March 2014 - Haskell-Cafe

Main function variables made global.
by Chapman, Anthony Sergio 27 Mar '14

27 Mar '14

?Hello, My problem is as follows (not actual code), I declare a function outside of the main function func w = w * var I get the value of 'var' from a text file in the main function (as the user types the name of the file into terminal) I need a way for 'func' to see what 'var' is without having to change it's type (ie make it into a function which take a 'w' and a 'var'. The reason I can't change the type is that I then pass the function to a PSO module which has strict declarations of a function and I would rather not change the PSO module. I also can't put 'func' into main because 'w' isn't specified. The PSO will find the best w so I don't get it a value. I have thought about making a dummy function which has an input of 'w' and 'var' and an output of a function of just 'w'. Something like: func w = func' w var. I got the function for PSO to optimise and the function to get the data I want from a text file working great, they both do what they're supposed to do. I just need the function of PSO to see the data I get from the file. If you need any more information (sorry if I've been too vague) please let me know. Thank you for your time.?

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2 PhD positions at McMaster
by Jacques Carette 27 Mar '14

27 Mar '14

[The underlying tools in this work will most likely be done in Haskell] PhD Positions Available in the Computing and Software Department at McMaster University For excellent candidates, two PhD positions are available in the Computing and Software Department at McMaster University, in Hamilton, Ontario, Canada. The positions will focus on developing certifiable scientific and engineering software using a Literate Process that eliminates duplication between software artifacts and explicitly incorporates traceability between these artifacts. The motivating case study for the research will be nuclear safety analysis software. Applicants should have a strong background in software engineering or computer science, mathematical maturity and experience with technology and software development. Knowledge of computational mathematics and physics will be considered an asset. Due to the funding model, preference will be given to domestic students or landed immigrants in Canada. Interested candidates should apply for graduate studies with the Computing and Software Department (http://www.cas.mcmaster.ca/cas/0template1.php?1002) and they should send an e-mail expressing interest to one of the project supervisors: Dr. Spencer Smith (smiths(a)mcmaster.ca) Dr. Jacques Carette (carette(a)mcmaster.ca) or Dr. Ned Nedialkov (nedialk(a)mcmaster.ca) Applicants will be accepted until the two positions are filled. The projected start date is September 2014, but this is negotiable. Please feel free to forward this advertisement to any potentially interested candidates. -- Jacques

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Re: [Haskell-cafe] Why does not Haskell have built-in memoization support?
by Andraž Bajt 27 Mar '14

27 Mar '14

Because that would imply you store all calls(parameters and results) during the program execution. And that would require potentialy infinite memory. You might argue that only some need to be memoized. And this is precisely the case. But this reasoning(which to memoize) cannot be fully automated(yet). On Wednesday, March 26, 2014 8:42:32 AM UTC+1, Cosmia Luna wrote: > > Hi everyone, I'm new to Haskell. > > I'm confused about the pure function and lazy evaluation in Haskell. Why > there is not built-in support for memoization, with the fact that calls > with same parameters returns the same result? > > > ---- > Cosmia > >

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ANN: Haskell bindings for Z3: package z3 0.3.2 released
by Iago Abal 27 Mar '14

27 Mar '14

I am happy to announce a new version of the z3 package http://hackage.haskell.org/package/z3 the (unofficial) Haskell bindings for Microsoft's Z3 theorem prover. We didn't announce this package before, but we believe that now it is stable enough to be useful for a broader audience. These bindings are especially appropriate in the following cases: * If your program runs lot of queries, and probably would benefit from incremental solving. Here the performance benefit w.r.t. translating each query to SMT-LIB and calling an external solver should be significant. * If you need to extract interpretations for arrays and functions. * If you need to access specific Z3 features such as Quantifiers or Solvers. We offer three different interfaces: * Z3.Base: a low-level interface, it just performs marshalling. * Z3.Monad: introduces a class MonadZ3 and a concrete monad Z3 that does some bookkeeping for you. Most people seem to be using this interface. * Z3.Lang: a high-level interface in the form of an embedded language. This interface has been deprecated in the current release, we will continue to develop it, but it will be in separate package. The bindings are still incomplete as there are some API functions that have not been added yet. The infrastructure is there, and adding support for new API functions is (most of the times) straightforward. We appreciate that, if you fork the project and add extra functions, then you send the changes back to us. These bindings still use the old Z3 API of Z3 3.x versions, but there is some support for the new API that some people is using satisfactorily. (Z3 4.0 was released while we were still exploring the design of the library and we preferred not to switch to the new API at that time). Full support for the new API should come in the next release. Iago

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Munich Haskell Meeting
by Heinrich Hördegen 26 Mar '14

26 Mar '14

Dear all, our next Haskell meeting in Munich is scheduled for the 31st of March. Exceptionally, we will meet at 19h30 at Theresienstrasse 39 Room A027, 80333 Munich Rene Brunner will present his inaugural speech on Big Data for us. See also the announcment on our site. Afterwards, we will meet at Cafe Puck, as usually. Please help to reserve enough tables by going to http://www.haskell-munich.de/dates and clicking the button. Until then, have a nice time! Heinrich

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ANNOUNCE: wxHaskell 0.90.1.0
by Henk-Jan van Tuyl 26 Mar '14

26 Mar '14

L.S., I am happy to announce a new version of wxHaskell. This version binds to wxWidgets 2.9 [0]. What is it? ----------- wxHaskell is a portable and native GUI library for Haskell. The goal of the project is to provide an industrial strength GUI library for Haskell, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore built on top of wxWidgets – a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel. What's new? ----------- - Added functionality: wxGrid: cell spans, cell renderers (numeric, auto string wrapping), wxScrolledWindow, wxSplitterWindow - Reanimated wxToggleButton, added wxBitmapToggleButton - Solved problem with spaces in pathnames (installation procedure, Windows) - Increased max version of dependencies - The external preprocessor (CPP) is now used - The presence of the wx-config executable is checked at installation time - The bitness of the wxWidgets dynamic libraries is compared to the bitness of the wxHaskell libraries to generate, at installation time; a warning is given when the bitness is incompatible - Documentation improvements - Bugs fixed Links ----- See the homepage of wxHaskell for more information: https://www.haskell.org/haskellwiki/WxHaskell The packages are: - wxc https://hackage.haskell.org/package/wxc - wxdirect https://hackage.haskell.org/package/wxdirect - wxcore https://hackage.haskell.org/package/wxcore - wx https://hackage.haskell.org/package/wx Regards, Henk-Jan van Tuyl [0] https://www.wxwidgets.org/ -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Haskell practice -- Plotting library
by Kai Zhang 26 Mar '14

26 Mar '14

Hi, I've been playing with Haskell for a while. In order to improve my Haskell skills and also due to the lack of an intuitive plotting library, I decided to write a simplified plotting interface for the haskell-chart library. Any comments or suggestions would be very welcome! https://github.com/kaizhang/haskell-plot Kai

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[ANN] haskintex 0.4.0.0 - Haskell code inside a LaTeX document, now with IO!
by Daniel Díaz Casanueva 25 Mar '14

25 Mar '14

Hello haskellers. Good news for the users of haskintex. This release opens new possibilities and solves some frustrations we had in the past. For those who don't know what haskintex is, here is an overview. Haskintex is a program that reads a LaTeX file and evaluates Haskell expressions contained in some specific commands and environments. For example, if you save the file "foo.htex" with: -- foo.htex \documentclass{article} \begin{document} I have \evalhaskell{2+3} fingers in my right hand. \end{document} -- ...and run "haskintex foo", you will get the following output: \documentclass{article} \begin{document} I have \verb`5` fingers in my right hand. \end{document} Just as you expected. If you want to know more details, visit the haskintex site at: http://daniel-diaz.github.io/projects/haskintex What is new in this release? We have added two new features: * \iohatex{t}, where t :: IO LaTeX. It works exactly as the \hatex command does, but it expects an input of type IO LaTeX. This means you can perform IO computations now! * \begin{haskellpragmas}...\end{haskellpragmas} This will allow to include pragmas in the temporal Haskell module. In addition to these two features, a new flag can be passed to the program: -debug. It writes down in a file the representation of the input that haskintex uses internally. It can be useful in those cases that you are not getting the output you expect. And that's it for now. The code didn't grow much (and I want it to stay small) but I think possibilities have grown substantially. If you want to give it try, run "cabal update" followed by "cabal install haskintex". Good luck, Daniel Díaz.

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Cabal robustness
by Dominick Samperi 24 Mar '14

24 Mar '14

I have seen the dreaded "ExitFailure 1" many times when a package fails to install (under Linux or Windows), and I wonder why something more helpful cannot be printed? Sometimes one gets a variant of this where the message is "this system is not compatible with this package," but the user must study the foo.cabal file to determine what is missing. Also, it seems that the only way to determine if a package will install under Windows is to try and hope for the best (often getting "ExitFailure 1" if it fails). Wouldn't it make more sense to tag packages with the OS and other dependencies and fail with a helpful message like "Windows not supported" if appropriate? It appears that some packages (like lens-4.1) have version dependencies that cannot be satisfied (at least not on my Linux and Windows boxes), so it appears that the Hackage hosting process suffers from a variant of the well-known "dll hell" problem. I tried the new (Cabal 1.18.0) sandbox feature but this did not help in my case. Any comments on these issues would be appreciated. Thanks, Dominick

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HaL-9 - Call for Contributions
by Henning Thielemann 24 Mar '14

24 Mar '14

HaL ist ein lokaler Haskell-Workshop mit überregionaler Bedeutung, der nun bereits das 9. Mal stattfindet. Dieses Jahr laden wir für den 20. Juni ins Institut für Informatik an der Martin-Luther-Universität Halle-Wittenberg ein. Wir suchen Beiträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, aber auch Anknüpfungen an andere Programmierparadigmen. Dabei interessieren wir uns unter anderem für die Themenbereiche * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre und Forschung an Schulen und Hochschulen. Die Beiträge können präsentiert werden als * Tutorium (etwa 90 min) * Vortrag (etwa 30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, nach Absprache auch Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (max. 3 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen, sowie eine knappe Zusammenfassung von etwa 100 Wörtern. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell oder funktionaler Programmierung), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Senden Sie die Beitragsvorschläge als PDF-Dokument bis zum 27. April 2014 an hal-committee(a)iba-cg.de Wir werden Ihnen bis zum 9. Mai mitteilen, ob wir Ihren Beitrag in das Programm aufnehmen. Für das Organisationsteam Henning Thielemann

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