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[ANN] extended-categories
by Ian Milligan 19 Aug '14

19 Aug '14

extended-categories <github.com/ian-mi/extended-categories> is an implementation of categories designed to make use of GHC's recently enriched kind system. This project is a work in progress (only a few basic constructs are implemented), but your comments are welcomed. extended-categories requires a recent version of GHC (I have only tested it with 7.8.3). Categories are poly-kinded and have an Object constraint family: class Category m where type Object (m :: k -> k -> *) (a :: k) :: Constraint id :: Object m a => m a a (.) :: (Object m a, Object m b, Object m c) => m b c -> m a b -> m a c This means in addition to our usual categories of kind * -> * -> * we can define categories of other kinds, for example (:-) from the constraints package forms a category with kind Constraint -> Constraint -> * (whose instance is used in this package)! Functors are named (tagged) as done in the data-category package. This allows a much wider variety of functors to be defined. Additionally functors must provide proof that they are closed under the object constraint, i.e. forall a. Object (Domain f c1) a :- Object (Codomain f c2) (FMap f a). For any two categories c1: k1 -> k1 -> * and c2: k2 -> k2 -> *, the product category (c1 :><: c2) has kind (k1, k2) -> (k1, k2) -> *. The functor (Diag c) is defined to be the functor from c to c :><: c which sends the object X to '(X, X) and morphism f to the morphism f :><: f. Categories which contain their products (the class ProductCategory) are defined by the universal property described here < http://en.wikipedia.org/wiki/Universal_morphism#Products>, i.e. by a terminal morphism, for every object a and b of c, from (Diag c) to the object '(a, b) of c :><: c. From this terminal morphism, the functions fst, snd, (&&&), and (***), as well as the product functor from c :><: c to c mapping '(a, b) to a >< b and f :><: g to f *** g, are defined. Here are some examples of how this works with the standard Haskell functors: *Functor> fmap (CanonicalF :.: CanonicalF) P.succ [P.Just 2, P.Nothing] [Just 3,Nothing] *Product> fmap (CanonicalF :.: ProductF) ((P.+1) :><: (P.+2)) [(1,2), (3,4), (5,6)] [(2,4),(4,6),(6,8)] or alternatively fmap CanonicalF ((P.+1) *** (P.+2)) [(1,2), (3,4), (5,6)] Next I will likely be adding more instances as well as some documentation. Thanks for reading, Ian Milligan

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Reducing CPU load when using Helm
by Kaspar Emanuel 19 Aug '14

19 Aug '14

Forwarding this to haskell-cafe as it failed before. On 18 August 2014 20:24, Kaspar Emanuel <kaspar.bumke(a)gmail.com> wrote: > Hi, > > are there some simple tricks to reduce the CPU load? This simple > square rendering sits at 20% CPU even when the window size remains > constant. > > import FRP.Helm > import qualified FRP.Helm.Window as Window > > render :: (Int, Int) -> Element > render (w, h) = collage w h [move (100, 100) $ filled red $ square 64] > > main :: IO () > main = do > engine <- startup defaultConfig > run engine $ render <~ Window.dimensions engine > > The binary fractal tree I submitted in another thread on helm-dev > sits at 100% CPU when the mouse isn't moving. It seems to me that > Helm keeps re-drawing and re-computing when it doesn't need to. > > I started digging through the source a bit but it will take me a while > to understand Elerea and how it samples the inputs and causes things > to update. > > Are there any quick fixes? > > Ciao, > > Kaspar

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Is there something for emacs to view project module structure?
by Magicloud Magiclouds 19 Aug '14

19 Aug '14

Hi, I think a structure viewing in editor could be very help for long file or big project. Something like java/c# IDEs do. But I could not find a hint on google. Any suggestions? -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Type-level numbers problem
by Konstantine Rybnikov 18 Aug '14

18 Aug '14

Hi! I wrote one thing with type-level numbers that were represented as simple data Zero data Succ a Then, in order to not invent my own peano numbers, I decided to go look for ones, and found GHC.TypeLits. But unfortunately, it shows a weird error for me. Here is a piece of code: https://gist.github.com/k-bx/a7b49165399658f87358 The one that's below "main" is working properly, while the one on top of it gives this error: typenats.hs:17:16: No instance for (Op D (0 + 1)) arising from a use of `f' Possible fix: add an instance declaration for (Op D (0 + 1)) In the expression: f (VJ i :: VJ D (0 + 1)) In an equation for `f': f (VJ i) = f (VJ i :: VJ D (0 + 1)) In the instance declaration for `Op D 0' Maybe I worked too much on type-level numbers today to not understand this simple error I'm getting, but could someone be so kind and explain me what am I doing wrong? Thank you very much!

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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 17 Aug '14

17 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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local mins
by Закиров Марат 15 Aug '14

15 Aug '14

Some time ago we have a discussion and now I am ready to present my algorithm for counting local mins. It is liniar for imperative case and in functially too (I hope). I spent hours of debugging on it... -- | Main entry point to the application. module Main where str = [5, 6, 7, 1, 0, 5, 3] norm :: ([a],[a]) -> ([a],[a]) norm (x,[]) = (take l1 x, take l2 $ reverse x) where l1 = length x `div` 2 l2 = length x - l1 norm ([],x) = (take l2 $ reverse x, take l1 x) where l1 = length x `div` 2 l2 = length x - l1 norm x = x insert :: (Ord a, Show a) => [a] -> Int -> ([(a, Int)],[(a, Int)]) -> ([(a, Int)],[(a, Int)]) insert [] _ x = x insert x p ([],[]) = ([(head x, p)],[]) insert x p (y,[]) = insert x p (norm (y,[])) insert x p (ys,z:zs) = if head x >= fst z then (ys,(head x, p):z:zs) else insert x p (ys,zs) delete :: (Ord a, Show a) => Int -> Int -> ([(a, Int)],[(a, Int)]) -> ([(a, Int)],[(a, Int)]) False = undefined delete p r ([],x) = delete p r (norm ([],x)) delete p r (x:xs,y) = if p > (snd x + r) then (xs,y) else (x:xs,y) getmin :: (Ord a, Show a) => ([(a, Int)],[(a, Int)]) -> a getmin ([],[]) = error "Getmin error" getmin ([],x) = getmin (norm ([],x)) getmin (x:xs,y) = fst x pass :: (Ord a, Show a) => [a] -> [a] pass [] = [] pass (x:xs) = xs minn :: Ord a => [a] -> [a] -> [a] minn x y = [] lmini :: (Ord a, Show a) => Int -> Int -> ([(a, Int)],[(a, Int)]) -> [a] -> [a] -> [a] lmini _ _ _ [] _ = [] lmini p r deq c l = if p < r then lmini (p+1) r (insert l p deq) c (pass l) else getmin deqn : lmini (p+1) r deqn (pass c) (pass l) where deqn = if p < (r*2) then insert l p deq else insert l p (delete (p-1) r deq) lmin :: (Ord a, Show a) => Int -> [a] -> [a] lmin r x = lmini 0 r ([],[]) x x main :: IO () main = do putStrLn "Min for list" putStrLn $ show str -- Regards, Marat. С уважением Марат.

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ANNOUNCE: BOB Conference 2015 Berlin
by Matthias Fischmann 15 Aug '14

15 Aug '14

BOB Conference 2015 Berlin 23.1.2015 http://bobkonf.de/2015/ CALL FOR CONTRIBUTIONS English: http://bobkonf.de/2015/cfp.html German: http://bobkonf.de/2015/cfp.html Deadline: September 30, 2014 You drive advanced software engineering methods, implement ambitious architectures and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer you a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! We are looking for talks about best-of-breed software technology, e.g.: - functional programming - reactive programming - micro-service architectures - persistent data structures and databases - everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. This could take the form of e.g.: - experience reports - introductory talks on technical background - demos and how-tos We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. - questions to bobkonf at active minus group dot de - proposal deadline: September 30, 2014 - notification: October 15, 2014 - program: October 2014, 2014 For more info, visit http://bobkonf.de/2015/ Looking forward to your submissions, and to seeing you there! cheers, matthias

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Functional Programming Job Opportunities
by stephen.t.west＠barclays.com 15 Aug '14

15 Aug '14

The Risk & Analytics team at Barclays currently has opportunities for functional programmers with experience of investment banking technology and quantitative analytics. If you're interested, please contact me (stephen dot t dot west at barclays dot com). Regards, Stephen. _______________________________________________ This message is for information purposes only, it is not a recommendation, advice, offer or solicitation to buy or sell a product or service nor an official confirmation of any transaction. It is directed at persons who are professionals and is not intended for retail customer use. Intended for recipient only. This message is subject to the terms at: www.barclays.com/emaildisclaimer. For important disclosures, please see: www.barclays.com/salesandtradingdisclaimer regarding market commentary from Barclays Sales and/or Trading, who are active market participants; and in respect of Barclays Research, including disclosures relating to specific issuers, please see http://publicresearch.barclays.com. _______________________________________________

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Using `jack` on Windows, sounds realistic?
by Alois Cochard 15 Aug '14

15 Aug '14

Hi all, I've been recently used the great `jack` library from Henning Thielemann (cc'ed) on my linux computer. It work like a charm, but I was wondering about Windows support? As I see Jack run on windows, I'm hoping I might be able to build my haskell application that use `jack` on windows as well, is that realistic? anyone have tried already? Thanks in advance Note: I plan to have an other backend using 'portaudio', which would allow me to be cross-platform anyway... but using Jack bring ASIO support, which is really need for my use case (real time synthesizer). -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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Cannot install the Haskell Platform on GNU/Linux (possible Cabal issue)
by egarrulo 15 Aug '14

15 Aug '14

Hello guys, I cannot install the Haskell Platform 2014.2.0.0 on my GNU/Linux system: $ ./platform.sh \ > --prefix=/opt/haskell-platform/haskell-platform-2014.2.0.0 \ > ../ghc-7.8.3/ghc-7.8.3-i386-unknown-linux.tar.bz2 Warning: The following packages are likely to be broken by the reinstalls: haskell-platform-2013.2.0.0 Use --force-reinstalls if you want to install anyway. === pre-requisite packages for hptool are not installed run the following: cd hptool ; cabal install --only-dependencies However, the dependencies for *hptool* are already installed: $ cd hptool ; cabal install --only-dependencies Resolving dependencies... All the requested packages are already installed: Use --reinstall if you want to reinstall anyway. The existing Haskell system: - GHC 7.6.3 - Haskell Platform 2013.2.0.0 - cabal-install 1.16.0.2 (using Cabal library 1.16.0) Any help? Thank you.

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How to improve the zipwith's performance
by jun zhang 15 Aug '14

15 Aug '14

Dear All I write a code for Clustering with Data.Clustering.Hierarchical, but it's slow. I use the profiling and change some code, but I don't know why zipwith take so many time? (even I change list to vector) My code is as blow, Any one kindly give me some advices. ====================== main = do .... let cluster = dendrogram SingleLinkage vectorList getVectorDistance .... getExp2 v1 v2 = d*d where d = v1 - v2 getExp v1 v2 | v1 == v2 = 0 | otherwise = getExp2 v1 v2 tfoldl d = DV.foldl1' (+) d changeDataType:: Int -> Double changeDataType d = fromIntegral d getVectorDistance::(a,DV.Vector Int)->(a, DV.Vector Int )->Double getVectorDistance v1 v2 = fromIntegral $ tfoldl dat where l1 = snd v1 l2 = snd v2 dat = DV.zipWith getExp l1 l2 ======================================= build with ghc -prof -fprof-auto -rtsopts -O2 log_cluster.hs run with log_cluster.exe +RTS -p profiling result is log_cluster.exe +RTS -p -RTS total time = 8.43 secs (8433 ticks @ 1000 us, 1 processor) total alloc = 1,614,252,224 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc getVectorDistance.dat Main 49.4 37.8 tfoldl Main 5.7 0.0 getExp Main 4.5 0.0 getExp2 Main 0.5 1.5

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HaskellWiki page about SDL
by Henk-Jan van Tuyl 14 Aug '14

14 Aug '14

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 -- 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 (and beyond) in education
by Rustom Mody 14 Aug '14

14 Aug '14

I am collecting some data on FP used to introduce programming ie as a first course: http://blog.languager.org/2014/08/universities-starting-functional.html Naturally the haskell link is the first: http://www.haskell.org/haskellwiki/Haskell_in_education I was just wondering if there are more extremal cases of this: eg Are there any univs using Idris/Agda to *introduce* programming/math/proofs etc

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maintainer needed: extensible-effects
by Ben Foppa 14 Aug '14

14 Aug '14

Hey cafe, is there anybody interested in taking over maintainership of the extensible-effects package? I'm rather busy and not keeping a good eye on it.

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Closed Type Family Simplification
by Ian Milligan 14 Aug '14

14 Aug '14

When a closed type family has only one instance it seems like it should never fail to simplify. Yet this doesn't appear to be the case. When I defined (in GHC 7.8.3) the closed type family type family (:.:) f g a where (:.:) f g a = f (g a) I get errors such as 'Could not deduce (Object c3 ((:.:) f g a) ~ Object c3 (f (g a)))' (where Object is a Constraint family), indicating that f (g a) is not being substituted for (:.:) f g a as desired. Any idea why this happens?

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Does the lambda calculus have provisions for I/O? State can be done with free variables.
by KC 14 Aug '14

14 Aug '14

Hi: Does the lambda calculus have provisions for I/O? State can be done with free variables. -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

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ANNOUNCE: hayland 0.1.0.0
by Auke Booij 14 Aug '14

14 Aug '14

I just pushed the first release of the Haskell bindings to Wayland I've been working on to Hackage. SHAMELESS SPAM ----- I'm looking for a PhD position in (mathematical) type theory (preferably in Europe). Contact me for my (interesting!) background. What is Wayland? ----- For those of you who have been living under a rock, X11 is probably going to be ditched soon (porting work for GNOME, KDE, and E is already well underway), and the graphics stack reworked, in favor of "wayland". There will no longer be a monolithic server between the compositor (aka window manager) and the window clients. In the new design, the compositor *is* the central server. The new architecture allows for proper isolation of clients (a HUGE security improvement over X11), as well as major cleanups of code (enabling embedded use). Why bind to C code? ----- In theory, wayland should only be a protocol specification (which happens to have a reference implementation) which could be implemented in Haskell. However, the current state of the matter is that for EGL implementation reasons, one is forced to bind to this reference implementation. (More precisely, the EGL libraries need to be able to configure wayland - and such code would have to be written for every wayland implementation.) So in practice, one can't write a pure Haskell implementation, and that's why I made bindings for the C library. Where's the code? ----- https://github.com/tulcod/haskell-wayland Wait, why are you even binding to Wayland? ----- Not sure, but it's pretty foundational stuff so I'm sure it'll be of use to someone, somewhere. Maybe someone wants to write a window manager for the new ecosystem (I'm looking at you XMonad)? Wow, I've never seen a module expose this many symbols ----- Yes, if anyone has ideas on how to reorganize and/or clean up the symbols exposed by the various part of the library, I am most interested. The problem here is that I'm generating a lot of code using template haskell, and TH does not give you control over which symbols you want to expose and how. I could write this list to a haskell source file at configure time instead (which might be useful for other reasons as well), but ideally I would like to split up the library into the various "interfaces" wayland offers - but these interfaces are unknown at dev time time, and I don't think there is remotely any mechanism to generate /modules/ at compile time. I'm interested to hear what you guys think about controlling the symbol exposure of TH-generated code. TemplateHaskell /and/ GeneralizedNewtypeDeriving? Are you /trying/ to derive bottom? ----- Well I sacrificed some Safety in favor of exposing nice Haskelly types. Feedback is welcome. Final note ----- By the way, I also wrote bindings to xkbcommon a while ago, although they need some attention. Anyway, my point is that with hayland and xkbcommon in place (both in a semi-usable state), there should be plenty of groundwork ready for you to get started with Wayland on Haskell. (xkbcommon is the de facto standard library to work with keyboard layouts in wayland. It translates keyboard events ("which key did you press") into Unicode symbols ("what letter should appear on the screen"), using the right keyboard layout.)

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Visualising Haskell function execution
by Jan Paul Posma 13 Aug '14

13 Aug '14

Hey all, Last weekend my friend Steve and I did a small project for visualising Haskell function execution in the browser. It's meant to be used in education, and uses a tiny custom parser. I figured it could be of interest for anyone here learning or teaching Haskell: https://stevekrouse.github.io/hs.js/ To see it in action, scroll a bit down to the red bordered box, and click on "map", and then keep clicking on each new line. I hope it can be useful to someone. Cheers, JP

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Openings for brilliant Haskell devs for exciting project "as close to a space station as you can get" @ Swedish spinoff, DSLs/safety-critical/embedded software, and more
by Johan Glimming 13 Aug '14

13 Aug '14

Dear All, I’d like to share this exciting job opportunity (formatted text below), as this forum might be right for the very skilled developers we are looking for here. The LinkedIn posting is on the following webpage, e.g. in case the email does not display correctly: https://www.linkedin.com/today/post/article/20140812174919-547525-openings-… … Best wishes, Johan Glimming @ LinkedIn: http://se.linkedin.com/in/glimming — Openings for brilliant Haskell devs for exciting project "as close to a space station as you can get" @ Swedish spinoff, DSLs/safety-critical/embedded software, and more As we grow our business further we look for extraordinary Haskell developers to further strengthen our exceptionally skilled teams in our spinoff and startup Functor Group AB, Kista/Stockholm, Sweden, with subsidiaries. www.functorgroup.com @functors +FunctorGroups You would have an impressive background in computer science, with industrial experience and first-class academic education including certainly advanced functional programming. Compiler design skills are valued highly. Experience of static code analysis (tools and/or research) and safety-critical software and embedded software development are all relevant to this startup and spinoff. You would be part of a team with extraordinary skills and work with other talented individuals which, for those with the right mindset, is extremely rewarding. It's relevant with skill sets that include AFP, EDSLs, type systems, Martin-Löf type theory, dependent types, formal methods, standard-type static analysis tools (as we offer a new kind that adds dependent types to the abstract interpretation approach), experience from tools form e.g. Coverity, Klocwork, MathWorks,, Spec#, Coq, Agda, Epigram, Twelf or other such tools, LLVM, ANSI / ISO C, MISRA C, software testing, various programming languages and their implementation, domain-specific languages, DDD, language-based programming turned into our emerging method named language-driven development, logical frameworks, meta languages, operational semantics, logic, theorem provers. (Learn more atwww.functor.se.) You should be able to contribute to very demanding, challenging, creative teamwork as it manifests itself in a pioneering high-tech spinoff. This all means great responsibility, important contributions to be made, with multiple and varying roles in our highly dynamic work environment where you would be working with other exceptional talents and contribute with your passion for functional programming. You are assumed to share our enthusiasm for and commitment to the new constructive programming paradigm, and recognise the value and great importance of our research foundation, our core technology, being made available in the industry. You would share and nourish our vision for the future of the software industry with the new constructive programming paradigm based on type theory research and the next level of functional programming with EDSL integrated in programming as never done before. But most important is of course your documented talent and experience in Haskell development at an industrial level as well as great teamwork skills and enthusiasm about relevant technologies, and being aligned with our mission (for which see www.functorgroup.com) Several of our developers have higher academic degrees such as a PhD in computer science, logic or mathematics, including two of our Research Engineers, who are professors. (and two more in our Advisory Board, both with own spinoffs, plus an extensive network to leading researchers that we work closely with now and in the future). Your experience may include software development in segments such as safety-critical software and embedded software, hardware modelling, advanced DSL implementation, compiler design and compiler technologies, GPU applications, implementing software testing tools and tools for formal methods. We do not expect you to have all these listed skills, but we expect you to be exceptionally talented and contribute to the success and further growth of Functor Group and its subsidiaries. We are now in an extremely interesting but demanding phase as a spinoff eg with one extraordinarily high-profile customer. You will be part of that project and other very exciting customer projects where we deploy unmatched new technology that brings a new programming paradigm to the software industry, with customers internationally, and an exciting journey into a future where research progress is finally bring aligned with best-practices also in software engineering in a world where software drives innovation and much of growth, but where our technology opens up for much needed improvements in the way software is being developed, designed and tested. Mail your application with resumé with references etc to jobs(a)functor.se. www.functorgroup.com Posted by Dr Johan Glimming at Functor Group AB and Functor AB —

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ANNOUNCE: wxHaskell 0.91.0.0
by Henk-Jan van Tuyl 12 Aug '14

12 Aug '14

L.S., I am happy to announce a new version of wxHaskell. This version binds to both wxWidgets 2.9 and 3.0 [0]. As wxWidgets 3.0 is significantly better, I advice everyone, who is already using wxHaskell, to upgrade to wxWidgets 3.0.1 What is it? ----------- wxHaskell[1] 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? ----------- - Accept both wxWidgets 2.9 and 3.0, with a preference for 3.0 - Added bindings for wxGraphicsContext::CreatePath - Use the same custom hook for `cabal copy` in wxc/Setup.hs - Many updates in definitions of constants and some 'deprecated' annotations - samples/wx/TestTaskBarIcon.hs now displays an icon in the taskbar - Parsec.hs can now handle lines starting with "//" properly (package wxdirect) - Fixed build issue that was caused by not having both the 2.9 and 3.0 versions of wxWidgets installed - Made samples/test/STCEvent.hs compilable - Solved warnings about deprecated methods and duplicate constant definition - Added -Wl to options for compiling wxc.dll - Adapted upper limit for packages process and array - Solved "deprecated" warning from GHC 7.8.2 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 [1] https://www.haskell.org/haskellwiki/WxHaskell -- 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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Updating code to work with vinyl 0.4
by Mateusz Kowalczyk 12 Aug '14

12 Aug '14

Hi, I'm looking for some help in helping to migrate to vinyl-0.4 from earlier version. I'll first outline how I currently have things set up and then ask a few questions. For reference the whole project is at [1]. You can just skip to questions in the end if you want to. I have a small project which goes out to a few sites, fetches some similar XML data, parses some fields and returns a data type. My original attempt was to generate a data type per site but that was very ugly: couldn't reuse functions, accessors, anything. So I then turned to vinyl and have the following solution: I have a bunch of common fields defined like this: -- file_url ∷ "file_url" ::: String file_url = Field parent_id ∷ "parent_id" ::: Maybe Integer parent_id = Field -- and so on. I'm using HXT to process the XML I get from each site so I have created many HXT arrows creating each field like this: -- parent_idA ∷ (Functor (cat XmlTree), ArrowXml cat) ⇒ cat XmlTree (PlainRec '["parent_id" ::: Maybe Integer]) parent_idA = (parent_id =:) . readMaybe <$> getAttrValue "parent_id" -- Then for each site I define records like this -- type GelbooruPost = PlainRec '[ "height" ::: Integer , "score" ::: Integer , "file_url" ::: String , "parent_id" ::: Maybe Integer , … ] -- and create the final HXT arrow which will parse and run my value parsers on the whole output -- parsePost ∷ (Functor (cat XmlTree), ArrowXml cat) ⇒ cat XmlTree GelbooruPost parsePost = hasName "post" >>> heightA <:+> scoreA <:+> file_urlA <:+> parent_idA <:+> sample_urlA <:+> sample_widthA <:+> sample_heightA <:+> preview_urlA <:+> ratingA <:+> tagsA <:+> idA <:+> widthA <:+> changeA <:+> md5A <:+> creator_idA <:+> has_childrenA <:+> created_atA <:+> statusA <:+> sourceA <:+> has_notesA <:+> has_commentsA <:+> preview_widthA <:+> preview_heightA -- This works OK: I have similar records for each site and vinyl let me use the same accessors to work over the data from each site without much hassle even though they all return slightly different things. But now vinyl-0.4 is out and I have to update but I'm struggling. As per tutorial I converted all my fields to this format: -- data Fields = Height | Score | FileUrl | ParentId | SampleUrl | … -- Then generated singletons and made universe: -- genSingletons [ ''Fields ] makeUniverse' ''Fields "ElF" semantics ''ElF [ 'Height :~> ''String , 'Score :~> ''Integer , 'FileUrl :~> ''String , 'ParentId :~> ''Integer -- Maybe Integer , 'SampleWidth :~> ''Integer , 'SampleHeight :~> ''Integer , 'PreviewUrl :~> ''String , 'Rating :~> ''Rating , 'Tags :~> ''String -- [String] -- As you can see I have a problem here already: I don't know how to specify ‘Maybe Integer’ or ‘[String]’ in the way that is accepted. Previously I would just do "tags ::: [String]" and it worked. I also wonder what things like: -- PlainRec '["parent_id" ::: Maybe Integer]) -- now become. “PlainRec ElF (ParentId ': '[])” works but is ugly, is there a shorthand for singletons? This is assuming I can convince the ParentId field to be Maybe Integer. Lastly I'd like to know why trivial examples such as this -- a ∷ PlainRec ElF (Score ': '[]) a = SScore =: 7 -- require a type signature. While I put down the signatures anyway, I wonder if there's a way to skip them. I suppose using the field in an annotated record somewhere might let me do this. I imagine the problem here is that we need to specify ElF. Perhaps I am meant to approach this whole thing differently which is why I laid out the structure a bit rather than just asking about syntax. I have watched the video at [2] and while the new records do sound better, I can't find a good guide on how to use them. The tutorial on GitHub[3] is rather lacking. If someone knows about more guides then I'd love to hear about that too. Thanks! [1]: http://github.com/Fuuzetsu/h-booru [2]: http://vimeo.com/102785458 [3]: https://github.com/VinylRecords/Vinyl/blob/master/tests/Intro.lhs -- Mateusz K.

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HGamer3D - version 0.4
by Peter Althainz 12 Aug '14

12 Aug '14

You will find version 0.4 of HGamer3D on github and hackage now. It also comes with some updated introductions on http://www.hgamer3d.org . best regards Peter (uotbw)

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Any tips on "doing it right" for a small program?
by Bram Neijt 12 Aug '14

12 Aug '14

Dear reader, I'm still new to haskell, and decided to convert a simple bash script to a full-on-bells-and-whistles Haskell program (as a learning experience). As you might guess I could use some help. The program is very simple, in Bash it reads: CMDPATTERN="$@" while [[ "`pgrep --count --full "$CMDPATTERN"`" -gt 1 ]]; do sleep 5 done AKA: while there is a command running with the given string, loop. I called this script "after" and use it on the commandline to chain commands from different terminals. The Haskell version is available at https://github.com/bneijt/after What I have done: - Add Travis CI - Add a first test case using test-framework - Add commandline option parsing using "options" - Implement a fork-join behavior using parallel-io What I would like help with: - How to add a --version that reflects the after.cabal version? - Is there a library for what I'm doing in Process.hs (listing running processes, etc.)? - How to add "-p <pid>" support, so I can do "after -p 129 -p 402" (after both pids) - Should I move from exitcode-stdio-1.0 to detailed-1.0? - Any and all other hints you might have Also if you have projects you want to point to for inspiration, I'd be happy to take a look. Greetings, Bram

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New Functional Programming Job Opportunities
by Functional Jobs 11 Aug '14

11 Aug '14

Here are some functional programming job opportunities that were posted recently: Big Data Engineer / Data Scientist at Recruit IT http://functionaljobs.com/jobs/8731-big-data-engineer-data-scientist-at-rec… Cheers, Sean Murphy FunctionalJobs.com

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Irritating Referential Transparency behavior?
by martin 10 Aug '14

10 Aug '14

Hello all, I came across something strange: This code compiles: ------------------------------------------------------------ data LProcess a = LP {lstep :: Writer [String] (Event a -> ([Event a], LProcess a))} ------------------------------------------------------------ exProcess2 :: ProcState -> Location -> LProcess EvtData exProcess2 pState loc = LP {lstep = xxx} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc but when I replace xxx by myStep pState as in exProcess2 pState loc = LP {lstep = myStep pState} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc I get No instance for (Monad m0) arising from a use of `myStep' The type variable `m0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) It compiles again when I remove the xxx = line. Why is that so?

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Get out structured data from a C/C++ library in Haskell
by Nicola Gigante 10 Aug '14

10 Aug '14

Hello everybody. I'm new to the list so I'd like to say hello to you. I'm a student of computer science and early practitioner of Haskell. I've decided to implement the next project in Haskell but I need to interface a C++ library. I've read all the wikis material about the matter and I have an understanding of how FFI to C works in general. The library in question is a SAT solver for LTL formulas, and all I need to do is to be able to create the AST of the formula (Haskell will do the parsing) and pass it to the library, and then get back the reply. From the C++ point of view, the AST of the formulas consists simply of objects linked together with raw pointers. Nodes are of the same type, with an internal enum that specifies the type of node, so it's not an inheritance hierarchy or fancy things... What I would like to do is to be able to declare an algebraic data type that represents the AST and somehow mangle it to a form that can be passed to the C++ function of the library (that I can wrap into an extern "C" function to be able to use it through FFI if needed). How can I do that? In general, I've only seen example of how to exchange primitive types with C functions through the FFI, but not for example structures or pointers to structures. Note that I have control over the source code of the C++ library too, so the question includes suggestions about how to structure the C++ data as well, to ease the integration. Thank you for your help, Nicola

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ANN: immortal-0.1
by Roman Cheplyaka 10 Aug '14

10 Aug '14

I am pleased to announce the first release of the "immortal" package. Immortal allows you to create threads that never die. If the action executed by such a thread finishes or is killed by an exception, it is automatically restarted. Such a behavior is often desired when writing servers, so I decided to release a package that does exactly that. http://hackage.haskell.org/package/immortal https://github.com/feuerbach/immortal Roman

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Haskell Platform 2014.2.0.0 is Released!
by Mark Lentczner 09 Aug '14

09 Aug '14

On behalf of the Haskell Platform team, I'm happy to announce the release of *Haskell Platform 2014.2.0.0* featuring: GHC 7.8.3 53 packages 860+ public modules 4 tools This release features a major upgrade to OpenGL and GLUT. In addition, "behind the scenes", this release of the platform is produced with a new build system, and many improvements to the installations on all three OS families. Get it now: Download Haskell Platform <http://www.haskell.org/platform/> — for Windows <http://www.haskell.org/platform/windows.html> — for Mac OS X <http://www.haskell.org/platform/mac.html> — for Linux <http://www.haskell.org/platform/linux.html> (and similar systems) N.B.: You may need to explicitly re-fresh those links when visiting in your browser - those pages tend to get cached for very long periods of time. — Mark "platform wrangler" Lentczner P.S.: I realize this one was a long time a'comin'. I take the responsibility for the decisions that lead up to being this late, including deciding it was worth it to wait for GHC 7.8, and that this was the right time to re-write the platform build system. I hope the speed that we can now turn the platform will be evident in future releases. Haskell Platform is created by a team of many hands. Special call out to Randy Polen for the new Windows build, and Yitzchak Gale and Neil Mitchell for help with the new build system. Thanks also to all the intrepid folks that tried out the early alphas and release candidates. Additional help is always welcome!

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Free monad based EDSL for writing LLVM programs.
by arrowdodger 09 Aug '14

09 Aug '14

Hello. I'm new with Haskell and FP, so i wanted someone to give comments on the package i've made [1]. It's, actually, my first attempt to create something more or less real, so any feedback would be welcome. I've used Free monad to create EDSL that allows writing LLVM IR code. Afterwards it could be converted into pure AST structure provided by llvm-general-pure[2] package. Currently, it supports almost every instruction, but i haven't yet come up with sensible defaults for them. Another thing that bugs me is the ability to transform the code in syb way. I want take a user-supplied function that would pattern-match instruction and produce another code block and apply this function everywhere in the code, but still can't get my head around it. I've come up with extF function, that unlike extM, would resort to wrap instead of return, but that's all i've managed to do. Thanks in advance. [1] https://bitbucket.org/arrowdodger/llvm-general-edsl [2] http://hackage.haskell.org/package/llvm-general-pure

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Re: [Haskell-cafe] Free monad based EDSL for writing LLVM programs.
by Matt Giles 08 Aug '14

08 Aug '14

For transforming the code, have you checked out the uniplate package? It seems like it could fit your problem pretty well. On 8 August, 2014 at 5:00:19 AM, haskell-cafe-request(a)haskell.org (haskell-cafe-request(a)haskell.org) wrote: Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. Re: Side-by-side pretty printing (J. Waldmann) 2. Free monad based EDSL for writing LLVM programs. (arrowdodger) 3. parsec: problem combining lookAhead with many1 (bug?) (silly8888) 4. Re: parsec: problem combining lookAhead with many1 (bug?) (Andreas Reuleaux) 5. Performance of StateT and best practices for debugging (Kyle Hanson) 6. [ANN] rtorrent-state 0.1.0.0 (Mateusz Kowalczyk) 7. Re: Performance of StateT and best practices for debugging (John Lato) 8. How to improve the zipwith's performance (jun zhang) 9. Re: Performance of StateT and best practices for debugging (Bardur Arantsson) 10. Visualising Haskell function execution (Jan Paul Posma) 11. Re: Performance of StateT and best practices for debugging (John Lato) ---------------------------------------------------------------------- Message: 1 Date: Thu, 7 Aug 2014 12:33:43 +0000 (UTC) From: J. Waldmann <waldmann(a)imn.htwk-leipzig.de> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Side-by-side pretty printing Message-ID: <loom.20140807T142947-462(a)post.gmane.org> Content-Type: text/plain; charset=us-ascii This is what I use http://autolat.imn.htwk-leipzig.de/gitweb/?p=autolib;a=blob;f=todoc/Autolib… it's of the works-but-looks-ugly-and-is-terribly-inefficient variety but since it's applied to small Docs only (like, columns of matrices), I don't really care. - J.W. ------------------------------ Message: 2 Date: Thu, 7 Aug 2014 18:16:57 +0400 From: arrowdodger <6yearold(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Free monad based EDSL for writing LLVM programs. Message-ID: <CALH631=EbZ8aTZi=oPdfsP97J2XrRCTf=DpX+uaZ5m9=0mxXhw(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hello. I'm new with Haskell and FP, so i wanted someone to give comments on the package i've made [1]. It's, actually, my first attempt to create something more or less real, so any feedback would be welcome. I've used Free monad to create EDSL that allows writing LLVM IR code. Afterwards it could be converted into pure AST structure provided by llvm-general-pure[2] package. Currently, it supports almost every instruction, but i haven't yet come up with sensible defaults for them. Another thing that bugs me is the ability to transform the code in syb way. I want take a user-supplied function that would pattern-match instruction and produce another code block and apply this function everywhere in the code, but still can't get my head around it. I've come up with extF function, that unlike extM, would resort to wrap instead of return, but that's all i've managed to do. Thanks in advance. [1] https://bitbucket.org/arrowdodger/llvm-general-edsl [2] http://hackage.haskell.org/package/llvm-general-pure -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/6d973f16…> ------------------------------ Message: 3 Date: Thu, 7 Aug 2014 15:25:23 +0100 From: silly8888 <silly8888(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] parsec: problem combining lookAhead with many1 (bug?) Message-ID: <CAMmzbfWA9S3YGjJ1iQaa72rKZyuV4psvEP3LsQuDGC3QED-YVw(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Suppose that we have the following parser: p = lookAhead (char 'a') >> char 'b' If we use it like so parse p "" "a" we get the following error: Left (line 1, column 1): unexpected "a" expecting "b" What happened is that char 'a' succeeded by consuming the 'a' from the input and then lookAhead rewinded the input stream (as it does on success). Then, char 'b' tries to parse (again) the first character of the input and fails. Everything works as expected. Now let's slightly modify our parser: p' = lookAhead (many1 $ char 'a') >> char 'b' I've only added a many1. I was expecting this parser to give the same error as the previous one: many1 $ char 'a' will succeed consuming one 'a' and then lookAhead will rewind the input (as it does on success). Thus when we call char 'b' we are going to be in the beginning of the input again. Well, that doesn't happen: Left (line 1, column 2): unexpected end of input expecting "b" As you can see, lookAhead did not rewind the input as it was supposed to. ------------------------------ Message: 4 Date: Thu, 07 Aug 2014 17:32:11 +0100 From: Andreas Reuleaux <reuleaux(a)web.de> To: silly8888 <silly8888(a)gmail.com> Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] parsec: problem combining lookAhead with many1 (bug?) Message-ID: <87y4v0z2es.fsf(a)web.de> Content-Type: text/plain While I haven't tried out your example in parsec, I can at least confirm that in trifecta it does work that way you expect it, ie. there is no difference between the error messages in both of your cases: (parsec's many1 = trifecta's some) Prelude > :m +Text.Trifecta Prelude Text.Trifecta > :m +Text.Parser.LookAhead Prelude Text.Trifecta Text.Parser.LookAhead > ... Prelude Text.Trifecta Text.Parser.LookAhead > parseTest (lookAhead (char 'a') >> char 'b') "a" ... Loading package reducers-3.10.2.1 ... linking ... done. Loading package trifecta-1.5.1 ... linking ... done. (interactive):1:1: error: expected: "b" a<EOF> ^ Prelude Text.Trifecta Text.Parser.LookAhead > parseTest (lookAhead (some $ char 'a') >> char 'b') "a" (interactive):1:1: error: expected: "b" a<EOF> ^ Prelude Text.Trifecta Text.Parser.LookAhead > Hope this helps. -Andreas silly8888 <silly8888(a)gmail.com> writes: > Suppose that we have the following parser: > > p = lookAhead (char 'a') >> char 'b' > > If we use it like so > > parse p "" "a" > > we get the following error: > > Left (line 1, column 1): > unexpected "a" > expecting "b" > > What happened is that char 'a' succeeded by consuming the 'a' from the > input and then lookAhead rewinded the input stream (as it does on > success). Then, char 'b' tries to parse (again) the first character of > the input and fails. Everything works as expected. > > Now let's slightly modify our parser: > > p' = lookAhead (many1 $ char 'a') >> char 'b' > > I've only added a many1. I was expecting this parser to give the same > error as the previous one: many1 $ char 'a' will succeed consuming one > 'a' and then lookAhead will rewind the input (as it does on success). > Thus when we call char 'b' we are going to be in the beginning of the > input again. Well, that doesn't happen: > > Left (line 1, column 2): > unexpected end of input > expecting "b" > > As you can see, lookAhead did not rewind the input as it was supposed to. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ Message: 5 Date: Thu, 7 Aug 2014 10:57:47 -0700 From: Kyle Hanson <me(a)khanson.io> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAMJUouBqFbSi+ifFsbYdXpba7pPVoP8BkyZxZaUoqLNuHc7VzQ(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hello, I was looking at cleaning up my refactoring a core loop of template rendering to go from a loop with many parameters loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] -> ExceptT StrapError m Builder to a looped state monad transformer loop :: [Pieces] -> RenderT m Builder newtype RenderT m a = RenderT { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a } deriving ( Functor, Applicative, Monad, MonadIO ) data RenderState m = RenderState { position :: SourcePos , renderConfig :: RenderConfig , blocks :: BlockMap , bucket :: InputBucket m } however, there is a big slow down (about 6-10x) using a StateT. I think it might have something to do with laziness but I am not exactly sure of where to begin in tracking it down. Swapping out the Lazy State to a Strict State helps a little (only a 5x slow down) You can find some of the processing code here: https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… With my old loop commented out. Its messy right now since I am just trying a number of different approaches. I did some more work factoring out the lifts, trying different iterations of foldlM and stuff but that didn't have that much of an effect on performance. After profiling I see in the StateT, the report has a lot more CAFs and garbage collecting. Here is the profiling report from my original version w/o StateT http://lpaste.net/108995 Slow version with StateT http://lpaste.net/108997 Here is the "makeBucket" function that is referenced (it is the same in both state and nonstate): https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… Looking at stacked overflow and the official docs I have gotten an idea of what is going on. The heaps generated between them tells me that a lot more memory is being allocated to lists. These heaps were generated running my render function against a template with nested loops and a list of elements. http://imgur.com/a/2jOIf I am hoping that maybe someone could give me a hint at what to look at next. I've played around with Strictness and refactoring loops to no avail and now am kind of stuck. Any help would be appreciated. -- Kyle Hanson -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/a82b99f5…> ------------------------------ Message: 6 Date: Thu, 07 Aug 2014 21:07:02 +0200 From: Mateusz Kowalczyk <fuuzetsu(a)fuuzetsu.co.uk> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] [ANN] rtorrent-state 0.1.0.0 Message-ID: <53E3CE56.6090500(a)fuuzetsu.co.uk> Content-Type: text/plain; charset=windows-1252 Hi, rtorrent-state is a library that allows working with rtorrent state files (SOMEHASH.torrent.rtorrent) placed in your session directory. If you're an rtorrent user and ever had to manually muck around with those files, you should be able to use this library to make your life easier. For example, you can stop all torrents in your session directory with just: ?overFilesIn "rtorrent/session/dir" stopTorrent? The way it works is by parsing the session files, modifying the resulting data type and serialising it back into the file. I did not do optimisation but I had no problem with test sample of 100,000 files. I need to add IOException handling and maybe extra utility functions but otherwise I consider the library finished. Thanks -- Mateusz K. ------------------------------ Message: 7 Date: Thu, 7 Aug 2014 15:39:53 -0700 From: John Lato <jwlato(a)gmail.com> To: Kyle Hanson <me(a)khanson.io> Cc: haskell-cafe <haskell-cafe(a)haskell.org> Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAJ727GjPpMn3xMDs=4EmJGG0FpndsBwvq5Zkc97X6yQ-H21KEA(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" I haven't looked very closely, but I'm suspicious of this code from "instance Block Piece" ListLike l -> forM l (\obj -> ...) >>= (return . mconcat) The "forM" means that "l" will be traversed once and create an output list, which will then be mconcat'd together. The list has to be created because of the monadic structure imposed by forM, but if the result of the mconcat isn't demanded right away it will be retained as a thunk that references the newly-created list. I'd suggest that you replace it with something like ListLike l -> foldM (\(!acc) obj -> ... >>= return . mappend acc) mempty l Here I've justed added a bang pattern to the accumulator. If whatever is being returned has some lazy fields, you may want to change that to use deepseq instead of a bang pattern. Also, "foo >>= return . bar" is often regarded as a bit of a code smell, it can be replaced with "bar <$> foo" or "bar `liftM` foo", or sometimes something even simpler depending on circumstances (but IMHO sometimes it's more clear to just leave it alone). The heap profile does look like a space leak. The line <StrappedTemplates-0.1.1.0:Text.Strapped.Render.sat_sc1z> is a thunk (you can tell because it's in '<>' brackets), so whatever is referencing that is not strict enough. Sometimes another heap profile report, e.g. "-hc" or maybe "-hy" will give more useful information that lets you identify what exactly "sat_sc1z" is. You could also try compiling with -ddump-stg, which will dump the intermediate STG output which usually shows those names. But then you'll probably also need to re-run the profile, since the names change between compilations. Also IIRC some of values aren't named until the cmm phase, but that's harder to map back to Haskell so if you can identify the code from stg it's simpler. If you haven't seen http://blog.ezyang.com/2011/06/pinpointing-space-leaks-in-big-programs/, I'd highly recommend it if you need to track down a space leak. John L. On Thu, Aug 7, 2014 at 10:57 AM, Kyle Hanson <me(a)khanson.io> wrote: > Hello, > > I was looking at cleaning up my refactoring a core loop of template > rendering to go from a loop with many parameters > > loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] > -> ExceptT StrapError m Builder > > to a looped state monad transformer > > loop :: [Pieces] -> RenderT m Builder > > newtype RenderT m a = RenderT > { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a > } deriving ( Functor, Applicative, Monad, MonadIO ) > > data RenderState m = RenderState > { position :: SourcePos > , renderConfig :: RenderConfig > , blocks :: BlockMap > , bucket :: InputBucket m > } > > however, there is a big slow down (about 6-10x) using a StateT. I think it > might have something to do with laziness but I am not exactly sure of where > to begin in tracking it down. Swapping out the Lazy State to a Strict State > helps a little (only a 5x slow down) > > You can find some of the processing code here: > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > With my old loop commented out. > > Its messy right now since I am just trying a number of different > approaches. I did some more work factoring out the lifts, trying different > iterations of foldlM and stuff but that didn't have that much of an effect > on performance. > > After profiling I see in the StateT, the report has a lot more CAFs and > garbage collecting. > > Here is the profiling report from my original version w/o StateT > http://lpaste.net/108995 > > Slow version with StateT > http://lpaste.net/108997 > > Here is the "makeBucket" function that is referenced (it is the same in > both state and nonstate): > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > Looking at stacked overflow and the official docs I have gotten an idea of > what is going on. The heaps generated between them tells me that a lot more > memory is being allocated to lists. These heaps were generated running my > render function against a template with nested loops and a list of elements. > > http://imgur.com/a/2jOIf > > I am hoping that maybe someone could give me a hint at what to look at > next. I've played around with Strictness and refactoring loops to no avail > and now am kind of stuck. Any help would be appreciated. > > -- > Kyle Hanson > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/b4c26366…> ------------------------------ Message: 8 Date: Fri, 8 Aug 2014 11:24:29 +0800 From: jun zhang <zhangjun.julian(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] How to improve the zipwith's performance Message-ID: <CAGjcJLcT0FAmNxFLbdaZZfMFg5aEL1rZDPEWOpRxvsKJsau3ew(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Dear All I write a code for Clustering with Data.Clustering.Hierarchical, but it's slow. I use the profiling and change some code, but I don't know why zipwith take so many time? (even I change list to vector) My code is as blow, Any one kindly give me some advices. ====================== main = do .... let cluster = dendrogram SingleLinkage vectorList getVectorDistance .... getExp2 v1 v2 = d*d where d = v1 - v2 getExp v1 v2 | v1 == v2 = 0 | otherwise = getExp2 v1 v2 tfoldl d = DV.foldl1' (+) d changeDataType:: Int -> Double changeDataType d = fromIntegral d getVectorDistance::(a,DV.Vector Int)->(a, DV.Vector Int )->Double getVectorDistance v1 v2 = fromIntegral $ tfoldl dat where l1 = snd v1 l2 = snd v2 dat = DV.zipWith getExp l1 l2 ======================================= build with ghc -prof -fprof-auto -rtsopts -O2 log_cluster.hs run with log_cluster.exe +RTS -p profiling result is log_cluster.exe +RTS -p -RTS total time = 8.43 secs (8433 ticks @ 1000 us, 1 processor) total alloc = 1,614,252,224 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc getVectorDistance.dat Main 49.4 37.8 tfoldl Main 5.7 0.0 getExp Main 4.5 0.0 getExp2 Main 0.5 1.5 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140808/d29aa298…> ------------------------------ Message: 9 Date: Fri, 08 Aug 2014 06:31:49 +0200 From: Bardur Arantsson <spam(a)scientician.net> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <ls1jrl$7gp$1(a)ger.gmane.org> Content-Type: text/plain; charset=utf-8 On 2014-08-07 19:57, Kyle Hanson wrote: > Hello, > > Here is the "makeBucket" function that is referenced (it is the same in > both state and nonstate): > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > Just a shot in the dark, but I notice that you're using "modify" and not "modify'" which was added in a recent version of transformers. Strict.StateT is not always "strict enough" and you may need to use modify'. At any rate, it's worth a shot, I think. Regards, ------------------------------ Message: 10 Date: Thu, 7 Aug 2014 22:30:25 -0700 From: Jan Paul Posma <me(a)janpaulposma.nl> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Visualising Haskell function execution Message-ID: <CAPtY9n+6onYBYb=pWP4NRmLq43zY6MGXQMuhmp2HfnUzhuOiyA(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hey all, Last weekend my friend Steve and I did a small project for visualising Haskell function execution in the browser. It's meant to be used in education, and uses a tiny custom parser. I figured it could be of interest for anyone here learning or teaching Haskell: https://stevekrouse.github.io/hs.js/ To see it in action, scroll a bit down to the red bordered box, and click on "map", and then keep clicking on each new line. I hope it can be useful to someone. Cheers, JP -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/3c4dabe9…> ------------------------------ Message: 11 Date: Thu, 7 Aug 2014 23:56:43 -0700 From: John Lato <jwlato(a)gmail.com> To: Bardur Arantsson <spam(a)scientician.net> Cc: haskell-cafe <haskell-cafe(a)haskell.org> Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAJ727GipLL12TXfrMBeLJBX2_GdoD0W-CKJd4U1cu48CvnkrBg(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" On Thu, Aug 7, 2014 at 9:31 PM, Bardur Arantsson <spam(a)scientician.net> wrote: > On 2014-08-07 19:57, Kyle Hanson wrote: > > Hello, > > > > Here is the "makeBucket" function that is referenced (it is the same in > > both state and nonstate): > > > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > > > Just a shot in the dark, but I notice that you're using "modify" and not > "modify'" which was added in a recent version of transformers. > > Strict.StateT is not always "strict enough" and you may need to use > modify'. > > At any rate, it's worth a shot, I think. > Good point. I think that even modify' will not be strict enough without adding strictness to RenderState as well. John L. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/ce617687…> ------------------------------ Subject: Digest Footer _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ End of Haskell-Cafe Digest, Vol 132, Issue 11 *********************************************

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Performance of StateT and best practices for debugging
by Kyle Hanson 08 Aug '14

08 Aug '14

Hello, I was looking at cleaning up my refactoring a core loop of template rendering to go from a loop with many parameters loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] -> ExceptT StrapError m Builder to a looped state monad transformer loop :: [Pieces] -> RenderT m Builder newtype RenderT m a = RenderT { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a } deriving ( Functor, Applicative, Monad, MonadIO ) data RenderState m = RenderState { position :: SourcePos , renderConfig :: RenderConfig , blocks :: BlockMap , bucket :: InputBucket m } however, there is a big slow down (about 6-10x) using a StateT. I think it might have something to do with laziness but I am not exactly sure of where to begin in tracking it down. Swapping out the Lazy State to a Strict State helps a little (only a 5x slow down) You can find some of the processing code here: https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… With my old loop commented out. Its messy right now since I am just trying a number of different approaches. I did some more work factoring out the lifts, trying different iterations of foldlM and stuff but that didn't have that much of an effect on performance. After profiling I see in the StateT, the report has a lot more CAFs and garbage collecting. Here is the profiling report from my original version w/o StateT http://lpaste.net/108995 Slow version with StateT http://lpaste.net/108997 Here is the "makeBucket" function that is referenced (it is the same in both state and nonstate): https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… Looking at stacked overflow and the official docs I have gotten an idea of what is going on. The heaps generated between them tells me that a lot more memory is being allocated to lists. These heaps were generated running my render function against a template with nested loops and a list of elements. http://imgur.com/a/2jOIf I am hoping that maybe someone could give me a hint at what to look at next. I've played around with Strictness and refactoring loops to no avail and now am kind of stuck. Any help would be appreciated. -- Kyle Hanson

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[ANN] rtorrent-state 0.1.0.0
by Mateusz Kowalczyk 07 Aug '14

07 Aug '14

Hi, rtorrent-state is a library that allows working with rtorrent state files (SOMEHASH.torrent.rtorrent) placed in your session directory. If you're an rtorrent user and ever had to manually muck around with those files, you should be able to use this library to make your life easier. For example, you can stop all torrents in your session directory with just: “overFilesIn "rtorrent/session/dir" stopTorrent” The way it works is by parsing the session files, modifying the resulting data type and serialising it back into the file. I did not do optimisation but I had no problem with test sample of 100,000 files. I need to add IOException handling and maybe extra utility functions but otherwise I consider the library finished. Thanks -- Mateusz K.

1 0

parsec: problem combining lookAhead with many1 (bug?)
by silly8888 07 Aug '14

07 Aug '14

Suppose that we have the following parser: p = lookAhead (char 'a') >> char 'b' If we use it like so parse p "" "a" we get the following error: Left (line 1, column 1): unexpected "a" expecting "b" What happened is that char 'a' succeeded by consuming the 'a' from the input and then lookAhead rewinded the input stream (as it does on success). Then, char 'b' tries to parse (again) the first character of the input and fails. Everything works as expected. Now let's slightly modify our parser: p' = lookAhead (many1 $ char 'a') >> char 'b' I've only added a many1. I was expecting this parser to give the same error as the previous one: many1 $ char 'a' will succeed consuming one 'a' and then lookAhead will rewind the input (as it does on success). Thus when we call char 'b' we are going to be in the beginning of the input again. Well, that doesn't happen: Left (line 1, column 2): unexpected end of input expecting "b" As you can see, lookAhead did not rewind the input as it was supposed to.

2 1

Side-by-side pretty printing
by Michael Lazarev 07 Aug '14

07 Aug '14

Hi all, When looking into Text.PrettyPrint, I stumbled upon <> (beside) combinator. Is it true that multi-line documents can't be printed one beside other? E.g. this let doc1 = vcat $ map text ["This", "is", "a", "document"] in doc1 <> doc1 prints this: This is a documentThis is a document As well as if I would write `doc1 <> nest 50 doc1`. What I was expecting, was This This is is a a documentdocument Do I get it right that Text.PrettyPrint was not intended for such things?

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Haskell Weekly News: Issue 301
by Daniel Santa Cruz 07 Aug '14

07 Aug '14

Welcome to issue 301 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from July 27 to August 2, 2014 Quotes of the Week * bernalex: I used to have a problem then I used lens now I have an abstraction problem? * trap_exit: haskell is like the 'and they lived happily ever after' of programming languages Top Reddit Stories * The Comonad.Reader » Letter to a Young Haskell Enthusiast Domain: comonad.com, Score: 236, Comments: 56 Original: [1] http://goo.gl/Z5usp3 On Reddit: [2] http://goo.gl/CpPKnC * seL4 is now open source: the world's first end-to-end verified OS kernel Domain: github.com, Score: 87, Comments: 20 Original: [3] http://goo.gl/Uz50bj On Reddit: [4] http://goo.gl/EQK0MQ * FP Haskell Center now free for open projects Domain: fpcomplete.com, Score: 81, Comments: 23 Original: [5] http://goo.gl/ULc9ze On Reddit: [6] http://goo.gl/ZleWCk * -XOverlappingInstances and -XIncoherentInstances to be deprecated Domain: haskell.org, Score: 76, Comments: 64 Original: [7] http://goo.gl/dokkrY On Reddit: [8] http://goo.gl/0AyqA2 * First-Class "Statements": IO as data Domain: blog.jle.im, Score: 68, Comments: 32 Original: [9] http://goo.gl/JNj2D1 On Reddit: [10] http://goo.gl/h1v7yp * Foldable and Traversable in Haskell Domain: blog.jakubarnold.cz, Score: 61, Comments: 30 Original: [11] http://goo.gl/mgI6Mg On Reddit: [12] http://goo.gl/nvwj6j * Minimalist GUI toolkit in GHCi Domain: github.com, Score: 61, Comments: 7 Original: [13] http://goo.gl/9PvsUP On Reddit: [14] http://goo.gl/jQKyG7 * early adopters rejoyce! Haskell Platform 2014.2.0.0 Release Candidate 2 Domain: haskell.org, Score: 48, Comments: 27 Original: [15] http://goo.gl/AGl5po On Reddit: [16] http://goo.gl/ThS3Wc * The Modular, Functional Client Side Domain: stackbuilders.com, Score: 46, Comments: 3 Original: [17] http://goo.gl/eydkfz On Reddit: [18] http://goo.gl/z9q8hE * Beware of bracket Domain: ro-che.info, Score: 46, Comments: 18 Original: [19] http://goo.gl/UYA2mF On Reddit: [20] http://goo.gl/ksMQVV * Real World Haskell: Shipping "Carnival", a Blog Commenting Service Domain: robots.thoughtbot.com, Score: 44, Comments: 5 Original: [21] http://goo.gl/UmPyiL On Reddit: [22] http://goo.gl/4PRdpm * Flee traveller! Flee or you will be corrupted and devoured! Domain: github.com, Score: 41, Comments: 16 Original: [23] http://goo.gl/e3sA6X On Reddit: [24] http://goo.gl/RuAZ4o * Reading files from the /proc filesystem Domain: yesodweb.com, Score: 35, Comments: 4 Original: [25] http://goo.gl/mVfVyM On Reddit: [26] http://goo.gl/Bd2HBT * clckwrks CMS source now on github. A sad farewell to darcs and an optimistic look towards greater contributions from the community. Domain: clckwrks.com, Score: 33, Comments: 31 Original: [27] http://goo.gl/ZLqVWl On Reddit: [28] http://goo.gl/q0za2l * Introduction to GHC.TypeLits with base 4.7, including runtime conversion of symbols. Domain: ponies.io, Score: 32, Comments: 13 Original: [29] http://goo.gl/6FtdyO On Reddit: [30] http://goo.gl/PpmkOc * Converting Make to Shake Domain: neilmitchell.blogspot.com, Score: 23, Comments: 14 Original: [31] http://goo.gl/dOWVhV On Reddit: [32] http://goo.gl/cHYTmS * Learn Snap: Interactive Snap + Heist Examples Domain: learnsnap.chromaticleaves.com, Score: 21, Comments: 14 Original: [33] http://goo.gl/Opwt40 On Reddit: [34] http://goo.gl/06AneL * Hackage: ghc-server: A server interface to GHC. Domain: hackage.haskell.org, Score: 18, Comments: 14 Original: [35] http://goo.gl/ZjhScl On Reddit: [36] http://goo.gl/b9wBfP * Bloggy Badger: Homemade FRP: a study in following the types Domain: gelisam.blogspot.com, Score: 17, Comments: 1 Original: [37] http://goo.gl/T7ujN3 On Reddit: [38] http://goo.gl/HAV1mR Top StackOverflow Questions * IO/Monadic assign operator causing ghci to explode for infinite list votes: 16, answers: 1 Read on SO: [39] http://goo.gl/TC0Snn * A performance conundrum votes: 14, answers: 1 Read on SO: [40] http://goo.gl/b910ez * Does an unused let binding have any effect in Haskell? votes: 12, answers: 3 Read on SO: [41] http://goo.gl/KEl13j * In Haskell, are guards or matchers preferable? votes: 12, answers: 1 Read on SO: [42] http://goo.gl/LiXDjk * If MonadPlus is the “generator” class, then what is the “consumer” class? votes: 12, answers: 2 Read on SO: [43] http://goo.gl/eqRu3a * Why would using head/tail instead of pattern matching make evaluation terminate? votes: 12, answers: 3 Read on SO: [44] http://goo.gl/LOjX0V Until next time, [45]+Daniel Santa Cruz References 1. http://comonad.com/reader/2014/letter-to-a-young-haskell-enthusiast/ 2. http://www.reddit.com/r/haskell/comments/2cbbgf/the_comonadreader_letter_to… 3. https://github.com/seL4/seL4 4. http://www.reddit.com/r/haskell/comments/2c1bnp/sel4_is_now_open_source_the… 5. https://www.fpcomplete.com/business/blog/fp-haskell-center-going-free/ 6. http://www.reddit.com/r/haskell/comments/2c9u0g/fp_haskell_center_now_free_… 7. http://www.haskell.org/pipermail/ghc-devs/2014-July/005830.html 8. http://www.reddit.com/r/haskell/comments/2c136i/xoverlappinginstances_and_x… 9. http://blog.jle.im/entry/first-class-statements 10. http://www.reddit.com/r/haskell/comments/2byuhj/firstclass_statements_io_as… 11. http://blog.jakubarnold.cz/2014/07/30/foldable-and-traversable.html 12. http://www.reddit.com/r/haskell/comments/2c8b87/foldable_and_traversable_in… 13. https://github.com/divipp/lensref/wiki 14. http://www.reddit.com/r/haskell/comments/2cge6f/minimalist_gui_toolkit_in_g… 15. http://www.haskell.org/pipermail/haskell/2014-July/024276.html 16. http://www.reddit.com/r/haskell/comments/2c0ep4/early_adopters_rejoyce_hask… 17. http://www.stackbuilders.com/news/the-modular-functional-client-side 18. http://www.reddit.com/r/haskell/comments/2c21j0/the_modular_functional_clie… 19. http://ro-che.info/articles/2014-07-30-bracket.html 20. http://www.reddit.com/r/haskell/comments/2c4li4/beware_of_bracket/ 21. http://robots.thoughtbot.com/ship-you-a-haskell 22. http://www.reddit.com/r/haskell/comments/2cfdms/real_world_haskell_shipping… 23. https://github.com/haskell/bytestring/blob/2530b1c28f15d0f320a84701bf507d56… 24. http://www.reddit.com/r/haskell/comments/2cbgpz/flee_traveller_flee_or_you_… 25. http://www.yesodweb.com/blog/2014/07/reading-files-proc-filesystem 26. http://www.reddit.com/r/haskell/comments/2buufk/reading_files_from_the_proc… 27. http://www.clckwrks.com/page/view-page-slug/12/clckwrks-now-on-github 28. http://www.reddit.com/r/haskell/comments/2cd26w/clckwrks_cms_source_now_on_… 29. http://ponies.io/posts/2014-07-30-typelits.html 30. http://www.reddit.com/r/haskell/comments/2c8bfi/introduction_to_ghctypelits… 31. http://neilmitchell.blogspot.com/2014/07/converting-make-to-shake.html 32. http://www.reddit.com/r/haskell/comments/2bukaj/converting_make_to_shake/ 33. http://learnsnap.chromaticleaves.com/ 34. http://www.reddit.com/r/haskell/comments/2cdc36/learn_snap_interactive_snap… 35. http://hackage.haskell.org/package/ghc-server-1.0 36. http://www.reddit.com/r/haskell/comments/2c17zz/hackage_ghcserver_a_server_… 37. http://gelisam.blogspot.com/2014/07/homemade-frp-study-in-following-types.h… 38. http://www.reddit.com/r/haskell/comments/2c0vg4/bloggy_badger_homemade_frp_… 39. http://stackoverflow.com/questions/24986296/io-monadic-assign-operator-caus… 40. http://stackoverflow.com/questions/25089668/a-performance-conundrum 41. http://stackoverflow.com/questions/24984661/does-an-unused-let-binding-have… 42. http://stackoverflow.com/questions/25000929/in-haskell-are-guards-or-matche… 43. http://stackoverflow.com/questions/25070740/if-monadplus-is-the-generator-c… 44. http://stackoverflow.com/questions/25078598/why-would-using-head-tail-inste… 45. https://plus.google.com/105107667630152149014/about

1 0

Dealing with encodings
by Dmitry Bogatov 06 Aug '14

06 Aug '14

Hello! How teach hxt to handle "KOI8-R" encoding of input file? And it seems that so many great packages (like hxt, feed, curl) uses String. Is it some work in progress to port them to Text? -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter, esperantisto and netiquette guardian. GPG: 54B7F00D

5 7

Applicative & Monad as interaction between categories
by Ruben Astudillo 05 Aug '14

05 Aug '14

Hi all, I recently came across of two blog posts[1][2] by Gabriel Gonzales where he shows motivation for writing compositional functions -- and thus why the concept of category is useful -- and motivation to write functors between them. I wanted to know if something similar for has been done to `Applicative' and `Monad' as design pattern and interaction between categories. I've searching but I always hit the Monad tutorials and more info on how to use them. Thanks in advance. Excuse my English. [1]: http://www.haskellforall.com/2012/08/the-category-design-pattern.html [2]: http://www.haskellforall.com/2012/09/the-functor-design-pattern.html -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

3 2

[ANN] Hayoo Relaunch
by Sebastian Philipp 05 Aug '14

05 Aug '14

Hi Cafe, Hayoo <http://hayoo.fh-wedel.de> has been relaunched. Hayoo is a search engine for Hackage packages, which allows you to search for functions, data types and packages. It is currently work in progress. Any feedback is greatly appreciated! Hayoo uses Hunt <https://github.com/hunt-framework> for indexing and searching, which is the successor of Holumbus. Hunt is a flexible, lightweight search platform with a powerful query language and JSON API. Example search requests are: * Function names: map <http://hayoo.fh-wedel.de/?query=map> * Function signatures: (a->b)->f a->f b <http://hayoo.fh-wedel.de/?query=%28a-%3Eb%29-%3Ef+a-%3Ef+b> * Module names: Control.Loop <http://hayoo.fh-wedel.de/?query=Control.Loop> Have a look at the examples on <http://hayoo.fh-wedel.de/examples> for some advances queries. The old Hayoo and Holumbus are still online at <http://holumbus-alt.fh-wedel.de/> -- Sebastian Philipp

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Fwd: Default stdout buffering of child process of createProcess
by Chris Myzie 05 Aug '14

05 Aug '14

I'm reposting this message because I think it only went to the google group and not the official haskell-cafe list: On Friday, August 1, 2014 10:06:32 AM UTC-4, Chris Myzie wrote: > > As a workaround, I am able to trick the child haskell process into > thinking it's running in an interactive terminal by wrapping it with > /usr/bin/script: > > createProcess (proc "/usr/bin/script" ["-qc","./A","/dev/null"]) { std_out > = CreatePipe } > > I still think haskell is using screwy defaults for stdout buffering.. > > On Thursday, July 31, 2014 3:24:47 PM UTC-4, Chris Myzie wrote: >> >> Hello, >> >> I'm trying to write a wrapper process that will be able to read any child >> process' stdout. The problem I'm running into is that unless I force the >> child's stdout to LineBuffering, it defaults to BlockBuffering. Is >> BlockBuffering really the default in this case? I don't want to have to >> modify all of the child processes that I want to use with this wrapper. >> >> Below is a simple test case. A.hs is the child process, and B.hs is the >> wrapper. If I run B.hs, I will get no output unless I uncomment the line >> in A.hs. >> >> Thanks, >> Chris >> >> >> ------------------------------ A.hs --------------------------- >> import Control.Concurrent >> import System.IO >> >> main :: IO () >> main = do >> -- hSetBuffering stdout LineBuffering >> putStrLn "test" >> threadDelay 1000000 >> main >> >> >> ------------------------------ B.hs --------------------------- >> import Control.Monad >> import System.IO >> import System.Process >> >> main :: IO () >> main = do >> (_,Just h,_,_) <- createProcess (proc "./A" []) { std_out = CreatePipe } >> hSetBuffering h LineBuffering >> forever $ hGetLine h >>= putStrLn >> >

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[ANN] StrappedTemplates - general purpose templates
by Kyle Hanson 04 Aug '14

04 Aug '14

Hello all, I found that I wasn't quite satisfied by the template offerings (Heist, Hastache, Shakespearean, etc..) of Haskell, so I built my own. The goal is to have simple syntax that non-haskellers would be comfortable using, resembles templates found in other languages (Jinja, Django, etc) and an interface to render them that I don't have to think very hard to use. Features include inheritance, logic, includes, functions, and relatively speedy rendering (much faster than interpreted templates like Heist-I and Hastache) . Its very much a work in progress, but I felt that it was enough for an initial release and get general feedback on it. Comments are appreciated. One thing that I want to improve is how functions are handled in the template and in the "InputBucket", extend the syntax to allow you to do more inside the template and be able to define your own block functions. These will probably be added next major release. http://hackage.haskell.org/package/StrappedTemplates https://github.com/hansonkd/StrappedTemplates Thanks! Kyle Hanson

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New Functional Programming Job Opportunities
by Functional Jobs 04 Aug '14

04 Aug '14

Here are some functional programming job opportunities that were posted recently: Pragmatic Haskell Developer at Anchor Systems http://functionaljobs.com/jobs/8729-pragmatic-haskell-developer-at-anchor-s… Cheers, Sean Murphy FunctionalJobs.com

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