April 2015 - Haskell-Cafe

Maintenance of feed package
by Adam Bergmark 20 Apr '15

20 Apr '15

Hi café, Sigbjorn. I emailed Sigbjorn a week ago asking whether he was still maintaining the `feed' package. I haven't received a reply, and I haven't been able to find any sign of him online recently. Unless he resurfaces I'd like to take over as maintainer of the package to publish the changes required for GHC 7.10 compatibility and other dependencies that have fallen out of date. See: https://github.com/sof https://github.com/sof/feed/pulls https://github.com/haskell-infra/hackage-trustees/issues/12 Regards, Adam

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ANN: hsreadability-1.0.0
by Alexey Shmalko 19 Apr '15

19 Apr '15

I'm pleased to announce the first release of hsreadability: Haskell bindings to the Readability API [1]. The Readability provides three services for developers: Reader, Parser and Shortener: - Reader provides access to the user's info, bookmarks, articles and tags; - Parser is an interface to the powerful web content parser; - Shortener is a URL shortener (doesn't require authentication). With hsreadability you're able to access all the functionality of these services from Haskell. If you have any issues, report them on the GitHub page [2]. I'd also love to hear any other feedback so feel free to comment here or email me. Best regards, Alexey Shmalko [1] https://readability.com/developers/api [2] https://github.com/rasendubi/hsreadability

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Scala at position 25 of the Tiobe index, Haskell dropped below 50
by Henk-Jan van Tuyl 19 Apr '15

19 Apr '15

L.S., From the Tiobe index page[0] of this month: Another interesting move this month concerns Scala. The functional programming language jumps to position 25 after having been between position 30 and 50 for many years. Scala seems to be ready to enter the top 20 for the first time in history. Haskell dropped from the top 50 last month and hasn't come back. I suppose, if Haskell compiled to JVM, Haskell would have a much wider audience. Regards, Henk-Jan van Tuyl [0] http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html -- 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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dependency issues on a new install of haskell-platform 2014.2.0.0 64bit on OSX
by Anatoly Yakovenko 18 Apr '15

18 Apr '15

so I keep seeing failures in some modules, but if i install them by hand things get resolved. How do i get cabal to do this for me? so the dependencies: criterion -> monad-par-0.3.4.7 -> parallel-3.2.0.4 which fails but installing parallel-3.2.0.6 unravels the broken dependency chain. Below is the output: cabal: Error: some packages failed to install: criterion-1.1.0.0 depends on monad-par-0.3.4.7 which failed to install. monad-par-0.3.4.7 failed during the building phase. The exception was: ExitFailure 1 statistics-0.13.2.3 depends on monad-par-0.3.4.7 which failed to install. anatolys-MacBook:rbm anatolyy$ cabal install monad-par Resolving dependencies... Configuring monad-par-0.3.4.7... Building monad-par-0.3.4.7... Failed to install monad-par-0.3.4.7 Last 10 lines of the build log ( /Users/anatolyy/.cabal/logs/monad-par-0.3.4.7.log ): Building monad-par-0.3.4.7... Preprocessing library monad-par-0.3.4.7... <command line>: cannot satisfy -package-id parallel-3.2.0.4-c330f8c64fe6816637464ee78fcb9a93 (use -v for more information) cabal: Error: some packages failed to install: monad-par-0.3.4.7 failed during the building phase. The exception was: ExitFailure 1 anatolys-MacBook:rbm anatolyy$ cabal install parallel Resolving dependencies... Downloading parallel-3.2.0.6... Configuring parallel-3.2.0.6... Building parallel-3.2.0.6... Installed parallel-3.2.0.6 Updating documentation index /Users/anatolyy/Library/Haskell/share/doc/index.html anatolys-MacBook:rbm anatolyy$ cabal install monad-par Resolving dependencies... Configuring monad-par-0.3.4.7... Building monad-par-0.3.4.7... Installed monad-par-0.3.4.7 Updating documentation index /Users/anatolyy/Library/Haskell/share/doc/index.html

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Re: [Haskell-cafe] Graph diagram tools?
by Ivan Lazar Miljenovic 17 Apr '15

17 Apr '15

Wow, you really have resurrected an old thread! On 17 April 2015 at 03:12, Ivan Zakharyaschev <imz(a)altlinux.org> wrote: > Hi, > > I have some feedback on the API of the graphviz library's monadic API > (resulting form my explorations written down at > http://mathoverflow.net/a/203099/13991 ). > > Le jeudi 23 juin 2011 04:38:21 UTC+4, Ivan Lazar Miljenovic a écrit : >> >> On 23 June 2011 02:48, Stephen Tetley <stephen...(a)gmail.com> wrote: >> > Or Andy Gill's Dotgen - simple and stable: >> > >> > http://hackage.haskell.org/package/dotgen >> >> Within the next month, I should hopefully finally finish the new >> version of graphviz. Various improvements include: >> >> As such, I would greatly appreciate knowing what it is that makes you >> >> want to use a different library (admittedly the graphviz API isn't as >> stable as the others, but that's because I keep trying to improve it, >> and typically state in the Changelog exactly what has changed). >> >> > > ### graphviz Haskell library and other ones > > An alternative to "graphviz" Haskell package mentioned in > [haskell-cafe](https://groups.google.com/d/msg/haskell-cafe/ZfZaw2E9a18/xZ0O… > is [dotgen](http://hackage.haskell.org/package/dotgen). > > In [a > follow-up](https://groups.google.com/d/msg/haskell-cafe/ZfZaw2E9a18/9P-dazc… > to the post mentioning `dotgen`, the author of graphviz gives some > comparison between them (and other similar Haskell libs). I assume his > "plans" (about a monadic interface) have been implemented already: Yup: http://hackage.haskell.org/package/graphviz-2999.17.0.2/docs/Data-GraphViz-… > >> Within the next month, I should hopefully finally finish the new >> version of graphviz. Various improvements include: >> >> ... >> >> * A Dot graph representation based loosely upon **dotgen**'s monadic >> interface (with Andy's blessing) but with the various Attributes being >> used rather than (String, String). I think I'm going to be able to >> make it such that you can define a graph using the monadic interface >> that will almost look identical to actual Dot code. >> >> ... >> >> I would like to stress to people considering using other bindings to >> Graphviz/Dot (such as **dotgen**, language-dot, or their own >> cobbled-together interface): be very careful about quoting, etc. I >> have spent a _lot_ of time checking how to properly escape different >> values and ensuring correctness under the hood (i.e. there is no need >> to pre-escape your Text/String values; graphviz will do that for you >> when generating the actual Dot code). This, after all, is the point >> of having existing libraries rather than rolling your own each time. > > Both points are related. (So, graphviz's monadic iterface is a safer > improvement upon dotgen's one.) > > ### Considering dotgen vs graphviz closer > > But looking into the examples, I see that `dotgen` can use "Haskell > ids" to identify created nodes, whereas in graphviz's monad (see the > example above) one must supply extra strings as the unique ids (by > which we refer to the nodes). I used Strings as an example, as I was directly converting an existing piece of Dot code; the original can be found here: http://hackage.haskell.org/package/graphviz-2999.17.0.2/docs/Data-GraphViz-… But, you can use any type you like for the node identifiers, as long as you make them an instance of the PrintDot class. That's where the `n` in the `Dot n` type comes in. > > I like the first approach more ("Haskell ids"). I admittedly don't have any ability in graphviz to create new identifiers for you. I could (just add a StateT to the internal monadic stack which keeps track of the next unused node identifier) but I think that would _reduce_ the flexibility of being able to use your own type (it would either only work for `Dot Int`, or even if you could apply a mapping function to use something like `GraphID`, but that has a problem if you have a `Double` with the same value - and hence same textual representation - as your Int). The way I see it, graphviz is usually used for converting existing Haskell values into Dot code and then processing with dot, neato, etc. the Monadic interface exists so that you can still use the library for static pre-specified graphs (I wrote the module for a specific use case, but in practice found it not as useful as I thought it would be as I typically don't have a need for static graphs in my Haskell code). > > Cf. dotgen (from > <https://github.com/ku-fpg/dotgen/blob/master/test/DotTest.hs>): > > module Main (main) where > import Text.Dot > -- data Animation = Start > src, box, diamond :: String -> Dot NodeId > src label = node $ [ ("shape","none"),("label",label) ] > box label = node $ [ ("shape","box"),("style","rounded"),("label",label) > ] > diamond label = node $ > [("shape","diamond"),("label",label),("fontsize","10")] > main :: IO () > main = putStrLn $ showDot $ do > attribute ("size","40,15") > attribute ("rankdir","LR") > refSpec <- src "S" > tarSpec <- src "T" > same [refSpec,tarSpec] > c1 <- box "S" > c2 <- box "C" > c3 <- box "F" > same [c1,c2,c3] > refSpec .->. c1 > tarSpec .->. c2 > tarSpec .->. c3 > m1 <- box "x" > m2 <- box "y" > ntm <- box "z" > same [m1,m2,ntm] > c1 .->. m1 > c2 .->. m2 > xilinxSynthesis <- box "x" > c3 .->. xilinxSynthesis > gns <- box "G" > xilinxSynthesis .->. gns > gns .->. ntm > ecs <- sequence > [ diamond "E" > , diamond "E" > , diamond "Eq" > ] > same ecs > m1 .->. (ecs !! 0) > m1 .->. (ecs !! 1) > m2 .->. (ecs !! 0) > m2 .->. (ecs !! 2) > ntm .->. (ecs !! 1) > ntm .->. (ecs !! 2) > _ <- sequence [ do evidence <- src "EE" > n .->. evidence > | n <- ecs > ] > edge refSpec tarSpec > [("label","Engineering\nEffort"),("style","dotted")] > () <- scope $ do v1 <- box "Hello" > v2 <- box "World" > v1 .->. v2 > (x,()) <- cluster $ > do v1 <- box "Hello" > v2 <- box "World" > v1 .->. v2 > -- x .->. m2 > -- for hpc > () <- same [x,x] > v <- box "XYZ" > v .->. v > () <- attribute ("rankdir","LR") > let n1 = userNodeId 1 > let n2 = userNodeId (-1) > () <- n1 `userNode` [ ("shape","box")] > n1 .->. n2 > _ <- box "XYZ" > _ <- box "(\n\\n)\"(/\\)" > netlistGraph (\ a -> [("label","X" ++ show a)]) > (\ a -> [succ a `mod` 10,pred a `mod` 10]) > [ (n,n) | n <- [0..9] :: [Int] ] > return () > My preference - and hence overall design with graphviz - is that you would generate the graph first, and _then_ convert it to a Dot representation en masse. > > Cf. graphviz with string ids: > > A short example of the monadic notation from [the > documentation](http://hackage.haskell.org/package/graphviz-2999.16.0.0/docs…: That version is a tad out of date, but shouldn't affect this. > > digraph (Str "G") $ do > > cluster (Int 0) $ do > graphAttrs [style filled, color LightGray] > nodeAttrs [style filled, color White] > "a0" --> "a1" > "a1" --> "a2" > "a2" --> "a3" > graphAttrs [textLabel "process #1"] > > cluster (Int 1) $ do > nodeAttrs [style filled] > "b0" --> "b1" > "b1" --> "b2" > "b2" --> "b3" > graphAttrs [textLabel "process #2", color Blue] > > "start" --> "a0" > "start" --> "b0" > "a1" --> "b3" > "b2" --> "a3" > "a3" --> "end" > "b3" --> "end" > > node "start" [shape MDiamond] > node "end" [shape MSquare] > > Thanks for the packages, and best wishes, > Ivan Z. -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Re: [Haskell-cafe] Scala at position 25 of the Tiobe index, Haskell dropped
by Gregory Guthrie 17 Apr '15

17 Apr '15

I find that Haskell has a very different learning curve from other languages that I use/know/have-tried, in that the basic language itself is very simple and easy to learn and appreciate. However once one starts using a lot of monads and applicatives and other libraries, it can begin to look more like APL. >>> parser >>= >>> ( \s -> return ( pl' { P.payloadData = setField pld (Just s) } } ) ) Certainly one can learn to parse and read this, but with all of the new operators and thus syntax not familiar to standard IP language users. (Not a complaint, just an observation from teaching this to students new to FP.) And in my experience the cabal problems are the "fatal-flaw"; it is not infrequent that I have had to delete all libraries and start over, and I have only very simple usage. I would not want to have a business project that depended on this, as often I have not found a good solution where I could install all the packages I wanted. (Perhaps I just need to learn more about sandboxing techniques.) I am not a fan of the Scala syntax, but it does seem to be an easier transition because it look-and-feel's more like the typical IPs. ------------------------------------------- > -----Original Message----- ...

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Re: [Haskell-cafe] [Haskell-beginners] texture mapping with SDL
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 17 Apr '15

17 Apr '15

On 17 April 2015 at 19:28, Florian Gillard <florian.gillard(a)gmail.com> wrote: > Hi everyone, > > I am not sure my previous message went trough, if so, sorry for the double > post. > > I am trying to make a basic raycaster (something like the first > wolfenstein 3D) using haskell and SDL 1.2 > > So far I have it working using coloured lines and I would like to know if > there is any way to apply transforms to textures loaded in memory using > SDL, in order to achieve basic texture mapping on the walls. > > I looked at the SDL doc but I didn't find anything looking like what I > need. > > The code is there: > > https://github.com/eniac314/maze-generator/blob/master/raycaster.hs > > sreenshot here: > https://github.com/eniac314/maze-generator/blob/master/raycaster.png > > (the last part is not done yet but has nothing to do with the raycaster) > > I would appreciate any suggestion :) > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > > The message got through. It might be better answered on the haskell-cafe so I'm relaying it there. -- Regards Sumit Sahrawat

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Coding katas/dojos and functional programming introduction
by Gautier DI FOLCO 17 Apr '15

17 Apr '15

Hello, Some days ago I have participated to a coding dojo* which aimed to be an introduction to functional programming. I have also facilitate 3 of events like this and do several talks on this subject. But I'm kinda disappointed because each time there is a common pattern: 1. Unveil the problem which will be treated 2. Let the attendees solve it 3. Show the FP-ish solution (generally a bunch of map/fold) I think it's frustrating for the attendees (because they don't try to solve it) and gives a false illusion of knowledge. I don't consider myself as a "FP guru" or anything but for me FP is a matter of types and expressions, so when someone illustrate FP via map/fold, it's kind of irritating. Ironically, the best workshop I have done was on functional generalization (you begin by two hard coded functions, sum and product, and you extract Foldable and Monoid), but again, it's not satisfying. We can do better, we should do better. Have you got any feedback/subjet ideas/examples on how to introduce "real" FP to beginners in a short amount of time (like 1-3 hours)? Thanks in advance for your help. Regards. * Basically you have 2 to 3 hours, a problem and you try to solve with in iteration with different constraints

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Ongoing IHG work to improve Hackage security
by Duncan Coutts 17 Apr '15

17 Apr '15

All, The IHG members identified Hackage security as an important issue some time ago and myself and my colleague Austin have been working on a design and implementation. The details are in this blog post: http://www.well-typed.com/blog/2015/04/improving-hackage-security We should have made more noise earlier about the fact that we're working on this. We saw that it was important to finally write this up now because other similar ideas are under active discussion and we don't want to cause too much unnecessary duplication. The summary is this: We're implementing a system to significantly improve Hackage security. It's based on a sensible design (The Update Framework) by proper crypto experts. The basic system is fully automatic and covers all packages on Hackage. A proposed extension would give further security improvements for individual packages at the cost of a modest effort from package authors. http://theupdateframework.com/ It will also allow the secure use of untrusted public Hackage mirrors, which is the simplest route to better Hackage reliability. As a bonus we're including incremental index downloads to reduce `cabal update` wait times. And it's all fully backwards compatible. I should also note that our IHG funding covers the first phase of the design, and for the second phase we would very much welcome others to get involved with the detailed design and implementation (or join the IHG and contribute further funding). -- Duncan Coutts, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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Execution order in IO
by Jon Schneider 17 Apr '15

17 Apr '15

Good morning all, I think I've got the hang of the way state is carried and fancy operators work in monads but still have a major sticky issue. With lazy evaluation where is it written that if you write things with no dependencies with a "do" things will be done in order ? Or isn't it ? Is it a feature of the language we're supposed to accept ? Is it something in the implementation of IO ? Is the do keyword more than just a syntactic sugar for a string of binds and lambdas ? Jon

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