to do this. - Speaker: Dr. Bart Massey teaches Computer Science at Portland State University, focusing on open source software engineering and artificial intelligence. He's the current Secretary of the X.org Board of Directors, co-author of the Nickle open source programming language, and spent many years as the faculty advisor the Portland State Aerospace Society that builds open source sounding rockets. REMAINDER We'll spend the rest of the meeting doing open discussion, talking about projects, technical challenges, recent developments, etc. It's a good group with a lot of varied experience, so there won't be any shortage of interesting discussion. NEWS Don Stewart, who gave the group's first presentation, recently announced that the Haskell-based xmonad tiling window manager he helps write is now one year old (http://www.haskell.org/pipermail/xmonad/2008-March/005021.html) and the "Real World Haskell" book that he, Bryan O'Sullivan and John Goerzen are writing has released some new draft chapters for previewing (http://book.realworldhaskell.org/) Congratulations, Don! Anyway, see you at the meeting! --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "pdxfunc" group. To post to this group, send email to pdxfunc(a)googlegroups.com To unsubscribe from this group, send email to pdxfunc-unsubscribe(a)googlegroups.com For more options, visit this group at http://groups.google.com/group/pdxfunc?hl=en -~----------~----~----~----~------~----~------~--~---

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Re: Data.HashTable
by gwern0＠gmail.com 07 Mar '08

07 Mar '08

On 2008.03.06 22:43:53 +0100, Johannes Waldmann <waldmann(a)imn.htwk-leipzig.de> scribbled 1.4K characters: > > In practice, Data.Map outperforms it in essentially all cases > > (Data.HashTable stops working beyond a certain size and so any > > asymptotic benefits, if they exist at all, don't have time to kick > > in). > > What! > > I learned at school, and I teach my students, > * balanced binary tree: costs are log(size) > * hashtable: cost are essentially constant > therefore, hashtable should be preferred in almost all cases > (if you know a reasonable hash function > and except where you need persistency, of course) > > the difference should be visible even for moderate sizes > (e.g. 1000). With a reasonable implementation I expect > log(1000) = 10 comparisons (and dereferencings) for the tree; > while the hashtable should have the computation of the hash value > (ideally, in registers), one memory access, and one comparison. > > ... but indeed some experiments with Data.Map and Data.Hashtable > support the point you made. That's either good for Data.Map > or bad for Data.Hashtable. > > PS: I did not manage to compile HsJudy-1.0 with ghc-6.8.2 > (some hsc file missing - perhaps that should be auto-generated? how?) > > Best regards, Johannes. Oh... I'm terribly sorry about that. It was I who uploaded HsJudy. The problem was, it's maintained by the Pugs project for some reason. The directory structure looks like: pugs/ thirdparty/ HsJudy/ hsregex/ HsSyck/ installed/ judy/ Judy-1.0.3/ Here Judy-1.0.3/ contains the actual C library Judy itself. So what the Cabalized package residing in HsJudy/ was doing was literally linking against stuff like '../judy/Judy-1.0.3/src/JudyL/*.o'. At the time I was packaging, Cabal didn't yet warn about problems like ../, so it would build and install just fine when I ran it with no problems; but I forgot that obviously all the ../ stuff would totally break in an sdist tarball. I think I've fixed it: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HsJudy-0.1.1>. -- gwern Air eavesdropping pipe-bomb TSCM Centro ^X JIC TWA USACIL Protection

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