July 2011 - Haskell-Cafe

ANNOUNCE: docidx-1.0.0
by Andy Gimblett 18 Jul '11

18 Jul '11

Hi all. I'd like to announce docidx, a new tool for Haskell documentation: http://hackage.haskell.org/package/docidx http://github.com/gimbo/docidx.hs docidx is a program which creates a static HTML page indexing your installed packages, with links to your local haddock docs and to each package's hackage page. It covers global and user packages, and handles multiple installed versions sensibly. Here's how the output looks: http://github.com/gimbo/docidx.hs/raw/master/examples/example.png The idea is to complement the "index by module name" which Cabal creates and maintains. Sometimes you want to find things by package. :-) (But note that unlike Cabal's index, docidx's isn't automatically updated when you install a new package; so, I run it once an hour from cron.) Please see the github page for more details, including customisation options. Hopefully somebody will find this useful. Maybe one day it could be part of cabal-install? :-) Thanks! -Andy PS: A bit of history/due credit: Martijn van Steenbergen did something similar in PHP in early 2009: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/53531/focus=53572 ; then I wrote a static version in Python later that year: http://gimbo.org.uk/blog/2009/09/23/ ; then Andy Price ported that to Haskell: https://github.com/andyprice/docidx.hs ; finally, I rewrote that to build the index via Cabal rather than walking the filesystem directly - and here we are. -- Andy Gimblett haskell(a)gimbo.org.uk

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Network.Html simpleTable fonts
by william murphy 17 Jul '11

17 Jul '11

How does one change the font and size of text in a cells in a simpleTable? As in, to change the height, one could state: x = simpleTable [] [height "5"] exampleTable Thanks, Will

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Why aren't files flushed at exit?
by Paul Johnson 17 Jul '11

17 Jul '11

If you open a file for writing and then exit with output unflushed, then Haskell does not flush the file for you. In ghci the program seems to work, but then when you compile it in ghc it mysteriously fails. I've just been bitten by this, but when I went to the bug tracker I found http://hackage.haskell.org/trac/ghc/ticket/4119 ticket 4119, which describes this behaviour and was resolved as "invalid". So presumably this behaviour is by design. Given that most environments get this right, why doesn't Haskell? Paul.

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Contacting Planet Haskell admins
by Michael Snoyman 17 Jul '11

17 Jul '11

Hi, I just sent an email to the Planet Haskell admins, and it bounced back. Apparently it's still forwarding to Don's old email address. Anyone able to update it? Michael

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Re: [Haskell-cafe] Haskell and Databases
by Greg Weber 17 Jul '11

17 Jul '11

Hi Tobias, Have you seen DSH [1]? You might also be interested in Persistent [2], but it sounds like it has different goals than what you are after. [1] http://hackage.haskell.org/package/DSH [2] http://www.yesodweb.com/book/persistent

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Constructor discipline and dependent types.
by Patrick Browne 17 Jul '11

17 Jul '11

Hi, My understanding of the constructor discipline (CD) is that it is a restriction on the form of an equation that guarantees that the equation represents an executable function. The CD restricts the LHS of an equation to consist of a function name, constructors, and variables. Also there should be no new variables on the RHS. So CD permits function to be defined and prohibits general assertions which are more in the domain of a specification language. Question 1: Is the above a reasonable understanding of CD? Question 2: I have read that the lack of dependent types (DT) prevents writing general assertions in Haskell. Is CD related to DT? If so how are they related? Regards, Pat This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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Animas/Yampa: ArrowChoice?
by Ertugrul Soeylemez 16 Jul '11

16 Jul '11

Hello all, I really like the way Animas (fork of Yampa) represents reactive systems, and I would love to write some of my simulations using it. Unfortunately most of what I want to do requires dynamic systems, which can be boiled down to me believing to need an ArrowChoice instance for the SF arrow, because I have to choose between different signal paths depending on the input signal or events. Animas appears to be only suitable for robot-like systems with specific, predefined actors. Is there anything I can do about it? Is it difficult to write the ArrowChoice instance? Or is there a different solution, which I overlooked? Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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urWeb, Haskell and dependent types ....
by Vasili I. Galchin 16 Jul '11

16 Jul '11

Hello, Here is probably a good paper to get people up to speed on dependent types (ironically written by two contributors to this mailing list??): okmij.org/ftp/papers/lightweight-static-capabilities.pdf Vasili

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How to determine minimal dependency of package
by yi huang 15 Jul '11

15 Jul '11

I'm writing my first haskell package, how do i determine the minimal dependency of it, for example, it use Data.Data, how do i know which version of base package first introduce Data.Data module, i can't find the answer with google. -- http://www.yi-programmer.com/blog/

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Domain-Specific Languages: Call for Participation
by Chung-chieh Shan 15 Jul '11

15 Jul '11

DSL 2011: IFIP Working Conference on Domain-Specific Languages 6-8 September 2011, Bordeaux, France **** Call for Participation: Online registration deadline July 30, 2011 **** Details of the program and accommodation are available at http://dsl2011.bordeaux.inria.fr. == Invited Speakers == - Jeremy Gibbons - University of Oxford, UK. - Claude Kirchner - INRIA, France. == Distilled Tutorials on Domain-Specific Languages == The purpose of these tutorials are not to give a general overview, but to make the attendees aware of one point and to make them master it. - Jerzy Karczmarczuk. Specific "scientific" data structures, and their processing. - Oleg Kiselyov. Implementing explicit and finding implicit sharing in embedded DSL. - Keiko Nakata. A total interpreter for While with interactive I/O. - Josef Svenningsson. Combining deep and shallow embeddings for EDSLs. - Walid Taha. Accurate programming: thinking about programs in terms of properties. - William Cook. Build your own partial evaluator in 90 minutes. == DSL Technical Papers == - Basile Starynkevitch. MELT a Translated Domain Specific Language Embedded in the GCC Compiler. - Azer Bestavros and Assaf Kfoury. A Domain-Specific Language for the Incremental and Modular Design of Large-Scale Verifiably-Safe Flow Networks. - Tiark Rompf, Kevin J. Brown, Hassan Chafi, Hyoukjoong Lee, Arvind K. Sujeeth, Martin Odersky and Kunle Olukotun. Building-Blocks for Performance Oriented DSLs. - Dominic Orchard and Alan Mycroft. Efficient and Correct Stencil Computation via Pattern Matching and Static Typing. - Tim Bauer, Martin Erwig, Alan Fern and Jervis Pinto. Adaptation-Based Programming in Haskell. - Eric Walkingshaw and Martin Erwig. A DSEL for Studying and Explaining Causation. - Lucas Beyak and Jacques Carette. SAGA: A DSL for story management.

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