- Haskell-Cafe - Haskell.org

TH splicing and recompilation checking
by Johannes Waldmann 16 Jul '13

16 Jul '13

Hi. we are using template Haskell to splice in some code that is produced by reading and transforming the contents of another file. now, if this "other file" is touched (by editing), but not the main file, then ghc (and cabal) do not realize that the main file does need to be recompiled. is there a way to tell them about the dependency? (example main file: https://github.com/apunktbau/co4/blob/master/CO4/Test/Queens.hs) - J.W.

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Call for Papers IFL 2013
by publicityifl＠gmail.com 16 Jul '13

16 Jul '13

Hello, Please, find below the third call for papers for IFL 2013. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL CALL FOR PAPERS 25th SYMPOSIUM ON IMPLEMENTATION AND APPLICATION OF FUNCTIONAL LANGUAGES - IFL 2013 RADBOUD UNIVERSITY NIJMEGEN, THE NETHERLANDS ACM In-Cooperation / ACM SIGPLAN AUGUST 28 - 30 2013 "Landgoed Holthurnsche Hof" http://ifl2013.cs.ru.nl We are proud to announce that the 25th edition of the IFL series returns to its roots at the Radboud University Nijmegen in the Netherlands. The symposium is held from 28th to 30th of August 2013. Scope ----- The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2013 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Following the IFL tradition, IFL 2013 will use a post-symposium review process to produce the formal proceedings which will be published in the ACM Digital Library. All participants of IFL 2013 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. Hence, publications that appear only in the draft proceedings do not count as publication for the ACM SIGPLAN republication policy. After the symposium, authors will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal review process. From the revised submissions, the program committee will select papers for the formal proceedings considering their correctness, novelty, originality, relevance, significance, and clarity. Invited Speaker --------------- Lennart Augustsson, currently employed by the Standard Chartered Bank, well-known for his work on Haskell, parallel Haskell, Cayenne, and Bluespec, is the invited speaker of IFL 2013. He will be talking about practical applications of functional programming. Submission Details ------------------ Submission deadline draft papers: July 31 Notification of acceptance for presentation: August 2 Early registration deadline: August 7 Late registration deadline: August 14 Submission deadline for pre-symposium proceedings: August 21 25th IFL Symposium: August 28-30 Submission deadline for post-symposium proceedings: November 11 Notification of acceptance for post-symposium proceedings: December 18 Camera-ready version for post-symposium proceedings: February 3 2014 Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English. Papers must adhere to the standard ACM two columns conference format. For the pre-symposium proceedings we adopt a 'weak' page limit of 12 pages. For the post-symposium proceedings the page limit of 12 pages is firm. A suitable document template for LaTeX can be found at: http://www.acm.org/sigs/sigplan/authorInformation.htm Papers are to be submitted via the conference's EasyChair submission page: https://www.easychair.org/conferences/?conf=ifl2013 Topics ------ IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools in the context of functional programming. If you are not sure whether your work is appropriate for IFL 2013, please contact the PC chair at rinus(a)cs.ru.nl. Topics of interest include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications Peter Landin Prize ------------------ The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Programme committee ------------------- - Thomas Arts, Quviq, Gothenburg, Sweden - Andrew Butterfield, Trinity College, Dublin, Ireland - Edwin Brady, University of St. Andrews, UK - Clemens Grelck, University of Amsterdam, Netherlands - Adam Granicz, IntelliFactory, Budapest, Hungary - Jeremy Gibbons, University of Oxford, UK - Fritz Henglein, University of Copenhagen, Denmark - Stephan Herhut, Intel Labs, Santa Clara, US - Ralf Hinze (co-chair), University of Oxford, UK - Zoltan Horvath, Eotvos Lorand University, Budapest, Hungary - Zhenjiang Hu, University of Tokyo, Japan - Mauro Jaskelioff, Universidad Nacional de Rosario, Argentina - Johan Jeuring, University of Utrecht, Netherlands - Rita Loogen, University of Marburg, Germany - Marco T. Morazan, Seton Hall University, New Jersey, US - Dominic Orchard, University of Cambridge, UK - Rinus Plasmeijer (chair), Radboud University Nijmegen, Netherlands - Tim Sheard, Portland State University, US - Sam Tobin-Hochstadt, Northeastern University / Indiana University, US - Peter Thiemann, University of Freiburg, Germany - Simon Thompson, University of Kent, UK Venue ----- The 25th IFL is organized by the Radboud University Nijmegen, Model Based Software Development Department at the Nijmegen Institute for Computing and Information Sciences. The event is held in the Landgoed Holthurnsche Hof, a rural estate in the woodlands surrounding Nijmegen. It can be reached quickly and easily by public transport.

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What does it mean to derive "equations of restricted from" in Haskell?
by Daryoush Mehrtash 16 Jul '13

16 Jul '13

In John Hughes's "The Design of Pretty printing library" paper, he says: "The implementations which we are trying to derive consist of equations of > a restricted form. We will derive implementations by proving their > constituent equations from the specification. By itself this is no > guarantee that the implemented functions satisfy the specification because > we might not have proved enough equation But if we also check that the > derived definitions are terminating and exhaustive then this property is > guaranteed" What does "restricted form" mean? What is the meaning and significance of "definitions are terminating and exhaustive"? -- Daryoush Weblog: http://onfp.blogspot.com/

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partially indeterminate?
by Christopher Howard 16 Jul '13

16 Jul '13

Hi. For learning, I was doing the "phone words" problem, where a function translates the digits of a phone number into all possible words. I am trying to connect this idea to the idea of list comprehensions / list monads (sort of the same thing, yes?) I know it is easy to do this: w = do two <- "ABC" three <- "DEF" four <- "GHI" -- and the other digits [[two, three, two, four]] -- for example But what if you don't know in advance what the digits will be? I'm not sure how to insert that deterministic component into this idea. So far, I have a framework like so: p dx = do undefined where m = map (\d -> case d of 2 -> "ABC" 3 -> "DEF" 4 -> "GHI" 5 -> "JKL" 6 -> "MNO" 7 -> "PRS" 8 -> "TUV" 9 -> "WXY" otherwise -> show d) dx I would appreciate any guidance.

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Re: [Haskell-cafe] Non-recursive let [Was: GHC bug? Let with guards loops]
by oleg＠okmij.org 16 Jul '13

16 Jul '13

I'd like to emphasize that there is a precedent to non-recursive let in the world of (relatively pure) lazy functional programming. The programming language Clean has such non-recursive let and uses it and the shadowing extensively. They consider shadowing a virtue, for uniquely typed data. Richard A. O'Keefe wrote > >> let (x,s) = foo 1 [] in > >> let (y,s) = bar x s in > >> let (z,s) = baz x y s in ... > I really wish you wouldn't do that. > ... > I find that that when the same name gets reused like > that I get very confused indeed about which one I am > looking at right now. > ... > If each instance of the variable is labelled with a > sequence number, I don't get confused because each > variable has a different name and I can *see* which > one this is. > > Yes, sequence numbering variable states is a chore for > the person writing the code, but it's a boon for the > person reading the code. Let me point out the latest Report on the programming language Clean http://clean.cs.ru.nl/download/doc/CleanLangRep.2.2.pdf specifically PDF pages 38-40 (Sec 3.5.4 Let-Before Expression). Let me quote the relevant part: Many of the functions for input and output in the CLEAN I/O library are state transition functions. Such a state is often passed from one function to another in a single threaded way (see Chapter 9) to force a specific order of evaluation. This is certainly the case when the state is of unique type. The threading parameter has to be renamed to distinguish its different versions. The following example shows a typical example: Use of state transition functions. The uniquely typed state file is passed from one function to another involving a number of renamings: file, file1, file2) readchars:: *File -> ([Char], *File) readchars file | not ok = ([],file1) | otherwise = ([char:chars], file2) where (ok,char,file1) = freadc file (chars,file2) = readchars file1 This explicit renaming of threaded parameters not only looks very ugly, these kind of definitions are sometimes also hard to read as well (in which order do things happen? which state is passed in which situation?). We have to admit: an imperative style of programming is much easier to read when things have to happen in a certain order such as is the case when doing I/O. That is why we have introduced let-before expressions. It seems the designers of Clean have the opposite view on the explicit renaming (that is, sequential numbering of unique variables). Let-before expressions have a special scope rule to obtain an imperative programming look. The variables in the left- hand side of these definitions do not appear in the scope of the right-hand side of that definition, but they do appear in the scope of the other definitions that follow (including the root expression, excluding local definitions in where blocks. Notice that a variable defined in a let-before expression cannot be used in a where expression. The reverse is true however: definitions in the where expression can be used in the let before expression. Use of let before expressions, short notation, re-using names taking use of the special scope of the let before) readchars:: *File -> ([Char], *File) readchars file # (ok,char,file) = freadc file | not ok = ([],file) # (chars,file) = readchars file = ([char:chars], file) The code uses the same name 'file' all throughout, shadowing it appropriately. Clean programmers truly do all IO in this style, see the examples in http://clean.cs.ru.nl/download/supported/ObjectIO.1.2/doc/tutorial.pdf [To be sure I do not advocate using Clean notation '#' for non-recursive let in Haskell. Clean is well-known for its somewhat Spartan notation.] State monad is frequently mentioned as an alternative. But monads are a poor alternative to uniqueness typing. Granted, if a function has one unique argument, e.g., World, then it is equivalent to the ST (or IO) monad. However, a function may have several unique arguments. For example, Arrays in Clean are uniquely typed so they can be updated destructively. A function may have several argument arrays. Operations on one array have to be serialized (which is what uniqueness typing accomplishes) but the relative order among operations on distinct arrays may be left unspecified, for the compiler to determine. Monads, typical of imperative programs, overspecify the order. For example, do x <- readSTRef ref1 y <- readSTRef ref2 writeSTRef ref2 (x+y) the write to ref2 must happen after reading ref2, but ref1 could be read either before or after ref2. (Assuming ref2 and ref1 are distinct -- the uniqueness typing will make sure of it.) Alas, in a monad we cannot leave the order of reading ref1 and ref2 unspecified. We must choose the order, even if it is irrelevant. Overspecification inhibits the possible optimizations. Why Clean is relatively unknown? Well, why is Amiga?

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[GSoC] Interactive-diagrams GSoC progress report
by Daniel F 15 Jul '13

15 Jul '13

Hello everyone, I am participating in Haskell.org's Google Summer of Code, working on the interactive-diagrams [1] project. The mid-term evaluations are approaching and I am doing some writeup on the work I did so far: http://parenz.wordpress.com/2013/07/15/interactive-diagrams-gsoc-progress-r… A beta-version of the site is also available to the public: http://paste.hskll.org Please note that this is not a final product and you may experience cryptic error messages, some downtime. The security is pretty tight though :) Any suggestions/comments are welcome. [1] https://google-melange.appspot.com/gsoc/proposal/review/google/gsoc2013/dif… -- Sincerely yours, -- Daniil Frumin

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Homotopy Type Theory IRC Channel
by Darin Morrison 15 Jul '13

15 Jul '13

Hello, I know there are many haskellers interested in dependent type theory so I wanted to mention that there is now an IRC channel on freenode for discussing Homotopy Type Theory (HoTT), e.g., the recent book, possible implementations, dependent type theory in general, etc. The channel is ##hott (NOTE the *two* hashes!) and you can connect directly through freenode's web interface if you don't already have a client: https://webchat.freenode.net/?channels=%23%23hott Currently we have around 50 members but the more the merrier! If you don't know much about IRC but would like to learn more: * http://www.irchelp.org — how IRC works, software clients, FAQs, and other info * http://freenode.net — info about the freenode IRC network specifically Cheers, Darin Morrison

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Re: [Haskell-cafe] What have happened to haskell.org?
by Daniel F 15 Jul '13

15 Jul '13

The web site is migrating. IRC says: Topic for #haskell: haskell.org in the middle of migration; expect turbulence; use www.haskell.org On Mon, Jul 15, 2013 at 6:19 PM, Kirill Zaborsky <qrilka(a)gmail.com> wrote: > On URL http://haskell.org/ I get starting Apache page and 404 on > http://haskell.org/hoogle/ > URL with starting www - http://www.haskell.org/ seems to be working but > http://www.haskell.org/hoogle/ responds with some ELF file. > > Kind regards, > Kirill Zaborsky > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Sincerely yours, -- Daniil -- Sincerely yours, -- Daniil

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What have happened to haskell.org?
by Kirill Zaborsky 15 Jul '13

15 Jul '13

On URL http://haskell.org/ I get starting Apache page and 404 on http://haskell.org/hoogle/ URL with starting www - http://www.haskell.org/ seems to be working but http://www.haskell.org/hoogle/ responds with some ELF file. Kind regards, Kirill Zaborsky

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Compiling haskell-platform-2013.2.0.0 fails
by Roger Mason 15 Jul '13

15 Jul '13

Hello, I'm attempting to compile haskell-platform on an Arch Linux system. It fails very soon after invoking 'make': Configuring HUnit-1.2.5.2... Setup: Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. Use the flag --package-db to specify a package database (it can be used multiple times). If it makes a difference, I'm using GHC 7.6.3 from the Arch package repo. The envar GHC_PACKAGE_PATH mentioned in the error message is unset. Thanks for any help, Roger This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php

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