- Haskell-Cafe - Haskell.org

Haskell w/ delimited continuations
by oleg＠okmij.org 23 Feb '08

23 Feb '08

Call-by-name lambda-calculus is strictly more expressive (in Felleisen sense) than call-by-value lambda-calculus, and the call-by-need (aka, lazy) lambda-calculus is observationally equivalent to the call-by-name. One can add shift/reset to any of these calculi (CBV shift/reset is most known; there are several CBN shift/reset, including the one I'm particularly attached to; in principle one can add shift/reset to call-by-need). Adding control effects (shift/reset) changes the expressivity results. Now all three calculi are distinct and none subsumes the other. For example, the expression reset( (\x -> 1) (abort 2)) evaluates to 1 in call-by-name and evaluate to 2 in call-by-value. The expression reset ((\x -> x + x) (shift f f)) has the type int->int in call-by-need (it is a function \x -> x + x) and it has the type int->int->int in call-by-name (and it is the curried addition function). The fact that call-by-need is no longer observationally equivalent to call-by-name and sharing becomes observable is the most distressing. It disables many optimizations GHC is allowed to do. Types help: there are call-by-name calculi with shift/reset with effect typing; one can look at the type and see what control effect an expression may make. That will still permit GHC optimize pure expressions and leave effectful expressions as they are. Alas, that type system is complex and I don't think inference is decidable there due to the presence of subtyping (one must annotate at least some of the binders with types, in particular, the binders of shift). It seems the simplest solution is to confine shift/reset to a monad. Regarding purity: the obligatory reference is Amr Sabry. What is a Purely Functional Language? In J. Functional Programming, 8(1), 1-22, Jan. 1998. http://www.cs.indiana.edu/~sabry/papers/purelyFunctional.ps Please see the definition 4.7. As Matthias Blume said, a bit informally, evaluation of a pure expression should not depend on CBN or CBV or some other such strategy. By this definition, an expression that involves shift/reset is not pure, as the above examples demonstrate.

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Haskell Weekly News: February 23, 2008
by Don Stewart 23 Feb '08

23 Feb '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080223 Issue 70 - February 23, 2008 --------------------------------------------------------------------------- Welcome to issue 70 of HWN, a newsletter covering developments in the [1]Haskell community. One hundred unique new and updated libraries and applications in the past two weeks, including mutable arrays, compression, games, web frameworks, data structures, a file system, Haskell tools, concurrency, graphics, cryptography, systems administration, signal processing, new guis and several audio libraries 1. http://haskell.org/ Hackage New and updated libraries in [2]the Hackage library database. 2. http://hackage.haskell.org/ * ArrayRef 0.1.2. Uploaded by Gwern Branwen. [3]ArrayRef: Unboxed references, dynamic arrays and more. * zlib 0.4.0.4. Uploaded by Duncan Coutts. [4]zlib: Compression and decompression in the gzip and zlib formats. * hetris 0.1. Uploaded by Gwern Branwen. [5]hetris: Text Tetris. * bzlib 0.4.0.3. Uploaded by Duncan Coutts. [6]bzlib: Compression and decompression in the bzip2 format. * HAppS-Server 0.9.2. Uploaded by David Himmelstrup. [7]HAppS-Server: Web related tools and services.. * HAppS-State 0.9.2. Uploaded by David Himmelstrup. [8]HAppS-State: Event-based distributed state.. * HAppS-Data 0.9.2. Uploaded by David Himmelstrup. [9]HAppS-Data: HAppS data manipulation libraries. * HAppS-IxSet 0.9.2. Uploaded by David Himmelstrup. [10]HAppS-IxSet: Added by DavidHimmelstrup, Fri Feb 22 15:18:20 PST 2008.. * HAppS-Util 0.9.2. Uploaded by David Himmelstrup. [11]HAppS-Util: Web framework. * Ranged-sets 0.2.0. Uploaded by Paul Johnson. [12]Ranged-sets: Ranged sets for Haskell. 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ArrayRef-0.1.2 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zlib-0.4.0.4 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hetris-0.1 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bzlib-0.4.0.3 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Server-0.9… 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-State-0.9.2 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Data-0.9.2 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-IxSet-0.9.2 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Util-0.9.2 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Ranged-sets-0.2.0 * halfs 0.2. Uploaded by Gwern Branwen. [13]halfs: Haskell File System. * sessions 2008.2.22. Uploaded by Matthew Sackman. [14]sessions: Session Types for Haskell. * infix 0.1. Uploaded by Gwern Branwen. [15]infix: Infix expression re-parsing (for HsParser library). * reify 0.1. Uploaded by Gwern Branwen. [16]reify: Serialize data. * highWaterMark 0.1. Uploaded by Gwern Branwen. [17]highWaterMark: Memory usage statistics. * hinvaders 0.1. Uploaded by Gwern Branwen. [18]hinvaders: Space Invaders. * baskell 0.1. Uploaded by Gwern Branwen. [19]baskell: An interpreter for a small functional language. * control-event 0.2. Uploaded by Thomas DuBuisson. [20]control-event: Event scheduling system.. * nymphaea 0.1. Uploaded by Gwern Branwen. [21]nymphaea: An interactive GUI for manipulating L-systems. * hopenssl 1.0. Uploaded by Peter Simons. [22]hopenssl: FFI bindings to OpenSSL's EVP digest interface. 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/halfs-0.2 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions-2008.2.… 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/infix-0.1 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/reify-0.1 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/highWaterMark-0.1 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hinvaders-0.1 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/baskell-0.1 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/control-event-0.2 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/nymphaea-0.1 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hopenssl-1.0 * Monadius 0.91. Uploaded by Gwern Branwen. [23]Monadius: 2-D arcade scroller. * postmaster 0.1. Uploaded by Peter Simons. [24]postmaster: Postmaster ESMTP Server. * hsyslog 1.2. Uploaded by Peter Simons. [25]hsyslog: FFI interface to syslog(3) from POSIX.1-2001.. * hsemail 1.2. Uploaded by Peter Simons. [26]hsemail: Internet Message Parsers. * hsdns 1.3. Uploaded by Peter Simons. [27]hsdns: Asynchronous DNS Resolver. * funcmp 1.1. Uploaded by Peter Simons. [28]funcmp: Functional MetaPost. * streamproc 1.1. Uploaded by Peter Simons. [29]streamproc: Stream Processer Arrow. * pugs-HsSyck 0.41. Uploaded by Gwern Branwen. [30]pugs-HsSyck: Fast, lightweight YAML loader and dumper. * HsSyck 0.42. Uploaded by Gwern Branwen. [31]HsSyck: Fast, lightweight YAML loader and dumper. * mohws 0.1. Uploaded by Gwern Branwen. [32]mohws: Modular Haskell Web Server. 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Monadius-0.91 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/postmaster-0.1 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsyslog-1.2 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsemail-1.2 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsdns-1.3 28. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funcmp-1.1 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/streamproc-1.1 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pugs-HsSyck-0.41 31. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HsSyck-0.42 32. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mohws-0.1 * HsJudy 0.1. Uploaded by Gwern Branwen. [33]HsJudy: Judy bindings, and some nice APIs. * probability 0.2.1. Uploaded by Henning Thielemann. [34]probability: Probabilistic Functional Programming. * dsp 0.2.1. Uploaded by Henning Thielemann. [35]dsp: Haskell Digital Signal Processing. * pugs-hsregex 1.0. Uploaded by Gwern Branwen. [36]pugs-hsregex: Haskell PCRE binding. * ListLike 1.0.1. Uploaded by John Goerzen. [37]ListLike: Generic support for list-like structures. * SDL-gfx 0.5.2. Uploaded by David Himmelstrup. [38]SDL-gfx: Binding to libSDL_gfx. * SDL-ttf 0.5.2. Uploaded by David Himmelstrup. [39]SDL-ttf: Binding to libSDL_ttf. * SDL-mixer 0.5.2. Uploaded by David Himmelstrup. [40]SDL-mixer: Binding to libSDL_mixer. * SDL-image 0.5.2. Uploaded by David Himmelstrup. [41]SDL-image: Binding to libSDL_image. * SDL 0.5.2. Uploaded by David Himmelstrup. [42]SDL: Binding to libSDL. 33. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HsJudy-0.1 34. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/probability-0.2.1 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dsp-0.2.1 36. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pugs-hsregex-1.0 37. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ListLike-1.0.1 38. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL-gfx-0.5.2 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL-ttf-0.5.2 40. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL-mixer-0.5.2 41. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL-image-0.5.2 42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL-0.5.2 * DeepArrow 0.2. Uploaded by Conal Elliott. [43]DeepArrow: Arrows for "deep application". * GuiTV 0.4. Uploaded by Conal Elliott. [44]GuiTV: GUIs for Tangible Values. * Shellac-compatline 0.9. Uploaded by Robert Dockins. [45]Shellac-compatline: "compatline" backend module for Shellac. * WordNet 0.1.2. Uploaded by Max Rabkin. [46]WordNet: Haskell interface to the WordNet database. * lazyarray 0.1.3. Uploaded by Milan Straka. [47]lazyarray: Efficient implementation of lazy monolithic arrays (lazy in indexes).. * GenI 0.16.1. Uploaded by Eric Kow. [48]GenI: A natural language generator (specifically, an FB-LTAG surface realiser). * libGenI 0.16.1. Uploaded by Eric Kow. [49]libGenI: A natural language generator (specifically, an FB-LTAG surface realiser). * alsa-midi 0.3.1. Uploaded by Henning Thielemann. [50]alsa-midi: Bindings for the ALSA sequencer API (MIDI stuff). * midi 0.0.5. Uploaded by Henning Thielemann. [51]midi: Handling of MIDI messages and files. * event-list 0.0.6. Uploaded by Henning Thielemann. [52]event-list: Event lists with relative or absolute time stamps. 43. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DeepArrow-0.2 44. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GuiTV-0.4 45. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Shellac-compatli… 46. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/WordNet-0.1.2 47. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lazyarray-0.1.3 48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GenI-0.16.1 49. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/libGenI-0.16.1 50. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/alsa-midi-0.3.1 51. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/midi-0.0.5 52. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/event-list-0.0.6 * numeric-quest 0.1.1. Uploaded by Henning Thielemann. [53]numeric-quest: Math and quantum mechanics. * markov-chain 0.0.2. Uploaded by Henning Thielemann. [54]markov-chain: Markov Chains for generating random sequences with a user definable behaviour.. * hmp3 1.5.1. Uploaded by Don Stewart. [55]hmp3: An ncurses mp3 player written in Haskell. * TypeIlluminator 0.0. Uploaded by Gwern Branwen. [56]TypeIlluminator: TypeIlluminator is a prototype tool exploring debugging of type errors/. * Takusen 0.7. Uploaded by Don Stewart. [57]Takusen: Database library with left-fold interface, for PostgreSQL, Oracle, SQLite, ODBC.. * carray 0.1.2. Uploaded by Jed Brown. [58]carray: A C-compatible array library.. * jack 0.5. Uploaded by Henning Thielemann. [59]jack: Bindings for the JACK Audio Connection Kit. * non-negative 0.0.1. Uploaded by Henning Thielemann. [60]non-negative: Non-negative numbers. * RJson 0.3.3. Uploaded by Alex Drummond. [61]RJson: A reflective JSON serializer/parser.. * clevercss 0.1.1. Uploaded by Georg Brandl. [62]clevercss: A CSS preprocessor. 53. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/numeric-quest-0.… 54. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/markov-chain-0.0… 55. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmp3-1.5.1 56. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/TypeIlluminator-… 57. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Takusen-0.7 58. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/carray-0.1.2 59. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/jack-0.5 60. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/non-negative-0.0… 61. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/RJson-0.3.3 62. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/clevercss-0.1.1 * fft 0.1.1. Uploaded by Jed Brown. [63]fft: Bindings to the FFTW library.. * storable-complex 0.1. Uploaded by Jed Brown. [64]storable-complex: Storable instance for Complex. * winerror 0.1. Uploaded by Felix Martini. [65]winerror: Error handling for foreign calls to the Windows API.. * linkchk 0.0.2. Uploaded by Gwern Branwen. [66]linkchk: linkchk is a network interface link ping monitor.. * popenhs 1.0.0. Uploaded by Gwern Branwen. [67]popenhs: popenhs is a popen-like library for Haskell.. * Flippi 0.0.3. Uploaded by Gwern Branwen. [68]Flippi: Wiki. * DisTract 0.2.5. Uploaded by Gwern Branwen. [69]DisTract: Distributed Bug Tracking System. * goa 3.0. Uploaded by Gwern Branwen. [70]goa: GHCi bindings to lambdabot. * hinstaller 2008.2.16. Uploaded by Gwern Branwen. [71]hinstaller: Installer wrapper for Haskell applications. * GeoIp 0.1. Uploaded by Stephen Cook. [72]GeoIp: Pure bindings for the MaxMind IP database.. 63. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fft-0.1.1 64. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/storable-complex… 65. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/winerror-0.1 66. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/linkchk-0.0.2 67. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/popenhs-1.0.0 68. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Flippi-0.0.3 69. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DisTract-0.2.5 70. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/goa-3.0 71. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hinstaller-2008.… 72. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GeoIp-0.1 * hpodder 1.1.2. Uploaded by John Goerzen. [73]hpodder: Podcast Aggregator (downloader). * wxcore 0.10.2. Uploaded by Eric Kow. [74]wxcore: wxHaskell core. * wx 0.10.2. Uploaded by Eric Kow. [75]wx: wxHaskell. * flow2dot 0.3. Uploaded by Dmitry Astapov. [76]flow2dot: Generates sequence diagrams from textual descriptions. * strict-concurrency 0.2. Uploaded by Donald Stewart. [77]strict-concurrency: Strict concurrency abstractions. * TV 0.4. Uploaded by Conal Elliott. [78]TV: Tangible Values -- composable interfaces. * geniconvert 0.15. Uploaded by Eric Kow. [79]geniconvert: Conversion utility for the GenI generator. * ctemplate 0.1. Uploaded by Adam Langley. [80]ctemplate: Binding to the Google ctemplate library. * arrows 0.4. Uploaded by Ross Paterson. [81]arrows: Arrow classes and transformers. * lhs2tex 1.13. Uploaded by Andres Loeh. [82]lhs2tex: Preprocessor for typesetting Haskell sources with LaTeX. 73. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hpodder-1.1.2 74. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wxcore-0.10.2 75. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wx-0.10.2 76. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/flow2dot-0.3 77. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/strict-concurren… 78. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/TV-0.4 79. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/geniconvert-0.15 80. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ctemplate-0.1 81. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/arrows-0.4 82. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lhs2tex-1.13 * NGrams 1.1. Uploaded by Justin Bailey. [83]NGrams: Simple application for calculating n-grams using Google.. * lambdabot 4.1. Uploaded by Gwern Branwen. [84]lambdabot: A multi-talented IRC bot. * HsOpenSSL 0.4. Uploaded by Masatake Daimon. [85]HsOpenSSL: (Part of) OpenSSL binding for Haskell. * network-minihttp 0.1. Uploaded by Adam Langley. [86]network-minihttp: A very minimal webserver. * ZFS 0.0. Uploaded by Gwern Branwen. [87]ZFS: Oleg's Zipper FS. * fst 0.9. Uploaded by Gwern Branwen. [88]fst: Finite state transducers. * haskell-in-space 0.1. Uploaded by Gwern Branwen. [89]haskell-in-space: 'Asteroids' arcade games.. * unix-pty-light 0.1. Uploaded by Stuart Cook. [90]unix-pty-light: POSIX pseudo-terminal support. * bot 0.1. Uploaded by Conal Elliott. [91]bot: bots for functional reactive programming. * Hedi 0.1. Uploaded by Paolo Veronelli. [92]Hedi: Line oriented editor. 83. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/NGrams-1.1 84. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lambdabot-4.1 85. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HsOpenSSL-0.4 86. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-minihttp… 87. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ZFS-0.0 88. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fst-0.9 89. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-in-space… 90. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/unix-pty-light-0… 91. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bot-0.1 92. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hedi-0.1 * network-bytestring 0.1.1.2. Uploaded by Johan Tibell. [93]network-bytestring: Fast and memory efficient low-level networking. * leksah 0.1.1. Uploaded by Juergen NicklischFranken. [94]leksah: Haskell IDE written in Haskell. * nano-hmac 0.2.0. Uploaded by Hitesh Jasani. [95]nano-hmac: Bindings to OpenSSL HMAC.. * monadenv 0.0-2005-02-14. Uploaded by Gwern Branwen. [96]monadenv: Added by GwernBranwen, Sun Feb 10 20:15:11 PST 2008.. * blockio 0.0-2006-02-03. Uploaded by Gwern Branwen. [97]blockio: Block-oriented I/O Driver. * child 0.0-2005-02-14. Uploaded by Gwern Branwen. [98]child: Added by GwernBranwen, Sun Feb 10 19:35:20 PST 2008.. * highlighting-kate 0.2.1. Uploaded by John MacFarlane. [99]highlighting-kate: Syntax highlighting. 93. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-bytestri… 94. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/leksah-0.1.1 95. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/nano-hmac-0.2.0 96. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/monadenv-0.0-200… 97. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blockio-0.0-2006… 98. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/child-0.0-2005-0… 99. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/highlighting-kat… Blog noise [100]Haskell news from the [101]blogosphere. 100. http://planet.haskell.org/ 101. http://haskell.org/haskellwiki/Blog_articles * [102]Unit testing is not a substitute for static typing * [103]Misunderstandings about Erlang (and functional programming) * [104]Simple UNIX tools in OCaml * [105]The Evolution of the Imperative Programmer * [106]Onageristic speculation * [107]Rotating args in Haskell and Ruby block style programming * [108]Terse and verbose variable names in Haskell * [109]Pysec: Monadic Combinatoric Parsing in Python (aka Parsec in Python) * [110]Haskell and C structures 102. http://pinderkent.blogsavy.com/archives/154 103. http://tim-watson.blogspot.com/2008/02/ok-so-there-seem-to-be-few.html 104. http://fhtr.blogspot.com/2008/02/simple-unix-tools-in-ocaml.html 105. http://matburt.net/?p=33 106. http://pozorvlak.livejournal.com/91293.html 107. http://www.jasani.org/2008/02/rotating-args-in-haskell-and-ruby-block.html 108. http://www.dougalstanton.net/blog/index.php/2008/02/12/measuring-the-challe… 109. http://www.valuedlessons.com/2008/02/pysec-monadic-combinatoric-parsing-in.… 110. http://therning.org/magnus/archives/315 * [111]Haskell on Windows * [112]Haskell, HDBC and Sqlite * [113]Parsec and zippers for interpreters * [114]Playing with monad transformers * [115]Code CAN be beautiful * [116]Elegance and Power * [117]Why don't you use Haskell? * [118]Functional control flow * [119]Programs as functions and how I/O can fit in nicely * [120]Elegance and power 111. http://therning.org/magnus/archives/338 112. http://www.jasani.org/2008/02/haskell-hdbc-and-sqlite.html 113. http://sabbatical-year.blogspot.com/2008/01/brainfuck-its-last-one-i-promis… 114. http://sabbatical-year.blogspot.com/2008/02/playing-with-monad-transformers… 115. http://basildoncoder.com/blog/2008/02/22/code-can-be-beautiful/ 116. http://research.swtch.com/2008/02/elegance-and-power.html 117. http://reddit.com/info/69jbs/comments/ 118. http://neilmitchell.blogspot.com/2008/01/functional-flow-control.html 119. http://qplqyer.wordpress.com/2008/02/23/programs-as-functions-and-how-io-ca… 120. http://research.swtch.com/2008/02/elegance-and-power.html * [121]How important is elegance? * [122]Types, named (was: 'Name that type!'), plus two more questions * [123]Code CAN Be Beautiful * [124]True unions * [125]The craft of functional programming :: review 121. http://progjournal.blogspot.com/2008/02/how-important-is-elegance.html 122. http://blog.jbapple.com/2008/02/types-named-was-name-that-type-plus-two.html 123. http://basildoncoder.com/blog/2008/02/22/code-can-be-beautiful/ 124. http://calculist.blogspot.com/2008/02/true-unions.html 125. http://clipboarded.blogspot.com/2008/02/craft-of-functional-programming-rev… Quotes of the Week * Erik Engbrecht: The key to language success is making it powerful enough for a couple cowboys to do the work of an entire team in a shorter period of time. Selling fast and cheap is easy. If you have enough fast and cheap, the business people won't care if you are making it out of bubble-gum and duct-tape, because you are giving them what they want. * pozorvlak: I'm going to make what should be an uncontroversial statement: if you don't understand and use monads, you are at best a quarter of a Haskell programmer. A corollary of this is that, since using monad transformers is the only (or at least the approved) way to use two or more monads together, if you don't understand and use monad transformers you are at best half a Haskell programmer. * mrevelle: As Lisp to lists and Smalltalk to objects: Haskell to computation * Paul: I would use Haskell to build a product or service, and I mean that in the sense that I can see how to train a team and build processes (prototyping, implementation, quality, deployment, support) around Haskell. * Yegge: Haskell, OCaml and their ilk are part of a 45-year-old static-typing movement within academia to try to force people to model everything. About the Haskell Weekly News New editions are posted to [126]the Haskell mailing list as well as to [127]the Haskell Sequence and [128]Planet Haskell. [129]RSS is also available, and headlines appear on [130]haskell.org. Headlines are available as [131]PDF. To help create new editions of this newsletter, please see the [132]contributing information. Send stories to dons at galois.com. The darcs repository is available at darcs get [133]http://code.haskell.org/~dons/code/hwn/ 126. http://www.haskell.org/mailman/listinfo/haskell 127. http://sequence.complete.org/ 128. http://planet.haskell.org/ 129. http://sequence.complete.org/node/feed 130. http://haskell.org/ 131. http://code.haskell.org/~dons/code/hwn/archives/20080223.pdf 132. http://haskell.org/haskellwiki/HWN 133. http://code.haskell.org/~dons/code/hwn/

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A beginners question
by Harri Kiiskinen 23 Feb '08

23 Feb '08

Dear All, banging my head against Haskell, but liking the feeling of hurting brains. Just a simple question: If fmap (^4) [1,2,3] >>= \i -> shows i " " gives "1 16 81 " then why does let i = fmap (^4) [1,2,3] in shows i " " give "[1,16,81] " Probably very simple, but there must be a delicate difference between these two expressions. I just don't get it. -- Harri Kiiskinen <harri.kiiskinen(a)utu.fi>

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Re: [Haskell] *** JOB OFFER *** [...]
by Paul Johnson 23 Feb '08

23 Feb '08

Peter Verswyvelen wrote: > > PS: This job offer was already placed in the Haskell Café a while ago, > but I was advised there to place it in the main Haskell list. I hope > this is not considered as spam. > I certainly don't see it as spam. One day there will be a dozen jobs for Haskell programmers on Monster or Jobserve, and at that point another such announcement *would* be spam. But at the moment it has rarity value. Paul.

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Database relations mapping
by Radosław Grzanka 23 Feb '08

23 Feb '08

Hi, I'm developing toy application to learn HDBC. I have "problem" with doing relations mapping. Actually I don't know is it a problem or "feature". ;) Anyway, I have two tables with relation between them: (this example is simplified to the whole structure of database, you can imagine) CREATE TABLE TD_set ( setId INTEGER PRIMARY KEY, setName TEXT NOT NULL ) CREATE TABLE TO_card ( cardId INTEGER PRIMARY KEY AUTOINCREMENT, setId INTEGER NOT NULL," -- Relation to TD_set setSeq INTEGER NOT NULL ) (no foreign key as sqlite3 does not care anyway - at least AFAIK) And in Haskell: > type CardSet = String > > data Card = Card { > set :: CardSet, > seqNo :: Integer, > } There is no problem with filling the structure Card with "seqNo" but I can't fill "set". I would have to put there IO (CardSet) but I don't want to do that as whole structure returned from my mapping function is already inside IO monad. Can I do it? Here is my (perfect) function - http://hpaste.org/5839 . See "getCards" and some helper functions. This does not compile as (I believe) getElement wants to return IO (CardSet) Thank you in advance for all your input. Radek.

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Haskell w/ delimited continuations
by Taral 23 Feb '08

23 Feb '08

My understanding of these things is limited, but what would stop me, theoretically speaking, of making a version of ghc with these primitives added: type Prompt r reset :: (Prompt r -> r) -> r shift :: Prompt r -> ((a -> _) -> r) -> a (Where _ is either r or forall b. b) -- Taral <taralx(a)gmail.com> "Please let me know if there's any further trouble I can give you." -- Unknown

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haddock as a markdown preprocessor
by Conal Elliott 23 Feb '08

23 Feb '08

There was a chat today on #haskell<http://tunes.org/%7Enef/logs/haskell/08.02.20> (15:08 to 16:10) about evolving haddock. I'd like to get comments. The goal is to get the full functionality of a general purpose, programmer-friendly markup language like markdown. One example is image embedding. Another is friendly links (no visible URL). The idea is to make a future haddock be a *preprocessor* that generates pandoc's extended markdown (or some such). Documentation would be mostly markdown, with very few extensions for code documentation ('foo' and " Foo.Bar", maybe a bit more). Most of the doc would simply be passed through untouched. The code-doc extensions would get rewritten into standard markdown and mixed in with the rest. Pandoc could then take the generated markdown and produce HTML, LaTeX, DocBoook XML, etc. Perhaps there will be ways in which markdown falls short in expressiveness. If so, I'm guessing the shortcomings wouldn't be specific to the task of code documentation, and so could be approached as improvements to markdown/pandoc (which is written in Haskell). Since the old and new doc languages would be quite incompatible, we might want to specify in a .cabal file which language to use. Reactions? - Conal

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Re: [Haskell] Re: Re: RE: Extensible records: Static duck typing
by Mark P Jones 23 Feb '08

23 Feb '08

[Redirecting to haskell-cafe] Ben Franksen wrote: > TREX seems to be generally agreed to be too complicated to implement and > explain. What evidence do you have for this? Speaking as somebody who implemented Trex for Hugs (and who also witnessed Ben Gaster build an independent implementation), I'd have to disagree about the first part of this. As I recall, the implementation was reasonably straightforward, and wasn't any more complicated than other common type system extensions that I've worked on. I'm also not sure why you think it is complicated to explain, but I suppose that's even more subjective. One of the most difficult things about the Trex implementation was finding a syntax that meshed nicely with the rest of the Haskell syntax. This is likely to be a problem for any record system extension of Haskell---unless you're prepared to accept a more unconventional syntax---because many of the symbols that you might want to use ({, }, ., |, \, for example) have already been adopted for other purposes. Ah, syntax! All the best, Mark

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Support for Transaction Memory by Sun Microsystems ..
by Galchin Vasili 22 Feb '08

22 Feb '08

Hello, Found this: http://www.theregister.co.uk/2007/08/21/sun_transactional_memory_rock/ http://research.sun.com/spotlight/2007/2007-08-13_transactional_memory.html vasya

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Fwd: [Haskell-cafe] Repeated function application
by Thomas Hartman 22 Feb '08

22 Feb '08

This was easier for me to understand when written so, with the start value explicit times3 :: (a -> a) -> Int -> (a -> a) times3 f n !start | n == 0 = start | otherwise = times3 f (n-1) (f start) -- no stack overflow :) tTimes3 = times3 (+1) 1000000 0 Here, only the third arg, the start value, needs to be "bangified/strictified", and it's pretty clear why. Without the bang pattern, it stack overflows. What I'm not sure of is whether this version is in fact completely equivalent to Dan's version above. I hope it is. 2008/2/21, Dan Weston <westondan(a)imageworks.com>: > Ben Butler-Cole wrote: > > Hello > > > > I was surprised to be unable to find anything like this in the standard libraries: > > > > times :: (a -> a) -> Int -> (a -> a) > > times f 0 = id > > times f n = f . (times f (n-1)) > > > > Am I missing something more general which would allow me to repeatedly apply a function to an input? Or is this not useful? > > > Invariably, this seems to invite a stack overflow when I try this (and > is usually much slower anyway). Unless f is conditionally lazy, f^n and > f will have the same strictness, so there is no point in keeping nested > thunks. > > If you apply f immediately to x, there is no stack explosion and faster > runtime: > > > times :: (a -> a) -> Int -> (a -> a) > > times f !n !x | n > 0 = times f (n-1) (f x) > | otherwise = x > > > Dan > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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