February 2011 - Haskell

SLE 2011 - 2nd Call for papers
by João Fernandes 06 Feb '11

06 Feb '11

============================================================ 2nd CALL FOR PAPERS SLE 2011 4th International Conference on Software Language Engineering Braga, Portugal, 3-6 July 2011 http://planet-sl.org/sle2011/ Co-located with the 4th Summer School on Generative and Transformational Techniques in Software Engineering (GTTSE 2011) ============================================================= IMPORTANT DATES * 2011: Paper submission: April 08 (midnight Apia Samoa time) Author notification: May 13 Paper submission for online proceedings: June 17 Conference: July 03-06 Camera-ready copy submission for post-proceedings: August 29 --------------------------------------------------------- Software language engineering is devoted to topics related to artificial languages in software engineering. The foremost mission of the International Conference on Software Language Engineering (SLE) is to encourage and organize communication between communities that traditionally have looked at soft- ware languages from different, more specialized, and yet complementary perspectives. Thus, technologies, methods, experiments and case studies from modelware, grammarware, and ontologyware serving the objectives of software languages are of particular relevance to SLE. We invite high-quality submissions to all conference tracks. Submissions must be PDF files following the Springer LNCS style and will be managed using the EasyChair submission system. Please check the conference web site for further information. SLE 2011 will include a Doctoral Symposium that will provide a supportive yet questioning setting in which PhD students can present their work, including goals, methods, and preliminary results. The Symposium aims to provide students with useful guidance and feedback on various aspects of their research from established researchers and the other student attendees. Please forward this call to anyone who might be interested. http://planet-sl.org/sle2011/ --------------------------------------------------------- PAPER SUBMISSION Submitted papers must be original work and must not be previously published in, currently submitted to, or currently in consideration for any journal, book, conference, or workshop. Each submitted paper will be reviewed closely by at least three members of the program committee. Accepted papers will be distributed at the conference via the online proceedings as well as published in the post-proceedings, which will appear in the Springer Lecture Notes in Computer Science (LNCS) series. Authors will have the opportunity to revise their accepted paper(s) for the pre- and post- proceedings. For an accepted paper to appear in the proceedings, at least one author must attend the event and present the work. --------------------------------------------------------- RESEARCH PAPERS Research papers should report a substantial research contribution to SLE and/or a successful application of SLE techniques. We solicit high-quality contributions in the area of SLE ranging from theoretical and conceptual contributions to tools, techniques, and frameworks that support the aforementioned lifecycle activities. We list examples of tools, techniques, applications, and problems of interest to clarify the types of contributes that we seek: * Formalisms used in designing and specifying languages and tools that analyze such language descriptions * Language implementation techniques * Program and model transformation tools * Composition, integration, and mapping tools for managing different aspects of software languages or different manifestations of a given language * Transformations and transformation languages between languages and models * Language evolution * Approaches to elicitation, specification, or verification of requirements for software languages * Language development frameworks, methodologies, techniques, best practices, and tools for the broader language lifecycle covering phases such as analysis, testing , and documentation. * Design challenges in SLE * Applications of languages including innovative domain-specific languages or "little" languages The preceding list is neither exclusive nor exhaustive. Visit the conference web site for more information about the scope and topics of interest of SLE, or contact the program co-chairs with questions. Page limit: 20 --------------------------------------------------------- SHORT PAPERS Short papers may describe interesting or thought-provoking concepts that are not yet fully developed or evaluated, make an initial contribution to challenging research issues in SLE, or discuss and analyze controversial issues in the field. Page limit: 10 --------------------------------------------------------- TOOL DEMONSTRATION PAPERS Because of SLE's ample interest in tools, we seek papers that present software tools related to the field of SLE. These papers will accompany a tool demonstration to be given at the conference. The selection criteria include the originality of the tool, its innovative aspects, the relevance of the tool to SLE, and the maturity of the tool. Submissions may also include an appendix (that will not be published) containing additional screen-shots and discussion of the proposed demonstration. Page limit: 10 --------------------------------------------------------- MINI-TUTORIAL PAPERS SLE is composed of various research areas, such as grammarware, modelware, language schemas, and semantic technologies. The cross product of attendees at SLE creates a situation where the contribution from one session may be difficult to understand by those not initiated to the area. To help unite the various communities of SLE 2011, we solicit mini-tutorials that provide discussion points for mapping common ideas between related and complementary research topics of SLE. A mini-tutorial submission should be between 15 and 20 pages. --------------------------------------------------------- DOCTORAL SYMPOSIUM The Doctoral Symposium provides a forum for both early and late-stage PhD students to present their research and get detailed feedback and advice from researchers both in and out of their particular research area. Submissions are invited from PhD students working on any topic that falls within the SLE conference remit. Submissions consist of two parts, a research abstract and a letter of recommendation from the student's supervisor. See the upcoming Doctoral Symposium call for submissions for full details. Participants will also be invited to present a poster on their research as part of the conference poster session. ------------------------------------------------------------ GENERAL CHAIR João Saraiva Universidade do Minho, Portugal jas(a)di.uminho.pt PROGRAM CO-CHAIRS Uwe Aßmann Dresden University of Technology, Germany uwe.assmann(a)tu-dresden.de Anthony Sloane Macquarie University, Australia anthony.sloane(a)mq.edu.au DOCTORAL SYMPOSIUM CHAIRS Perdita Stevens University of Edinburgh, UK perdita.stevens(a)ed.ac.uk Eric Van Wyk University of Minnesota, USA evw(a)cs.umn.edu PROGRAM COMITTEE Adrian Johnstone, University of London, UK Aldo Gangemi, Semantic Technology Laboratory, Italy Alexander Serebrenik, Eindhoven University of Technology, Netherlands Ana Moreira, FCT/UNL, Portugal Anthony Cleve, University of Namur, Belgium Anya Helene Bagge, University of Bergen, Norway Bernhard Rumpe, Aachen University, Germany Bijan Parsia, University of Manchester, UK Brian Malloy, Clemson University, USA Bruno Oliveira, Seoul National University, Korea Chiara Ghidini, FBK-irst, Italy Daniel Oberle, SAP Research, Germany Eelco Visser, Delft University of Technology, Netherlands Eric Van Wyk, University of Minnesota, USA Fernando Pereira, Federal University of Minas Gerais, Brasil Fernando Silva Parreiras, University of Koblenz-Landau, Germany Friedrich Steimann, University of Hannover, Germany Görel Hedin, Lund University, USA Ivan Kurtev, University of Twente, Netherlands James Power, National University of Ireland, Ireland Jean-Marie Favre, OneTree Technologies, France Jeff Gray, University of Alabama, USA Jeff Z. Pan, University of Aberdeen, UK João Paulo Fernandes, Univ. of Minho& Univ. of Porto, Portugal John Boyland, University of Wisconsin-Milwaukee, USA John Grundy, Swinburne University of Technology, Australia Jordi Cabot, University of Toronto, Canada Jurgen Vinju, CWI, Netherlands Laurence Tratt, Middlesex University, UK Marjan Mernik, University of Maribor, Slovenia Mark van den Brand, Eindhoven University of Technology, Netherlands Michael Collard, University of Akron, USA Nicholas Kraft, University of Alabama, USA Paul Klint, CWI, Netherlands Paulo Borba, Federal University of Pernambuco, Brazil Peter Haase, University of Karlsruhe, Germany Peter Mosses, Swansea University, UK Ralf Möller, Hamburg University of Technology, Germany Silvana Castano, University of Milan, Italy Steffen Zschaler, Lancaster University, UK York Sure, University of Koblenz-Landau, Germany Zhenjiang Hu, National Institute of Informatics, Japan ORGANIZATION COMMITTEE José Creissac Campos (Finance Chair) Universidade do Minho, Portugal João Paulo Fernandes (Web and Publicity co-Chair) Universidade do Porto& Universidade do Minho, Portugal Jurgen Vinju (Workshop Selection Chair) CWI, The Netherlands Vadim Zaytsev (Publicity co-Chair) CWI, The Netherlands

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Polymorphic types in RHS of type instances
by Steven Keuchel 05 Feb '11

05 Feb '11

Hi list, I was wondering why GHC doesn't allow usage of polymorphic types in the right-hand side of type instance declarations for type families. The GHC user guide states: "The right-hand side of a type instance must be a monotype (i.e., it may not include foralls) [...]", but it doesn't state the reason. I stumbled upon this limitation when I was trying to generically calculate Johann's and Ghani's interpreter (transformers) for nested data types from their "Initial Algebra Semantics is Enough!" paper. Cheers, Steven

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[CFP] Continuation Workshop 2011
by oleg＠okmij.org 05 Feb '11

05 Feb '11

ACM SIGPLAN Continuation Workshop 2011 http://logic.cs.tsukuba.ac.jp/cw2011/ co-located with ICFP 2011, Tokyo, Japan Saturday, September 24, 2011 Call for Contributions Continuations have been discovered many times, which highlights their many applications in programming language semantics and program analysis, linguistics, logic, parallel processing, compilation and web programming. Recently, there has been a surge of interest specifically in delimited continuations: new implementations (in Scala, Ruby, OCaml, Haskell), new applications (to probabilistic programming, event-driven distributed processing), substructural and constructive logics, natural language semantics. The goal of the Continuation Workshop is to make continuations more accessible and useful -- to practitioners and to researchers in various areas of computer science and outside computer science. We wish to promote communication among the implementors and users in many fields. We would like to publicize the applications of continuations in academic (logic, linguistics) and practical fields and various programming languages (OCaml, Haskell, Scala, Ruby, Scheme, etc). Continuation Workshop 2011 will be informal. We aim at accessible presentations of exciting if not fully polished research, and of interesting academic, industrial and open-source applications that are new or unfamiliar. The workshop will have no published proceedings; submissions of short abstracts are preferred. We intend to organize a tutorial session on delimited continuations and their main applications, in the evening before the workshop, on Friday, September 23, 2011. Important dates --------------- Submission: June 25, 2011 Notification: August 8, 2011 Tutorials: September 23, 2011 Workshop: September 24, 2011 Format ------ The workshop will consist of presentations by the participants, selected from submitted abstracts. Participants are invited to submit working drafts, source code, and/or extended abstracts for distribution on the workshop homepage and to the attendees, but as the workshop will have no formal proceedings, any contributions may be submitted for publication to other venues. (See the SIGPLAN republication policy for more details.) Scope ----- We seek several types of presentations on topics related to continuations. We especially encourage presentations that describe work in progress, outline a future research agenda, or encourage lively discussion. Research presentations on: - implementations of continuations - semantics - type systems and logics - meta-theory and its mechanization - code generation with continuations or effects - distributed programming - systems programming and security - pearls Research presentations must be broadly accessible and should describe new ideas, experimental results, significant advances in the theory or application of continuations, or informed positions regarding new control operators. Application presentations, or status reports These broadly accessible presentations should describe interesting applications of continuations in research, industry or open source. We encourage presentations of applications from areas outside of programming language research -- such as linguistics, logics, AI, computer graphics, operating systems, etc. These presentations need not present original research, but should deliver information that is new or that is unfamiliar to the general ICFP audience. (A broadly accessible version of research presented elsewhere, with the most recent results and more discussion of future work may be acceptable as a CW 2011 status report.) The abstract submission should justify, to a general reader, why an application is interesting. Demos and work-in-progress reports Live demonstrations or presentations of preliminary results are intended to show new developments, interesting prototypes, or work in progress. In the abstract submission (which need only be about half a page), describe the demo and its technical content, and be sure to include the demo's title, authors, collaborators, references, and acknowledgments. A demonstration should take 10-15 minutes, and a work-in-progress report should take about 5 minutes. The exact time per demo will be decided based on the number of accepted submissions. (Presenters will have to bring all the software and hardware for their demonstration; the workshop organizers are only able to provide a projector.) Submission Guidelines and Instructions -------------------------------------- Unlike the previous Continuation Workshops, we do not require the submission of complete research papers. We will select presentations based on submitted abstracts, up to 2 (A4 or US letter) pages long in the PDF format (with the optional supplementary material, up to 8 PDF pages). Persons for whom this poses a hardship should contact the program chair. Submissions longer than a half a page should include a paragraph synopsis suitable for inclusion in the workshop program. Email submissions to cw2011-submit(a)logic.cs.tsukuba.ac.jp Organizers ---------- Yukiyoshi Kameyama, University of Tsukuba http://logic.cs.tsukuba.ac.jp/~kam/ Chung-chieh Shan, Rutgers University http://www.cs.rutgers.edu/~ccshan/ Oleg Kiselyov http://okmij.org/ftp/ Program Committee ----------------- Kenichi Asai, Ochanomizu University, Japan http://pllab.is.ocha.ac.jp/~asai/ Malgorzata Biernacka, University of Wroclaw, Poland http://www.ii.uni.wroc.pl/~mabi/ Hugo Herbelin, PPS - pi.r2, INRIA, France http://pauillac.inria.fr/~herbelin/index-eng.html Oleg Kiselyov http://okmij.org/ftp/ Julia Lawall, University of Copenhagen, Denmark http://www.diku.dk/~julia Tiark Rompf, EPFL, Switzerland Chung-chieh Shan, Rutgers University (Chair) http://www.cs.rutgers.edu/~ccshan/ Hayo Thielecke, University of Birmingham, UK http://www.cs.bham.ac.uk/~hxt

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a quick question
by Navin Rustagi 04 Feb '11

04 Feb '11

Hi all, I am stuck at a piece of code and am not able to figure out the error. uptable::[[Char]]->[([Char],Int,Int,Int,Int)]->[([Char],Int,Int,Int,Int)] uptable (xf:xs) main_array = map (\(x,y,z,r,t)-> do if x==xf then tupup x y z r t second xs ) main_array here tupup and second are functions which are working . When compiling this it gives the error Syntax error in expression (unexpected `)') I am not able to figure out where I could have gone wrong. I have tried all bracketing combinations and nothing works. Navin

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Haskell Functions Help
by Manolache Andrei-Ionut 03 Feb '11

03 Feb '11

I need help with two functions....first this is the curent code :http://pastebin.com/UPATJ0r ->Function 1)removeTautologies :: Formula->Formula If in a clause, a literal and its negation are found, it means that the clause will be true, regardless of the value finally assigned to that propositional variable. Consider the following example: (A v B v -A) ^ (B v C v A) The first clause contains the literals A and -A. This means that the clause will always be true, in which case it can be simplify the whole set to simply (B v C v A) . I was tinking of using something like removeTautologies (f:fs)=filter rTf:removeTautologies fs where rT-is supposed to take the firs Literal from the clasue and search for a similar one,if one si found we compare the values if not the we go to the second literal. ->Function 2)pureLiteralDeletion :: Formula->Formula This is a little bit complicate but from What I get this function is suppose to implement a simplification step that assumes as true any atom in a formula that appears exclusively in a positive or negative form (not both). Consider the formula: (P v Q v R) ^ (P v Q v -R) ^ (-Q v R) Note that in this formula P is present but -P is not. Using Pure Literal Deletion it can be assumed that the value of P will be True thus simplifying the formula to (-Q v R). If the literal were false then the literal would simply be deleted from the clauses it appears in. In that case any satisfying model for the resulting formula would also be a satisfying model for the formula when we assume that the literal is true.

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ANNOUNCE: Database Supported Haskell (DSH)
by George Giorgidze 03 Feb '11

03 Feb '11

I am pleased to announce that Database Supported Haskell (DSH) has been released on Hackage [1]. DSH is a Haskell library for database-supported program execution. Using this library a relational database management system (RDBMS) can be used as a coprocessor for the Haskell programming language, especially for those program fragments that carry out data-intensive and data-parallel computation. Database executable program fragments can be written using the list comprehension notation (with modest syntax changes due to quasiquoting) and list processing combinators from the Haskell list prelude. Note that rather than embedding a relational language into Haskell, we turn idiomatic Haskell programs into SQL queries. DSH faithfully represents list order and nesting, and compiles the list processing combinators into relational queries. The implementation avoids unnecessary data transfer and context switching between the database coprocessor and the Haskell runtime by ensuring that the number of generated relational queries is only determined by the program fragment's type and not by the database size. DSH can be used to allow existing Haskell programs to operate on large scale data (e.g., larger than the available heap) or query existing database resident data with Haskell. Note that this package is flagged experimental and therefore not suited for production use. This is a proof of concept implementation only. To learn more about DSH, our paper entitled as "Haskell boards the Ferry: Database-supported program execution for Haskell" is a recommended reading [2]. The package includes a couple of examples that demonstrate how to use DSH. [1] http://hackage.haskell.org/package/DSH [2] http://www-db.informatik.uni-tuebingen.de/files/publications/ferryhaskell.p…

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ANNOUNCE: time-1.2.0.4
by Ashley Yakeley 03 Feb '11

03 Feb '11

A small update, time-1.2.0.4 fixes a bug in parseTime reported to me by Michael Gurlitz: > import Data.Time > import Data.Time.Clock > import System.Locale > > main = print (parseTime defaultTimeLocale "%e %B %Y" "April 2000" :: > Maybe Day) > -- Just *** Exception: Prelude.read: no parse Specifically: > parseTime defaultTimeLocale "%e" "" :: Maybe Day > -- Just *** Exception: Prelude.read: no parse In time-1.2.0.4, they now correctly evaluate to Nothing. I've updated the unit tests to catch this too. -- Ashley Yakeley

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Haskell Weekly News: Issue 167 - February 02, 2011
by Daniel Santa Cruz 03 Feb '11

03 Feb '11

Welcome to issue 167 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of January 23 to 29, 2011. This week I've added a section which compiles a list of the top answers given in StackOverflow during the week. These seem to be of more interest to more experienced Haskell users than the newbie questions usually posted on the site. See what you think. Announcements R. Emre Basar [2]annouced the release of follower, a tool that allows you to follow people's tweets without having an account with Twitter. Alberto Ruiz [3]announced hmatrix version 0.11, a package for numerical computation based on LAPACK and SGL. Michael Snoyman [4]made some point updates for WAI and Warp. "They fix some documentation issues, add some status aliases, make it possible to handle exceptions more easily, and make things more responsive on Windows." Antoine Latter [5]announced a minor point release for Parsec 3.1.0. John Meacham [6]announced version 0.7.7 of jhc is out! "This release fixes a large number of bugs that cropped up when compiling haskell out in the wild as well as adds some more features. A major one being the garbage collector is enabled by default." Quotes of the Week * Twey: Maybe Bool: the Haskell equivalent to True/False/FileNotFound * elliott: Only two things in the universe are certain: Death, and two of the libraries you've decided to use taking different types of ByteString. * shapr: my personal heuristics judge Haskell as totally practical, perhaps too practical. * monochrom: the guys that I see when I look into the irc window believe that I'm just a bunch of text. * bernardh: Refactoring: spend a week to get where you were * Question: How do I use "fix", and how does it work? Answer (by TomMD): The prank answer is "fix has no real use, it's just there so you can type 'fix error' in ghci and feel good about yourself." Top Reddit Stories * Haskell at Bump Domain: devblog.bu.mp, Score: 44, Comments: 9 On Reddit: http://www.reddit.com/r/haskell/comments/f8cr8/haskell_at_bump/ Original: http://devblog.bu.mp/haskell-at-bump * How to write a simple TCP Server in Haskell Domain: catonmat.net, Score: 35, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/faa80/how_to_write_a_simple_tcp_se… Original: http://catonmat.net/blog/simple-haskell-tcp-server * Snap Framework article in IEEE Internet Computing Domain: steve.vinoski.net, Score: 32, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/fa0e0/snap_framework_article_in_ie… Original: http://steve.vinoski.net/blog/2011/01/21/column-on-the-snap-framework/ * My Dream GHCi Session, Take 2 Domain: cdsmith.wordpress.com, Score: 23, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/f8im5/my_dream_ghci_session_take_2/ Original: http://cdsmith.wordpress.com/2011/01/24/my-dream-ghci-session-take-2/ * Text: a visual programming language based on Haskell, demo Domain: vimeo.com, Score: 20, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/fbgxd/text_a_visual_programming_la… Original: http://vimeo.com/19273744 * Hoogle Embed Domain: neilmitchell.blogspot.com, Score: 16, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/f7iqa/hoogle_embed/ Original: http://neilmitchell.blogspot.com/2011/01/hoogle-embed.html * What does this mean for Haskell on Android? Domain: reddit.com, Score: 15, Comments: 12 On Reddit: http://www.reddit.com/r/haskell/comments/f9o67/what_does_this_mean_for_hask… Original: http://www.reddit.com/r/Android/comments/f97zh/google_not_happy_with_number… * Evolving a computer with Genprog (exercises from the TECS book) Domain: jpmoresmau.blogspot.com, Score: 13, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/f7y6a/evolving_a_computer_with_gen… Original: http://jpmoresmau.blogspot.com/2011/01/evolving-computer-with-tecs-and-genp… * All about MVars : Inside T5 Domain: blog.ezyang.com, Score: 13, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/fduxb/all_about_mvars_inside_t5/ Original: http://blog.ezyang.com/2011/02/all-about-mvars/ * What textbooks would be useful to start approaching the low-hanging fruit on the ghc project? Domain: self.haskell, Score: 12, Comments: 8 On Reddit: http://www.reddit.com/r/haskell/comments/f8dm5/what_textbooks_would_be_usef… Original: /r/haskell/comments/f8dm5/what_textbooks_would_be_useful_to_start/ Top StackOverflow Answers * What is an idiomatic way to add lists in Haskell? Votes: 14 Read on SO: http://stackoverflow.com/questions/4776750/what-is-an-idiomatic-way-to-add-… There is a zipWith library function that combines two lists by using a supplied function. It does exactly what you want here and you get: addLists = zipWith (+) This uses (+) to combine the elements of lists given as further arguments. * Why don't the Haskell standard libraries make more use of polymorphism? Votes: 15 Read on SO: http://stackoverflow.com/questions/4779028/why-dont-the-haskell-standard-li… There is a very good pragmatic reason that "standard" Haskell (Prelude + base + maybe some more) doesn't use more polymorphism: Designing general-use type classes is hard. Good designs for classes that abstract over container types like lists, arrays and "bytestrings" (personally I don't really consider Bytestring a container) aren't floating round waiting … * How do I use fix, and how does it work? Votes: 17 Read on SO: http://stackoverflow.com/questions/4787421/how-do-i-use-fix-and-how-does-it… You are doing nothing wrong. fix id is an infinite loop. When we say that fix returns the least fixed point of a function, we mean that in the domain theory sense. So fix (\x -> 2*x-1) is not going to return 1, because although 1 is a fixed point of that function, it is not the least one in the domain ordering. I can't describe the domain ordering in … Top StackOverflow Questions * Why don't the Haskell standard libraries make more use of polymorphism? votes: 20, answers: 4 Read on SO: http://stackoverflow.com/questions/4779028/why-dont-the-haskell-standard-li… * How do I use fix, and how does it work? votes: 11, answers: 3 Read on SO: http://stackoverflow.com/questions/4787421/how-do-i-use-fix-and-how-does-it… * Why wrapping the Data.Binary.Put monad creates a memory leak? votes: 11, answers: 2 Read on SO: http://stackoverflow.com/questions/4828902/why-wrapping-the-data-binary-put… * Is there any kind of statistical natural language processing library for Haskell? votes: 9, answers: 1 Read on SO: http://stackoverflow.com/questions/4808702/is-there-any-kind-of-statistical… * How do you structure a stateful module in Haskell? votes: 8, answers: 2 Read on SO: http://stackoverflow.com/questions/4785379/how-do-you-structure-a-stateful-… About the Haskell Weekly News You can find an html version of this newsletter at my blog: http://contemplatecode.blogspot.com/2011/02/haskell-weekly-news-issue-167.h… Special thanks to Jean-Philippe Gariepy for sending in a quote for this week's quotes! We need more eyes! To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/85566 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/85648 4. https://groups.google.com/d/topic/haskell-cafe/Yd2ADZzonSI/discussion 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/85761 6. https://groups.google.com/d/topic/fa.haskell/T6EM4jbhj8w/discussion

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