August 2009 - Haskell-Cafe

Re: [Haskell-cafe] Chicago Haskell User Group?
by Louis Wasserman 12 Aug '09

12 Aug '09

Count me in. I'm a student at UChicago. Louis Wasserman wasserman.louis(a)gmail.com

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Database written in Haskell?
by Günther Schmidt 12 Aug '09

12 Aug '09

Hi, is there an SQL database written in Haskell like HSQLDB which is written in Java? Günther

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Examples
by Andrew Coppin 12 Aug '09

12 Aug '09

As some of you may remember, I recently released a couple of packages on Hackage. I'd like to also release some example programs using these packages, but I'm not sure of the best way to do this. Do I make the example programs part of the package itself? Do I release a seperate package which just contains the example code? Something else entirely? What's the recommendation here?

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Next BostonHaskell meeting: August 18th at MIT
by Ravi Nanavati 12 Aug '09

12 Aug '09

I'm pleased to announce the August meeting of the Boston Area Haskell Users' Group. Based on the feedback from the July meeting and the constraints of our speakers, the August meeting has been scheduled for Tuesday, August 18th from 6:30pm - 8:30pm. Like the past two meetings, it will be held in the MIT CSAIL Reading Room (32-G882, i.e. a room on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). We're making a slight departure from our meeting format this month. Our featured speaker will be Edward Kmett, who will be sharing a two-part presentation focusing on monoids and parsing. The first part of Edward's presentation is titled "Introduction to Monoids". After the first part of Edward's presentation, Shae Erisson will be presenting short overview of Haskell and emacs integration. Following Shae, Paul Chiusano will be talking briefly about functional programming opportunities at ClariFI (the job advertisement he recently posted to the BostonHaskell list). Paul is planning to be available to talk to anyone interested during our customary break. As you might guess, there isn't really room for Lightning Talks or other advertisements in August, but please feel free to contact me if you have something you'd like to talk about at a future meeting (since we're still very hungry for content for future meetings). After the break, Edward will be picking up with the second part of his presentation: "A Parallel Parsing Trifecta: Iteratees, Parsec, and Monoids". We're trying a new attendance poll this month: http://doodle.com/participation.html?pollId=x8rbbbprtezdtaan As before, responding to this poll will help with two things: 1. Getting an idea of what fraction of the Boston-area Haskell community can and can't attend this meeting (to help with future scheduling). 2. Giving me an estimated count of attendees, since I have talked my wife into baking some more goodies and bringing drinks again. Sponsorship of or other assistance with refreshments is still being eagerly solicited. I'm also still having trouble embedding this poll in a page on our Google Group, so if anyone has any ideas about that, please feel free to try (any group member can edit pages) and/or offer other assistance or suggestions. If you have any questions about the meeting please send them to the BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the August meeting! Thank you, - Ravi Nanavati

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Finalizers on FunPtrs
by Maurício CA 12 Aug '09

12 Aug '09

I see in Foreign.Ptr documentation that it is good practice to call freeHaskellFunPtr when a pointer to a Haskell function (obtained using 'dynamic' stubs) is not going to be used anymore. Is it possible to do that in a way that is similar to ForeignPtr behavior, where pointers are finalized when GC knows they're not going to be used anymore? See this attempt: In an IO monad: a <- giveMeFunPtr b <- castFunPtrToPtr a :: IO (Ptr something) foreignFunPtr <- newForeignPtr funPtrFinalizer b :: IO (ForeignPtr something) With funPtrFinalizer a FunPtr to: baseFunPtrFinalizer p = freeHaskellFunPtr . castPtrToFunPtr p Is something like that expected to work, i.e., would I get a ForeignPtr that I could cast and give to foreign functions, and still expect that my function pointer would be freed when not needed anymore? Thanks, Maurício

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Re: [Haskell-cafe] Haskell's type system compared to CLOS
by Matthias-Christian Ott 11 Aug '09

11 Aug '09

On Tue, Aug 11, 2009 at 11:20:02PM +0100, Philippa Cowderoy wrote: > Matthias-Christian Ott wrote: >> What has Haskell to provide what Common Lisp and Dylan haven't? > Static typing (with inference). Very large difference, that. That's true. This is a big advantage when compiling programmes. But as far as I know type inference is not always decidable in Haskell. Am I right? Dylan does type inference too and Hannes Mehnert is currently working on better type inference for the dylan compiler [1]. Regards, Matthias-Christian [1] https://berlin.ccc.de/wiki/Dem_Compiler_beim_Optimieren_zuschauen

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ANNOUNCE: HacPDX, A Hackathon in Portland
by Thomas DuBuisson 11 Aug '09

11 Aug '09

HacPDX is an opportunity for Portland Haskell hackers to join together in building and improving libraries and tools. If you've never been, hackathons are typically not only a good opportunity for experienced devs to work together but also a great way for newcomers to get involved in the community. WHEN Friday Sept 25 3:30PM to 6:00 PM Saturday Sept 26 10:00AM to 6:00 PM Sunday Sept 27 10:00AM to 6:00 PM We can work however late, but tentatively let's plan on eating and sleeping. The Friday times give an opportunity to meet and test your network connectivity, should you so desire. Afterwards we can head out to grab a pint! WHERE We will be in rooom 86-01 (downstairs) of the fourth avenue building (1900 SW 4th Ave), which is part of Portland State University. As the building is locked during the weekends, I'll be letting attendees in via the Harrison Street entrance. EQUIPMENT You should bring a laptop with wireless (802.11). The room has whiteboards and a projector for any discussions or should anyone wish to give a talk. Further Information is available on the wiki [1]. Suggestions, wiki edits, organization and coordination help are all welcome. Thomas DuBuisson [1] http://haskell.org/haskellwiki/HacPDX

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Haskell's type system compared to CLOS
by Matthias-Christian Ott 11 Aug '09

11 Aug '09

Hi, usually I'm sceptical of programming languages which are not based on the von Neumann architecture, but recently I got interested in functional programming languages. The arrogance of lots of Haskell users, who made me feel that using a programming language other than Haskell is a waste of time, combined with vanguard mathematical notation has been very attractive to me and I have decided to get at least an idea of Haskell and its concepts. Some weeks ago I learned programming in Dylan and was impressed by its object system which is basically a stripped version of CLOS. Multiple dispatch together with a well-thought-out object system is quite powerful, because it removes the burden of including methods in the class definition. At the moment I'm reading the "Functional Programming using Standard ML" and I'm in the chapter on data types. This afternoon it occurred to me that classes and data types are symmetric. In a class hierarchy you start an abstract super class (the most abstract is the class object in some languages) and further specialise them via inheritance; with data types you can start with specialized versions and abstract them via constructors (I'm not sure how message sending to a superclass looks like in this analogy). Anyhow, I also came across an interesting presentation. Andreas Löh and Ralf Hinze state in their presentation "Open data types and open functions" [1]: * OO languages support extension of data, but not of functionality. * FP languages support extension of functionality, but not of data. Their first point refers to the fact that in most object-oriented languages don't allow the separate definition of classes and their respective methods. So to add new functions, you have edit the class definitions. However, in functional programming languages you can easily add new functionality via pattern matching, but have to either introduce new types or new constructors, which again means to modify existing code. In Dylan (and in Common Lisp) you define methods separate from classes and have pattern matching based on types. This solves all mentioned problems. So my question is, how are algebraic data types in Haskell superior to CLOS (despite the fact that CLOS is impure)? How do both compare? What has Haskell to provide what Common Lisp and Dylan haven't? Thanks! Regards, Matthias-Christian [1] http://people.cs.uu.nl/andres/open-japan.pdf

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Galois is Hiring
by Don Stewart 11 Aug '09

11 Aug '09

Galois is continuing to hire. We will also be at ICFP and related events, so come and see Lee Pike or me. We have multiple positions for talented functional programmers (with both junior and senior positions). A strong functional programming ability is an advantage (you will be programming in Haskell), and a good computer science background is required. Experience with compilers, operating systems, networking, security, and formal methods is of particular interest. Galois is based in Portland, Oregon. Our engineers work with functional languages, designing and developing advanced technologies for safety and security-critical systems, networks, and applications. Galois technical staff members play a pivotal role in developing advanced software technology. Enginners work in small team settings, and must successfully interact with clients, partners, and other employees in a highly cooperative, collaborative, and intellectually challenging environment. Technical staff may be called upon to write proposals, gather requirements, and work in all stages of the software development process, from requirements gathering to testing and validation. Additional duties may include project management, technology research and development, and technical infrastructure development. We’re looking for people who can invent, learn, think, and inspire. We reward creativity and thrive on collaboration. We offer great benefits and perks, including a 401K plan, stock options, paid vacation, family health plan, flexible work schedule, a casual work environment, snacks, espresso and foosball. A Masters or Ph.D. degree in Computer Science is desirable. Additionally, a strong programming background and experience with Haskell or other functional programming languages is preferred. You must work well with customers, including building rapport, identifying needs, and communicating with strong written, verbal and presentation skills. Must be highly motivated and able to self-manage to deadlines and quality goals. To learn more about us, visit http://www.galois.com and http://www.galois.com/company/careers The types of technology we use are covered in our blog: http://www.galois.com/blog/ We’d like to hear from you! Send your cover letter and resume to us at jobs2009 at galois.com.

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GTK2HS OpenGL demo doesn't work on Vista when compiled?
by Peter Verswyvelen 11 Aug '09

11 Aug '09

GTK2HS 0.10.1 comes with an OpenGL demo (share/demo/opengl/RotatingCube.hs) On my machine (Vista 32-bit) it runs fine under GHCi, but not when compiling using GHC (no rendering happens, unless I resize the window, then rendering happens from time to time) I'm using GHC 6.10.3 (installed Haskell Platform 2009.2.0.1). Do other people using Windows experience this problem? Cheers, Peter Verswyvelen

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