August 2014 - Haskell-Cafe

tree insert and laziness
by Semen Trygubenko / Семен Тригубен ко 18 Aug '14

18 Aug '14

Dear Haskell-Cafe, I'm presently reviewing a translation of the following paragraph (taken from LUaH, chapter 8): http://learnyouahaskell.com/making-our-own-types-and-typeclasses "In languages like C, we'd do this by modifying the pointers and values inside the tree. In Haskell, we can't really modify our tree, so we have to make a new sub-tree each time we decide to go left or right and in the end the insertion function returns a completely new tree, because Haskell doesn't really have a concept of pointer, just values. Hence, the type for our insertion function is going to be something like a -> Tree a - > Tree a. It takes an element and a tree and returns a new tree that has that element inside. This might seem like it's inefficient but laziness takes care of that problem." If it is really the laziness that makes this approach efficient? If it isn't, what did the author want to say in the last sentence? Thank you, Semen -- Семен Тригубенко http://trygub.com

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Haskell SDL2 FRP games working on Android
by Ivan Perez 18 Aug '14

18 Aug '14

Hi Café Answering recent questions posted on this list regarding FRP, I would like to announce that we have a working Android game written in Haskell, using SDL2 and Yampa. A short article describing the implications that this could have, together the libraries and backend we used, is here: http://keera.co.uk/blog/2014/08/13/most-inspiring-green-screen-you-will-eve… Changes made to existing libraries will be published as we move towards releasing the game on Google Play, and so will examples of Android programs written in Haskell. All the best Ivan -- Facebook: https://www.facebook.com/keerastudios Twitter: https://twitter.com/KeeraStudios Web: http://www.keera.co.uk

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Fully funded PhD position on Computational Logic/Functional Programming/Interactive Theorem Proving, University of Dundee, Scotland
by Ekaterina Komendantskaya 18 Aug '14

18 Aug '14

One fully funded PhD position on Computational Logic/Functional Programming/Interactive Theorem Proving is available at the University of Dundee, Scotland. For more information, please email katya(a)computing.dundee.ac.uk or refer to: https://docs.google.com/document/d/10Cnlws_XPKrimo9m_CKPSXUZFCkP8FhBfD9a9xA… The funding is provided by EPSRC Doctoral Training Partnership Scheme, and is available for UK residents only. Katya Ekaterina Komendantskaya Senior Lecturer, Head of PhD Studies Room 1.04, Queen Mother Building School of Computing, University of Dundee Scotland, DD14HN Tel: (+44) 01382384820

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Wish list for GHC API tooling support
by Alan & Kim Zimmerman 18 Aug '14

18 Aug '14

At the moment the GHC API is a sort of poor relation in the haskell world, where it could be a significantly useful resource for the growing list of haskell tool providers. Based on my experiences with HaRe, I have started putting together a wish list of features I would like to see in it, which is here https://github.com/fpco/haskell-ide/wiki/GHC-API I welcome feedback / discussion on this. Regards Alan

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Haskell developer roles at Standard Chartered
by Don Stewart 17 Aug '14

17 Aug '14

Hi Cafe, The Strats team at Standard Chartered is hiring expert typed FP developers for Haskell dev roles in London. This is a "front office" finance role - meaning you will work directly with traders building software to automate and improve their efficiency. The role is very development focused, and you will use Haskell for almost all tasks: data analysis, DSLs, market data publishing, databases, web services, desktop GUIs, large parallel tasks, quantitative models, solvers, everything. There may be a small amount of C++ or F# on occasion. This is a fast paced role - code you write today will be deployed within hours to hundreds of users and has to work. You will join an expert team in London, and significant, demonstrable experience in typed FP (Haskell, OCaml, F# etc) is strongly preferred. We have more than 2 million lines of Haskell, and our own compiler. In this context we look for skill and taste in typed API design to capture and abstract over complex, messy systems. Experience writing typed APIs to external systems such as databases, web services, pub/sub platforms is very desirable. We like working code, so if you have Hackage or github libraries, we want to see them. We also like StackOverflow answers, blog posts, academic papers, or other arenas where you can show broad FP ability. The role requires physical presence on the trading floor in London. Remote work isn't an option. Ideally you have some project and client management skills -- you will talk to users, understand their problems, and then implement and deliver what they really need. No financial background is required. If this sounds exciting to you, please send CVs to dons00 at gmail.com

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Issues with Marshalling arrays of user defined types
by lonetiger＠gmail.com 17 Aug '14

17 Aug '14

Hi All, I’ve been scratching my head for weeks trying to figure out what goes wrong with the code pasted below. It’s compiled to a shared library (dll) on windows. I know the Storable instance is correct because calls to testFooA works, but calls to testFooListA get an invalid pointer back. Lists of Ints do work fine, so it seems that newArray is also working. In GHCi it can dereference the pointer. And this used to work before in earlier GHC 7.0 and later 6.6 builds. Using WinDBG and gflags I see that the pointer is indeed invalid, but that the *valid* data is there in the heap. The example code can be found at http://lpaste.net/6148884045213204480 Anyone have an idea what I’m doing wrong? Kind Regards, Tamar

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GHC panic!
by 北原真一 17 Aug '14

17 Aug '14

I am asking for help I am Haskeller of Japan I'm using GHC7.6.3 GHC has caused the panic https://gist.github.com/minamiyama1994/6697c3fb9c345da6715f

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HsUnix.h on Ubuntu Linux
by Vasili I. Galchin 16 Aug '14

16 Aug '14

1) I forgot how to get this include file 2) where does it go under /usr/include ???

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The Good, the Bad and the GUI
by Wojtek Narczyński 16 Aug '14

16 Aug '14

Dear All, Haskell is great for great many areas, let me name just two: - parsers, translators, interpreters, compilers; highly concurrent systems. Haskell is however not great for GUIs. I've been thinking a little why this is so. I think one of the reasons might be that in Haskell it is unusual to deal with data that is incomplete or otherwise erroneous. Let me try to explain, what I mean, by example. If you declare Person class in Java, you automatically get a thingy that you can readily use in UI construction, because all the fields can temporarily be null, even the required ones. In Haskell you'd need two data types: the usual proper Haskell data type, and another which wraps every field in Maybe, facilitates editing, validation, etc. Perhaps it would be possible to generate one data type from the other, or generate both from a common specification. Let me write the same thing in other words. It is not controversial to say on this list that specifying what is correct means, is a good idea. But for GUIs, in addition to the strong type, you need another relaxed type to hold the values temporarily, until the human manages to deliver correct data, often by trial and error. Comments welcome. -- Kind regards, Wojtek Narczyński

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Re: [Haskell-cafe] HaskellWiki page about SDL
by Henk-Jan van Tuyl 15 Aug '14

15 Aug '14

FYI On Fri, 15 Aug 2014 01:26:09 +0200, Irene Knapp <irene.knapp(a)icloud.com> wrote: > For some reason, although I’m subscribed to the mailing list, I’m not > allowed to send stuff to it (not that I’ve ever wanted to before). > Sorry for the private reply! Feel free to forward it to the list if you > wish. > > I haven’t tried in a while, but the problem is that on OS X, the SDL > library defines its own main() which invokes the user-provided main(), > and the C header file does #define main _SDL_main to make this “work” as > long as an FFI isn’t involved. > > I checked the SDL Mercurial repo, and it still does this: > > http://hg.libsdl.org/SDL/file/74356aed1fa2/include/SDL_main.h > <http://hg.libsdl.org/SDL/file/74356aed1fa2/include/SDL_main.h> > > So yes, the problem still exists. There is no easy workaround, either; > for Haskell code to run as a library rather than an executable requires > a special wrapper in C to initialize the runtime. > > Irene > >> On Aug 14, 2014, at 3:43 PM, Henk-Jan van Tuyl <hjgtuyl(a)chello.nl> >> wrote: >> >> >> L.S., >> >> Does the problem with SDL on OS X, as mentioned on the HaskellWiki page >> about SDL[0], still exist? This text is quite old and I would like to >> remove it. >> >> Regards, >> Henk-Jan van Tuyl >> >> >> [0] https://www.haskell.org/haskellwiki/SDL#Haskell-SDL_with_Mac_OS_X Regards, Henk-Jan van Tuyl -- 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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