- Haskell-Cafe - Haskell.org

DNS problems at haskell.org?
by Eugene Kirpichov 18 Dec '10

18 Dec '10

Hello. For a couple of friends of mine, hackage.haskell.org happens to resolve to something strange (parked domain), though haskell.org works ok. This might be something to tell to haskell.org admins. Find below an example tracert (messages in Russian have been translated). C:\Program Files (x86)\Far2>tracert hackage.haskell.org Tracing to hackage.haskell.org [209.62.105.19], max hops = 30 1 8 ms 4 ms 4 ms bsr01.nn.ertelecom.ru [91.144.184.69] 2 * * 2 ms net184-77.nn.ertelecom.ru [91.144.184.77] 3 13 ms 9 ms 9 ms NNOV-D2-HQ-XX---1-3-0.499.main.synterra.ru [83.229.187.17] 4 9 ms 29 ms 9 ms 83.229.226.101 5 10 ms 9 ms 9 ms m9-cr01-te4-3.msk.stream-internet.net [195.34.38.37] 6 142 ms 142 ms 142 ms ss-crs-1-be3.msk.stream-internet.net [195.34.53.86] 7 142 ms 142 ms 142 ms mar-crs-1-be6.msk.stream-internet.net [195.34.59.141] 8 143 ms 142 ms 142 ms oct-crs-1-be1.spb.stream-internet.net [195.34.53.194] 9 143 ms 142 ms 142 ms bro-cr01-be3.stk.stream-internet.net [212.188.1.194] 10 66 ms 66 ms 66 ms tct-cr01-te5-1.ams.stream-internet.net [195.34.53.14] 11 142 ms 307 ms 207 ms sd-cr01-te2-1.nyc.stream-internet.net [195.34.59.114] 12 * * * Request timed out 13 179 ms 179 ms 179 ms e8-2.ibr03.dllstx3.networklayer.com [70.87.253.189] 14 190 ms 189 ms 190 ms e1-1.ibr01.hstntx2.networklayer.com [70.87.253.50] 15 190 ms 190 ms 190 ms te2-2.dsr02.hstntx2.networklayer.com [74.55.252.38] 16 184 ms 185 ms 184 ms po2.car3.hstntx2.networklayer.com [74.55.252.106] 17 189 ms 189 ms 189 ms ev1s-209-62-105-19.theplanet.com [209.62.105.19] Trace finished C:\Program Files (x86)\Far2>tracert haskell.org Tracing to haskell.org [78.46.100.180], max hops = 30 1 4 ms 3 ms 2 ms bsr01.nn.ertelecom.ru [91.144.184.69] 2 * 2 ms 2 ms net184-77.nn.ertelecom.ru [91.144.184.77] 3 10 ms 9 ms 9 ms NNOV-D2-HQ-XX---1-3-0.499.main.synterra.ru [83.229.187.17] 4 9 ms 9 ms 11 ms 83.229.226.101 5 10 ms 9 ms 9 ms m9-cr01-te4-3.msk.stream-internet.net [195.34.38.37] 6 55 ms 55 ms 55 ms ss-crs-1-be3.msk.stream-internet.net [195.34.53.86] 7 53 ms 52 ms 52 ms m9-crs-1-be9.msk.stream-internet.net [195.34.59.250] 8 55 ms 55 ms 55 ms bor-crs-1-be1.spb.stream-internet.net [195.34.53.126] 9 52 ms 52 ms 52 ms anc-cr01-po3.ff.stream-internet.net [195.34.53.102] 10 52 ms 52 ms 52 ms anc-cr02-po1.ff.stream-internet.net [212.188.0.122] 11 56 ms 56 ms 56 ms decix2-gw.hetzner.de [80.81.193.164] 12 60 ms 60 ms 60 ms hos-bb1.juniper1.fs.hetzner.de [213.239.240.242] 13 64 ms 61 ms 63 ms hos-tr1.ex3k10.rz12.hetzner.de [213.239.228.139] 14 60 ms 60 ms 62 ms lambda.haskell.org [78.46.100.180] Trace finished -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

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Making type-incompatible strategies interchangeable
by Jacek Generowicz 18 Dec '10

18 Dec '10

# Imagine an activity which may be performed either by a computer, or # by a human (alternatively, either locally, or remotely across a # network). From Haskell's type system's perspective, these two will # look completely different (most obviously, the human (or the # network) is wrapped in IO). How can they be made interchangeable ? # To demonstrate what I mean, I offer the following concrete toy # example, in Python. # It's a harness for playing the trivial higher-lower number guessing # game, with interchangeable strategies for either player. In this # example I provide two strategies (Computer / ask Human via IO) for # each role (asker and guesser). # How can this sort of interchangeability of computations which are # conceptually identical, but incompatible from the types perspective, # be expressed in Haskell? from random import randint # A simple game harness. It is given the two players, and mediates the # interaction between them. def game(asker, guesser): feedback = None count = 0 while not feedback == 0: guess = guesser(feedback) feedback = asker(guess) print "Guess: %s, Answer: %s" % (guess, feedback) count += 1 print "Got it in", count # A couple of decorators to smoothe the use of the generators which # are used to implement the players. def hide_send(generator_function): def proxy(*args, **kwds): return generator_function(*args, **kwds).send return proxy def advance(hidden_send_proxy): def proxy(*args, **kwds): send = hidden_send_proxy(*args, **kwds) send(None) return send return proxy # Artificial player who knows the secret @advance @hide_send def higher_lower_asker_C(low=0, high=100): secret = randint(low, high) guess = yield while True: guess = yield cmp(guess, secret) # Artificial player trying to guess the secret @hide_send def higher_lower_guesser_C(low=0, high=100): while True: guess = (low + high) // 2 feedback = yield guess if feedback < 0: low = guess else: high = guess # Interface to human who knows the secret @advance @hide_send def higher_lower_asker_H(): guess = yield # No feedback before first guess while True: print "My guess is", guess print "Please reply with one letter: is my guess (l)ow, (c)orrect or (h)igh ?" guess = yield {'l':-1, 'c':0, 'h':1 }[raw_input()] # Interface to human trying to guess @hide_send def higher_lower_guesser_H(): while True: feedback = yield input("What is your guess? ") print {-1:"Too low.", 0:"Correct!", +1:"Too high."}[feedback] # Given the above preparation, the game can now be played in all 4 # possible permutations of Computer/Human vs. Computer/Human. game(higher_lower_asker_C(), higher_lower_guesser_C()) game(higher_lower_asker_H(), higher_lower_guesser_C()) game(higher_lower_asker_C(), higher_lower_guesser_H()) game(higher_lower_asker_H(), higher_lower_guesser_H())

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Re: [Haskell-cafe] Infinite lists in real world programs
by Yves Parès 18 Dec '10

18 Dec '10

Thanks you all for your links, I will read this. However, Brent, I fail to understand your implementation of Monad... I understand the purpose, but not the algorithm. 2010/12/18 Matthew Sottile <mjsottile(a)mac.com> > Hi- > > This may be of some interest: > > https://github.com/mjsottile/hsworkflow/raw/master/docs/works09paper.pdf > > That describes a simple project that I think is similar to what you are > looking at doing. The code is in that github repository as well, a couple > directories up from the paper. > > https://github.com/mjsottile/hsworkflow/ > > -m > > > On Dec 15, 2010, at 5:52 AM, Yves Parès wrote: > > > Hello Café, > > > > I was wondering if using infinite lists was a viable and efficient > solution in haskell programs (I mean not simple prototypes) : > > I was considering using them to model agents in a hierarchical > multi-agent application for school. > > A list would representate the state of an agent at a step of the program. > > > > Let's say we have two simple agents, one multiplying its input by 2 and > the other dividing it by 4 : > > > > > > agent1 = fmap (*2) > > agent2 = fmap (/4) > > > > allValues = xs where > > ys = agent1 xs > > xs = 100:agen2 ys > > > > main = do > > mapM_ print $ take 100 allValues > > > > > > Of course, in a real program, an agent would rather take a list of > multiple agents (i.e. a list of lists) in input, so that its ouput could > depend on what several agents feed him. > > > > Some could state what I'm trying to do is FRP, and I agree. But it > remains a simple goal so I'd like to keep the program simple, and not go > into the whole complexity of a FRP framework (and I'm working with a > non-haskeller). > > For instance, with my solution, I cannot dynamically connect or > disconnect agents during the runtime, but I'll will not need to do that in > my program. > > Besides, I'd like to try to implement this myself, not use an already > existing framework. > > > > So is it viable or would the use of multiple infinite lists kill the > performances? > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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ByteString or Text version of getDirectoryContents
by Jesse Schalken 18 Dec '10

18 Dec '10

Is there a ByteString or Text version of getDirectoryContents? I am writing a program which scans a filesystem and it runs out of memory using Strings for all the file names, and I would like to avoid the overhead of calling ByteString.pack on the results of getDirectoryContents. I don't mind if it only works on POSIX, but System.Posix.Directory.readDirStream returns a String as well, and looking at how readDirStream is implemented I am left puzzled as it looks like it is using calls to native C functions but I can't find where the C string is turned into a String so I can change it to a ByteString or Text. Thanks, Jesse

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Looking for Haskell job at China.
by Andy Stewart 18 Dec '10

18 Dec '10

Hi all, I'm a Chinese haskeller, i'm looking for haskell job at *China*. Please contact me if any Chinese company interested me. Below is my skills: * Java : (2007-06 ~ 2008-09) Worked on a variety of commercial J2ME games, masterpiece <<Machine King>> : http://goo.gl/lcJF * Elisp : (2008-07 ~ 2009-05) Emacs expert, developed over a large number of Emacs extensions : http://goo.gl/DNLj My best-known Emacs extensions are: AutoInstall (automatic installation of Emacs extensions): http://goo.gl/ogBY MultiTerm (terminal emulator): http://goo.gl/PwpO Yaoddmuse (OddmuseWiki editor): http://goo.gl/cUrA ElispFormat (Elisp formatter): http://goo.gl/nVzb Irfc (RFC document reader): http://goo.gl/XZwi ... too much :) Other emacs extensions and elisp code, please see my EmacsWiki homepage: http://goo.gl/DNLj * Haskell : (2009-05 ~ 2010) Haskell/Gtk+ expert. Developer of gtk2hs (Haskell binding to GTK+) : http://goo.gl/AhJw Development of a large number of Haskell libraries: http://goo.gl/CoV0 I'm developing my own Haskell operating system : Video: http://www.youtube.com/watch?v=weS6zys3U8k Homepage: http://hackage.haskell.org/package/manatee Screenshots: http://goo.gl/MkVw Framework: http://goo.gl/otfb http://goo.gl/DMFW Source Repository: http://goo.gl/CoV0 I have finish below modules in my Haskell OS: Webkit-Browser: http://goo.gl/uoaX Editor: http://goo.gl/ouDR File Manager: http://goo.gl/x8Xi Picture Viewer: http://goo.gl/EYih PDF reader: http://goo.gl/8jCK Process Manager: http://goo.gl/ISOr Music Player: http://goo.gl/TMeD IRC client: http://goo.gl/kY6v News reader: http://goo.gl/BYVp Download-Manager: http://goo.gl/30tTN Terminal-Emulator: http://goo.gl/VMyaN Below are modules in developing: Mail-Client, IDE framework.... Thanks, -- Andy

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Layout styles and EclipseFP evolution.
by Scott Michel 18 Dec '10

18 Dec '10

Disclaimer: I'm not looking to start a favorite IDE flame war, or resurrect Emacs vs. VIM vs. Yi vs. <insert your favorite IDE here> discussions. I've been helping JP with EclipseFP, with the objective of evolving EclipseFP into a relatively high productivity IDE for Haskell. EclipseFP has the potential to mature into a reasonable platform for making routine coding easy, e.g., a HAppStack plugin that makes writing web apps in Haskell just as easy as it is for the Java community to write web services. I've just added Haskell code templates (*) to EclipseFP and, in the process, encountered the distinct lack of layout autoindentation. I'm sure it used to exist, but it doesn't exist today. I've looked at the Emacs haskell-mode.el indentation style, which I'm inclined to port over. Are there other layout autoindentation styles that other people prefer and believe should be supported? -scooter (*) The current development version supports templates like "let<Ctrl+Space>" and you get a let expression inserted. Eventually, if you were to type "case<Ctrl+Space>" and you tab out of the expression between "case" and "of", you would get the data type's alternatives inserted. (**) Don S told me that a similar "case" autocompletion exists in another IDE. Yes, EclipseFP is just catching up. (***) Wishlist: An incremental parser that can accept document changes/deltas and can look backward from the current point to give better context for completions, e.g., the previous token before the editor's point is "import".

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OT: Monad co-tutorial: the Compilation Monad
by Gregg Reynolds 17 Dec '10

17 Dec '10

This is a little off-topic, since it isn't specifically about Haskell, but since Haskell is the home of the monad tutorial it isn't completely irrelevant. The monad tutorial genre is well-known; it's often written somebody who has just learned the concept trying to explain it, often in highly imaginative terms (e.g. "a monad is just like a giant squid, with special tentacles"). I propose "monad co-tutorial" for attempts, often by an amateur (e.g. me) to work out how a monad appears in an unexpected place. In particular, I recently suffered through a few days of learning to deal with Ant and Maven2, which got me thinking about build systems in general, which got me thinking about the (meta-)language used in such systems, which got me thinking about What It's Really All About. Lo and behold - a monad! I think, anyway. The basic idea is that program texts (source or object code) are to programs as sentences are to propositions. Compilation transforms one representation into another. This can be viewed in terms of the unit natural transformation of a monad of transformations over program representations. The multiplication component captures the fact that program text transformations can be chained, as in macro expansion, phased optimization, etc. I'm not sure if this works, but it fits my somewhat limited idea of monads, so I wrote an article <http://blog.mobileink.com/> about it and I'd appreciate any corrections. I expect if it does work somebody has already done something like it, so I would appreciate any pointers to more info. My real goal is to think about better language for software build systems, since what we have now is pretty weak, in my view. One thing that follows from thinking in terms of monads is that we can discard the notion of dependency of object code of source code in favor of a notion of equivalence (i.e. unit transform). My hunch is that thinking along such lines might lead to an improved metalanguage for build DSLs. Thanks, Gregg

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(Read r) => IO (Maybe r)
by Jacek Generowicz 17 Dec '10

17 Dec '10

Hi, What are some interesting, idiomatic ways of writing something similar to the following, using a) Only standard utilities b) Non-standard utilities getValidatedInteger = do maybeInt <- maybeGet case maybeInt of Just int -> return int Nothing -> do putStrLn "That doesn't seem to be an integer. Try again." getValidatedInteger maybeGet :: (Read r) => IO (Maybe r) maybeGet = getLine >>= return . maybeReadS maybeReadS text = case reads text of [(int, rest)] | all (== ' ') rest -> Just int _ -> Nothing

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bus error trying to use Network
by Marcelo Sousa 17 Dec '10

17 Dec '10

Hi, I'm getting a bus error with Network library on my Mac OS X 10.6.5. I have ghc 6.12.3, network 2.3. As an example: main = withSocketsDo $ do sock <- listenOn $ PortNumber 4244 (handle,host,port) <- accept sock hPutStr handle "Hi!" sClose sock Any idea of what the problem could be? If I use the Network.Socket library it works fine: main = withSocketsDo $ do sock <- socket AF_INET Stream 0 setSocketOption sock ReuseAddr 1 bindSocket sock (SockAddrInet 4244 iNADDR_ANY) listen sock 1 (csock,_) <- accept sock send csock "Hi!\n" sClose csock sClose sock Cheers, Marcelo

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What is NoPush module?
by Magicloud Magiclouds 17 Dec '10

17 Dec '10

Hi, When I compiling happstack with ghc 7, I got an error: src/Happstack/Server/Internal/Handler.hs:29:8: Could not find module `NoPush': Use -v to see a list of the files searched for. I looked around, there is no clue for the module NoPush, except it has a function call withNoPush. What is it? -- 竹密岂妨流水过山高哪阻野云飞

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syb-with-class problem.
by Magicloud Magiclouds 17 Dec '10

17 Dec '10

Hi, I am trying to make happstack work in my box, which is using ghc 7. While compiling HStringTemplate, which I did a little modification to make it work, I found that it does not work with template-haskell-2.5.0.0. I changed it to use template-haskell-2.4.0.1. This step worked fine. Then I got another error: $ cabal install Resolving dependencies... Configuring syb-with-class-0.6.1.1... Preprocessing library syb-with-class-0.6.1.1... Building syb-with-class-0.6.1.1... [1 of 4] Compiling Data.Generics.SYB.WithClass.Context ( Data/Generics/SYB/WithClass/Context.hs, dist/build/Data/Generics/SYB/WithClass/Context.o ) [2 of 4] Compiling Data.Generics.SYB.WithClass.Basics ( Data/Generics/SYB/WithClass/Basics.hs, dist/build/Data/Generics/SYB/WithClass/Basics.o ) [3 of 4] Compiling Data.Generics.SYB.WithClass.Derive ( Data/Generics/SYB/WithClass/Derive.hs, dist/build/Data/Generics/SYB/WithClass/Derive.o ) Data/Generics/SYB/WithClass/Derive.hs:23:1: Bad interface file: /home/magicloud/.cabal/lib/template-haskell-2.4.0.1/ghc-7.0.1/Language/Haskell/TH.hi Something is amiss; requested module template-haskell-2.4.0.1:Language.Haskell.TH differs from name found in the interface file template-haskell:Language.Haskell.TH cabal: Error: some packages failed to install: HStringTemplate-0.6.3 depends on syb-with-class-0.6.1.1 which failed to install. syb-with-class-0.6.1.1 failed during the building phase. The exception was: ExitFailure 1 How to resolve this? -- 竹密岂妨流水过山高哪阻野云飞

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Printing of asynchronous exceptions to stderr
by Mitar 17 Dec '10

17 Dec '10

Hi! I have been spend some time to debug this in my program. ;-) Why is ThreadKilled not displayed by RTS when send to thread (and unhandled), but any other exception is? For example, I am using custom exceptions to signal different kinds of thread killing. Based on those my threads cleanup in different ways. But after they cleanup they keep "running". Not really running as their computations were interrupted. But simply hanging there. And if then new custom exception arrives it is not handled anymore (as it is after my normal exception handlers already cleaned everything) and it is printed to stderr. Now I added "`finally` throwIO ThreadKilled" at the end of my cleanup computations to really kill the thread. So that possible later exceptions are not delivered anymore. Why it is not so that after all computations in a thread finish, thread is not killed/disposed of? Because it can be reused by some other computation? But then my exceptions could be delivered to wrong (new) thread while they were meant for old one? Mitar

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Re: [Haskell-cafe] [Haskell] Functor => Applicative => Monad
by Tillmann Rendel 17 Dec '10

17 Dec '10

Hi, John Smith wrote: > I would like to formally propose that Monad become a subclass of > Applicative A lot of code would break because of this change, but all problems should be reported at compile time, and are easy to fix. In most of the cases, either adding obvious Functor and Applicative instances to a library; or deleting such instances from a client, I would expect. This kind of clean-up would actually increase the quality of the library, however, and might therefore be acceptable. > The change is described on the wiki at > http://haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal There you write, among other things: > fail should be removed from Monad; a failed pattern match could error in the same way as is does for pure code. How is this part of the proposal related to Functor and Applicative? Since code depending on the current behavior can not be detected at compile time, this is a more serious change in a way: code keeps compiling but changes its meaning. Can you estimate how much code would break because of this change? Would it be possible to keep user-defined failure handling in do notation without keeping fail in Monad? Tillmann

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TLS package server interface do not seem to allow for asyncrhonious communication
by Mads Lindstrøm 17 Dec '10

17 Dec '10

Hi Haskeleers, I got a working SSL server using the TLS package. Great. However, I really intended to use SSL for an asynchronous server. That is, the server must constantly listen for a client message, which may result in zero or more messages send _to_ the client. And the server will, without being waken up by a client message, send messages to the client. And this interface http://hackage.haskell.org/packages/archive/tls/0.3.1/doc/html/Network-TLS-… do not seem to allow for an asynchronous server. That is, whenever I call: recvPacket :: Handle -> TLSServer IO (Either TLSError [Packet]) or recvData :: Handle -> TLSServer IO ByteString The server is stuck until the client sends a message. Or am I missing something? Contrast this to Network package socket implementation. Here I can spawn two threads and simultaneously listen for client messages and send messages to the client. It seems to me that a general SSL implementation should not preclude asynchronous servers. I know, the TLS package is not more than a few months old and one can already use it for SSL servers and clients, which is quite impressive. So do not read this as a negative comment, more as suggestions for a better interface. Regards, Mads Lindstrøm

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cpphs is missing from new Haskell.org server
by Dimitry Golubovsky 16 Dec '10

16 Dec '10

Hi, One more thing is missing after migration. The link found on the cpphs package page at Hackage, http://haskell.org/cpphs/ points to non-existing page. Thanks. -- Dimitry Golubovsky Anywhere on the Web

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Monadic Design Patterns for the Web C9 Video Series -- Part 2 is live!
by Greg Meredith 16 Dec '10

16 Dec '10

Dear Haskellians, Just in time for the Holidays! Best wishes, --greg ---------- Forwarded message ---------- From: Charles Torre <ctorre(a)microsoft.com> Date: Tue, Dec 14, 2010 at 11:31 AM Subject: Part 2 is live! To: Meredith Gregory <lgreg.meredith(a)gmail.com> Hi Greg! Part 2 is now live on 9. Front and center: http://channel9.msdn.com/Shows/Going+Deep/C9-Lectures-Greg-Meredith-Monadic… Thank you! See you in the new year to continue with this great series. Best, C -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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Infinite lists in real world programs
by Yves Parès 16 Dec '10

16 Dec '10

Hello Café, I was wondering if using infinite lists was a viable and efficient solution in haskell programs (I mean not simple prototypes) : I was considering using them to model agents in a hierarchical multi-agent application for school. A list would representate the state of an agent at a step of the program. Let's say we have two simple agents, one multiplying its input by 2 and the other dividing it by 4 : agent1 = fmap (*2) agent2 = fmap (/4) allValues = xs where ys = agent1 xs xs = 100:agen2 ys main = do mapM_ print $ take 100 allValues Of course, in a real program, an agent would rather take a list of multiple agents (i.e. a list of lists) in input, so that its ouput could depend on what several agents feed him. Some could state what I'm trying to do is FRP, and I agree. But it remains a simple goal so I'd like to keep the program simple, and not go into the whole complexity of a FRP framework (and I'm working with a non-haskeller). For instance, with my solution, I cannot dynamically connect or disconnect agents during the runtime, but I'll will not need to do that in my program. Besides, I'd like to try to implement this myself, not use an already existing framework. So is it viable or would the use of multiple infinite lists kill the performances?

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cannot install regex-posix using cabal ?
by z_axis 16 Dec '10

16 Dec '10

%ghc-pkg list|grep -i regex regex-base-0.93.2 %cabal install regex-posix Resolving dependencies... Configuring regex-posix-0.94.4... Preprocessing library regex-posix-0.94.4... running dist/build/Text/Regex/Posix/Wrap_hsc_make failed command was: dist/build/Text/Regex/Posix/Wrap_hsc_make >dist/build/Text/Regex/Posix/Wrap.hs cabal: Error: some packages failed to install: regex-posix-0.94.4 failed during the building phase. The exception was: ExitFailure 1 How can i fix such a problem ? ----- e^(π.i) + 1 = 0 -- View this message in context: http://haskell.1045720.n5.nabble.com/cannot-install-regex-posix-using-cabal… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] Iteratee-like
by John Lato 16 Dec '10

16 Dec '10

> > From: Permjacov Evgeniy <permeakra(a)gmail.com> > > current links > > https://github.com/permeakra/Rank2Iteratee > https://github.com/permeakra/PassiveIteratee > > The main difference from 'original' iteratees I read about is that both > do not use 'chunks' and pass data one-by-one. So, what I wrote may be > slower, but should be easier to maintain and more transparent for ghc > optimising facilities. I wanted as clean and simple code as possible, > but it is still very, very messy at some places and I want it cleaner. > Any suggestions? I also want to check, how good ghc does its work with > this messy modules. They may become interesting benchmarks. > Have you tried comparing it to either iteratee or enumerator (which had mostly comparable performance last time I checked, with a slight edge to iteratee)? Or to Oleg's library? Try writing test cases, a simple byte-counting application, or similar, so you can compare the performance with the other versions. Both enumerator and iteratee include demo programs that you could use as a starting point. I agree that iteratees which work on a per-element level are very clean and should be amenable to optimization by GHC. It also shows a very clear relationship with stream-fusion techniques. Unfortunately when I last tried it I couldn't get acceptable performance. I was using ghc-6.12.1 IIRC, so it could be different now. John

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Strong version of 'local' for reader monad
by Brent Yorgey 16 Dec '10

16 Dec '10

Hi all, Today I wanted this function strongLocal :: (MonadReader r1 m1, MonadReader r2 m2) => (r2 -> r1) -> m1 a -> m2 a Of course, after staring at this type for ten seconds I realized that it cannot be implemented. But I wondered whether anyone has any pointers to anything related, or if anyone has good ideas for a reasonable interface that would allow this. -Brent

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typesetting with lhs2tex
by Permjacov Evgeniy 16 Dec '10

16 Dec '10

I write docs for my iteratee-like library and I have problem with lhs2tex. When I execute lhs2tex and then latex, I get a document with long typesignatures and expressions expanded beyound page margins. I attached a sourcefile I have problem with. Can someone give me an advise how to force long signatures and expressions to be broken into multible lines ?

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ghc/dph
by Johannes Waldmann 16 Dec '10

16 Dec '10

Hi, I want to use dph (data parallel haskell) for a presentation. (Nothing fancy, just compile and run some demos.) What ghc version should I use and where do I get it? I read the advice "use HEAD" but when I build from the 7.1.20101213 source snapshot, dph is not installed (should it be?) Best - J.W.

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Re: [Haskell-cafe] Beginners help
by z_axis 16 Dec '10

16 Dec '10

According to map's definition, we know the 'fs' should be a list of function. so 'p' need a [a->b] as its parameter. And the result of 'p' should be a list of function which accepts [a] and return [b]. So the type of 'p' is [a->b] -> [[a] -> [b]] hope i make it clear. ----- e^(π.i) + 1 = 0 -- View this message in context: http://haskell.1045720.n5.nabble.com/Beginners-help-tp3306796p3307470.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 162 - December 15, 2010
by Daniel Santa Cruz 16 Dec '10

16 Dec '10

Welcome to issue 162 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of December 05 - 11. Wouter Swierstra [2]sent a call for papers for the ICFP 2011 to be held in Tokyo, Japan between September 19 - 21. The announcement contains all relevant dates of importance Dmitry Astapov [3]announced the realease of haskell-mpi, "a suite of Haskell bindings to the C MPI [Message Passing Interface] and convenience APIs on top of it." David Waern [4]annouced a new version of the venerable Haddock. "This version is compatible with .haddock files produced by the version of Haddock that comes with GHC 7.0.1." Michael Snoyman [5]announced the first release of his library and executable packdeps. "This is a library and executable containing the same functionality as the original packdeps website, namely letting you know when your version bounds exclude the use of the newest version of a library available." Michael also [6]announced the second major release of the mime-mail library. This "is a package providing support for rendering multipart emails." Jasper Van der Jeugt [7]announced the 0.0.2.0 release of the digestive functors library. "The library provides a general API to input consumption, and is an upgrade of formlets." So, what went on this week? Top Reddit Stories * Cartesian Closed Comic: Résumé Domain: ro-che.info, Score: 35, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/ekiao/cartesian_closed_comic_résum… Original: http://ro-che.info/ccc/11.html * GHC blog: An overhaul of stack management, and some performance improvements Domain: hackage.haskell.org, Score: 32, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/emabe/ghc_blog_an_overhaul_of_stac… Original: http://hackage.haskell.org/trac/ghc/blog/stack-chunks * How do You use Emacs for Haskell Development? Domain: self.haskell, Score: 29, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/ehl99/how_do_you_use_emacs_for_has… Original: /r/haskell/comments/ehl99/how_do_you_use_emacs_for_haskell_development/ * Library versus Framework: Yesod's Own World Domain: docs.yesodweb.com, Score: 26, Comments: 22 On Reddit: http://www.reddit.com/r/haskell/comments/ejgen/library_versus_framework_yes… Original: http://docs.yesodweb.com/blog/yesods-own-world/ * Visualizing Haskell types part II, Gin and monotonic : Inside T5 Domain: blog.ezyang.com, Score: 24, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/eiaef/visualizing_haskell_types_pa… Original: http://blog.ezyang.com/2010/12/gin-and-monotonic/ * Package of the day: parallel-io: combinators for sequencing IO actions onto a thread pool Domain: hackage.haskell.org, Score: 21, Comments: 15 On Reddit: http://www.reddit.com/r/haskell/comments/ehsqo/package_of_the_day_paralleli… Original: http://hackage.haskell.org/package/parallel-io-0.2.2 * Package of the day: haskell-mpi: Control.Parallel.MPI for high performance parallel (cluster) computations in Haskell Domain: hackage.haskell.org, Score: 19, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/ej5av/package_of_the_day_haskellmp… Original: http://hackage.haskell.org/package/haskell-mpi-1.0.0 * From Polymorphism To Polytypism Domain: zenzike.com, Score: 19, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/ejleb/from_polymorphism_to_polytyp… Original: http://zenzike.com/posts/2010-12-10-from-polymorphic-to-polytypic/ * Hussling Haskell types into Hasse diagrams : Inside T5 Domain: blog.ezyang.com, Score: 18, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/eh2zw/hussling_haskell_types_into_… Original: http://blog.ezyang.com/2010/12/hussling-haskell-types-into-hasse-diagrams/ * Building a business with Haskell: Case Studies: Cryptol, HaLVM and Copilot Domain: corp.galois.com, Score: 17, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/ejmwq/building_a_business_with_has… Original: http://corp.galois.com/blog/2010/12/10/building-a-business-with-haskell-cas… Top StackOverflow Questions * What is the benefit of purely functional data structure? votes: 15, answers: 4 Read on SO: http://stackoverflow.com/questions/4399837/what-is-the-benefit-of-purely-fu… * Haskell: Equation Expander 1+(1+(1+(1+(…))))=∞ votes: 9, answers: 2 Read on SO: http://stackoverflow.com/questions/4404663/haskell-equation-expander-1111 * Pure Functional Language: Haskell votes: 7, answers: 6 Read on SO: http://stackoverflow.com/questions/4382223/pure-functional-language-haskell * How does a haskell compiler works? votes: 7, answers: 4 Read on SO: http://stackoverflow.com/questions/4385160/how-does-a-haskell-compiler-works * Haskell typeclasses and C++ template classes votes: 7, answers: 6 Read on SO: http://stackoverflow.com/questions/4411279/haskell-typeclasses-and-c-templa… * Are there any special challenges for functional programming in an embedded environment? votes: 7, answers: 1 Read on SO: http://stackoverflow.com/questions/4418617/are-there-any-special-challenges… * Haskell: Where vs. Let votes: 6, answers: 3 Read on SO: http://stackoverflow.com/questions/4362328/haskell-where-vs-let * What are some good example haskell projects? votes: 6, answers: 2 Read on SO: http://stackoverflow.com/questions/4369962/what-are-some-good-example-haske… * Program Structure — Simple Commandline To Do List App — What's the Haskell way? votes: 6, answers: 2 Read on SO: http://stackoverflow.com/questions/4383512/program-structure-simple-command… * Learning to read haskell in english votes: 6, answers: 4 Read on SO: http://stackoverflow.com/questions/4393908/learning-to-read-haskell-in-engl… Quotes of the Week * kmc: it's great how laziness lets you ignore the order of evaluation except all the times when it doesn't * tg_: I can't wait until 100 years from now when 'eating food' will be deprecated from our lexicon in favor of 'oming noms' * kmc: maybe the 9,639,482nd time we argue about C++ we will finally resolve the issue * Berengal: * ddarius liked xmonad better when it was 90 lines... * Berengal liked xmonad better when it was on vinyl About the Haskell Weekly News New editions are posted to [8]the Haskell mailing list as well as to [9]the Haskell Sequence and [10]Planet Haskell. [11]RSS is also available, and headlines appear on [12]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18355 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18357 4. http://groups.google.com/group/fa.haskell/browse_thread/thread/b0c838a2249f… 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84141 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84142 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/84201 8. http://www.haskell.org/mailman/listinfo/haskell 9. http://sequence.complete.org/ 10. http://planet.haskell.org/ 11. http://sequence.complete.org/node/feed 12. http://haskell.org/

1 0

Gtk 0.12.0, Windows 7, Haskell Platform 2010.2.0.0, build error
by aditya siram 16 Dec '10

16 Dec '10

Hi all, I am having some issues building Gtk2Hs on Windows 7. It completes compiling the whole thing and then errors out with this message: Registering gtk-0.12.0... setup.exe: WARNING: cache is out of date: c:/Program Files/Haskell Platform/2010.2.0.0\lib\package.conf.d\package.cache use 'ghc-pkg recache' to fix. gtk-0.12.0: library-dirs: c:/devel/dist/win32/libpng-1.4.3-1/lib doesn't exist or isn't a directory (use --force to override) cabal.exe: Error: some packages failed to install: gtk-0.12.0 failed during the building phase. The exception was: ExitFailure 1 I'm not sure why it's looking at c:/devel/dist/win32/libpng-1.4.3-1/lib and I couldn't find any reference to this directory in the source tree. I tried to do a ghc-pkg recache but I get the follow permissions error: ghc-pkg.exe: c:/Program Files/Haskell Platform/2010.2.0.0\lib\package.conf.d\package.cache: you don't have permission to modify this file I changed this file to be world-writeable but with the same results. I get the same error if I try and cabal install gtk. Thanks for your help. -deech

1 0

installing gtk2
by Max Buchholz 15 Dec '10

15 Dec '10

1 0

par / pseq example
by J. Waldmann 15 Dec '10

15 Dec '10

I was trying to find an easy example for par/pseq, and I finally used plain mergesort ( on Prelude.[] ) and I observed that it is best to give +RTS -A1G (or more) such that there are only very few garbage collections. This roughly cuts execution time in half (from +RTS -N1 to -N4, on an i7 CPU) which is nice for a demonstration. The following is the very straightforward program that I use. Is it OK? I'm not asking for a faster sort algorithm, but whether par/pseq is used correctly/idiomatically in this program (so that students don't get a wrong impression). msort [] = [] ; msort [x] = [x] msort xs = let ( here, there ) = splitAt ( div ( length xs ) 2 ) xs mshere = msort here msthere = msort there in last mshere `par` last msthere `pseq` merge mshere msthere merge [] ys = ys ; merge xs [] = xs merge (x:xs) (y:ys) = if x < y then x : merge xs (y:ys) else y : merge (x:xs) ys Thanks - J.W.

1 0

lhs2tex build failure
by Permjacov Evgeniy 15 Dec '10

15 Dec '10

Hello! I use ghc-7.0.1 and cabal 1.10.0 . When tried to install lhs2tex-1.16 I got error in Setup.lhs: =============================== Setup.hs:294:46: `programArgs' is not a (visible) field of constructor `ConfiguredProgram' Setup.hs:296:46: `programArgs' is not a (visible) field of constructor `ConfiguredProgram' =============================== s/programArgs/programDefaultArgs/ resolves error (cabal changed ConfiguredProgram definition) however, later I had another problem when compiling: =============================== [16 of 19] Compiling MathPoly ( MathPoly.lhs, dist/build/lhs2TeX/lhs2TeX-tmp/MathPoly.o ) MathPoly.lhs:361:39: Ambiguous type variable `tok' in the constraint: (CToken tok) arising from a use of `mkFromTo' Probable fix: add a type signature that fixes these type variable(s) In the expression: mkFromTo fstack rn n rc [fromToken $ TeX False (indent (rn, rc) (n, c))] p ls In the expression: let rstack = dropWhile (\ (rc, _) -> rc >= c) stack (rn, rc) = findrel (n, c) rstack fstack = (c, l) : rstack in mkFromTo fstack rn n rc [fromToken $ TeX False (indent (rn, rc) (n, c))] p ls In a case alternative: Poly p@(((n, c), ts, ind) : rs) | first -> let rstack = dropWhile (\ (rc, _) -> ...) stack (rn, rc) = findrel ... rstack .... in mkFromTo fstack rn n rc [fromToken $ TeX False (indent (rn, rc) (n, c))] p ls | c `elem` z -> mkFromTo stack n (n ++ "E") c ts rs ls =============================== I cannot fix it on my own. Any suggestions ? Sorry, by I do not want downgrade, if possible.

2 1

Re: [Haskell-cafe] Functor => Applicative => Monad
by Max Bolingbroke 15 Dec '10

15 Dec '10

3, John Smith <voldermort(a)hotmail.com> wrote: > I would like to formally propose that Monad become a subclass of > Applicative I'm not in favour of this change because of the code breakage issue. However, I think that an acceptable plan (mentioned elsewhere on the list, but doesn't seem to have had any subsequent discussion) would be to introduce a GHC warning for such cases: "Warning: you are declaring a Monad instance for MyMonad without a corresponding Applicative instance. This will be an error in GHC 7.2" Then in 7.2 you can remove the warning and change the class hierarchy. (Substitute 7.4 for 7.2 if you think we need more time for library authors to update, or if you add the warning only to the 7.2 series). Cheers, Max

1 0

Iteratee-like
by Permjacov Evgeniy 15 Dec '10

15 Dec '10

Ok, I think, I made it right now. I wrote two versions of the very same module with roughly the same interface. It is minimalistic framework for producing, transforming, zipping and folding streaming data (a sample code that does file IO provided, but it is not well tested yet). One version abuses CPS-style, requires rank2types, but should be slightly faster and has cleaner code. Other version is plain haskell-98 and should be reasonable portable, but is tricky at some plases and still uses CPS for specifing stream processors. I want to add many things, but currently I want to document code properly so it be easy to read (BTW, has someone any article, produced from *.lhs with good typesetting and with *.lhs itself avaible? ) current links https://github.com/permeakra/Rank2Iteratee https://github.com/permeakra/PassiveIteratee The main difference from 'original' iteratees I read about is that both do not use 'chunks' and pass data one-by-one. So, what I wrote may be slower, but should be easier to maintain and more transparent for ghc optimising facilities. I wanted as clean and simple code as possible, but it is still very, very messy at some places and I want it cleaner. Any suggestions? I also want to check, how good ghc does its work with this messy modules. They may become interesting benchmarks.

1 0

Taking the TLS package for a spin ... and failing
by Mads Lindstrøm 15 Dec '10

15 Dec '10

Hi Haskellers, I am trying to connect a Java client to a Haskell server using the Haskell tls package, and things are not working out for me. There is a lot of steps involved and I do not know what I am doing wrong, so this is a long message. But first I create a private/public key-pair: > openssl genrsa -out privkey.pem 2048 then I make a self-signed certificate: > openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095 > Country Name (2 letter code) [AU]: > State or Province Name (full name) [Some-State]: > Locality Name (eg, city) []: > Organization Name (eg, company) [Internet Widgits Pty Ltd]: > Organizational Unit Name (eg, section) []: > Common Name (eg, YOUR name) []:192.168.1.6 > Email Address []: then I convert the certificate to DER format and stuff it into a Java keystore: > openssl x509 -in cacert.pem -out cert.der -outform DER > keytool -keystore myKeystore.store -importcert -storepass foobar -keypass foobar -file cert.der now I start the Haskell server: > ghc -hide-package monads-tf Server.hs -e main and then the Java client: > javac Client.java > java -Djavax.net.debug=all -Djavax.net.ssl.trustStore=myKeystore.store -Djavax.net.ssl.trustStorePassword=foobar Client >JavaClientOutput.txt 2>&1 The server output is: > <interactive>: user error (unexpected type received. expecting handshake ++ Left (Error_Packet "invalid type")) and not "Hello world" as expected. The client output is very long, but the most interesting part is properly: > main, received EOFException: error > main, handling exception: javax.net.ssl.SSLHandshakeException: Remote host closed connection during handshake > main, SEND TLSv1 ALERT: fatal, description = handshake_failure I have attached the Haskell server, the Java client and the full java output. Hope somebody can help figure out what I do wrong. I am using the Haskell tsl package version 0.3.1. And I run Debian Linux. I also tried connecting a Java client to a Java server. First create server keystore: > openssl pkcs8 -topk8 -nocrypt -in privkey.pem -inform PEM -out privkey.der -outform DER > java -Dkeystore=myServerKeystore.store ImportKey privkey.der cert.der ImportKey.java can be found here http://www.agentbob.info/agentbob/79-AB.html . then start Java server: > javac JavaServer.java > java -Djavax.net.ssl.keyStore=myServerKeystore.store -Djavax.net.ssl.keyStorePassword=importkey JavaServer and run the client again: > java -Djavax.net.debug=all -Djavax.net.ssl.trustStore=myKeystore.store -Djavax.net.ssl.trustStorePassword=foobar Client and the server outputs: > Hello world as expected. Thus I think the certificates are fine, and the Java client is fine. But what am I doing wrong in the Haskell server? I have attached JavaServer.java. Regards, Mads Lindstrøm

3 7

CBRef, a wrapper around IORef with callbacks
by Dmitry V'yal 14 Dec '10

14 Dec '10

Hello, while building GUIs using Gtk2HS I always struggled with the following question: how to sync the state of the GUI with the state of the rest application. I usually make several IORefs store the state there. But it's quite easy to forget to update relevant parts of GUI when state changes, especially then it's done in several places, say, by user's request and by some internal event. Some time ago I realized a pattern which proved to be useful for me several times. I wrapped IORef in a type: data CBRef a = CBRef {v_ref :: IORef a, callbacks :: IORef [a -> IO()] } now I add callbacks using addCB :: CBRef a -> (a -> IO()) -> IO () addCB r cb = modifyIORef (callbacks r) (++[cb]) which fires then the value is changed: writeCBRef :: CBRef a -> a -> IO () writeCBRef r v = do writeIORef (v_ref r) v cbs <- readIORef (callbacks r) mapM_ ($ v) cbs all the remaining IORef-like interface is present too. By using these callbacks for updating GUI I can be sure all it's parts are in sync. I suspect it's a special case of more general idea. Can anyone give a hint? Also, do you think it's useful enough to be uploaded to Hackage? Or maybe something similar is already there? How do you organize your GUI applications? Best wishes, Dmitry

1 0

Re: [Haskell-cafe] Conditional compilation for different versions of GHC?
by Brandon S Allbery KF8NH 14 Dec '10

14 Dec '10

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 12/7/10 06:00 , Henning Thielemann wrote: > Brandon S Allbery KF8NH wrote: >> Since the base package is (with good reason) part of the compiler, anyone >> smart enough to get that to work is smart enough to edit the cabal file. > > There are good reasons for not only bundling 'ghc' package with GHC, but > 'base', too? I assumed it is intended to untangle 'base' and GHC in future, > such that 'base' can be used with JHC, UHC, Hugs. I seem to recall that the logistics of that change have been proving a bit difficult in practice, and as such it's probably not going to happen very soon. - -- brandon s. allbery [linux,solaris,freebsd,perl] allbery(a)kf8nh.com system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkz+9HYACgkQIn7hlCsL25XXPQCfa/x9ZyhUmN88vu3/EPv8Tjhq +5EAniBq3G9gto/IC8kyYFP2rAjTxB/4 =LnDx -----END PGP SIGNATURE-----

3 2

Re: [Haskell-cafe] [Haskell] Functor => Applicative => Monad
by Conor McBride 14 Dec '10

14 Dec '10

[switching to cafe] On 14 Dec 2010, at 08:59, Sittampalam, Ganesh wrote: > John Smith wrote: >> I would like to formally propose that Monad become a subclass of >> Applicative, with a call for consensus by 1 February. > > I would prefer that we have some proposal like class aliases > implemented > before we start fundamental restructuring of basic type classes. This > would help to limit the disruption these changes cause, which will be > substantial. I'm inclined to agree. What's even more galling than not having Functor and Applicative instances for Monads is having to write them! At the very least, can we open this particular vessel of vermicular splendidity and verify that the inmates are still grinning with persistence? If I recall, the class alias proposal was rather more ambitious than necessary to solve this problem (though that is no crime), but still a little wrinkled in the corners. Looking at the relevant webpages, I see the proposal has lots of attractive motivational examples, but less by way of definition. But perhaps, somewhere, it has been defined enough for a prototype? It's surely worth looking at some way to define default instances for superclasses, provided they can be overridden or switched off. Where did this train of though leave the rails, again? Cheers Conor

1 0

Re: [Haskell-cafe] Offer to mirror Hackage
by Brandon Moore 14 Dec '10

14 Dec '10

On Dec 13, 2010, at 6:15 PM, wren ng thornton <wren(a)freegeek.org> wrote: On 12/13/10 8:25 AM, Paul Sargent wrote: How about, as a cheep and cheerful method to get up running. If the premise is that the original server is trustworthy and the mirrors aren't, then: 1) Hash all packages on the original server. 2) Hash goes into a side car file (e.g.<packagename>.sha) that lives next to the package If hashed are added to the package information "cabal update" downloads, installing packages from mirrors will continue to work during a central outage. I still contend that we shouldn't have to trust the central server either. The hash can be created alongside the sdist on the maintainer's computer, and then both are uploaded to central. Thus, the maintainer can verify that the hash on central matches their own, which ensures that: For now, it's enough to find a simple scheme where adding untrusted mirrors is no worse than the current situation. Hashes seem to work for that: 1. cabal update always reads from the central server (if uploads are impossible when the central server is down, the package lit won't even get stale) 2. The package descriptions are extended with hashes 3. Cabal may download packages from mirrors, but checks the hash. Your proposal doesn't narrow trust to the maintainers (which is currently open to the public anyway), because an adversary as described could return the correct hash and package for the maintainer, and the corrupted version to others. Brandon

2 1

[ANNOUNCE] haskell-mpi-1.0.0
by Dmitry Astapov 14 Dec '10

14 Dec '10

Dear Haskellers, We are pleased to announce the release of haskell-mpi-1.0.0, a suite of Haskell bindings to the C MPI library and convenience APIs on top of it. About MPI --------- MPI, the Message Passing Interface, is a popular communications protocol for distributed parallel computing (http://www.mpi-forum.org/) MPI applications consist of independent computing processes which share information by message passing. It supports both point-to-point and collective communication operators, and manages much of the mundane aspects of message delivery. There are several high-quality implementations of MPI available, all of which conform to the standard API specification (the latest version of which is 2.2). The MPI specification defines interfaces for C, C++ and Fortran, and bindings are available for many other programming languages. About Haskell-MPI ----------------- As the name suggests, Haskell-MPI provides a Haskell interface to MPI, and thus facilitates distributed parallel programming in Haskell. It is implemented on top of the C API via Haskell's foreign function interface. Haskell-MPI provides three different ways to access MPI's functionality: * A direct binding to the C interface (see Control.Parallel.MPI.Internal). * A convenient interface for sending arbitrary serializable Haskell data values as messages (see Control.Parallel.MPI.Simple). * A high-performance interface for working with (possibly mutable) arrays of storable Haskell data types (see Control.Parallel.MPI.Fast). We do not currently provide exhaustive coverage of all the functions and types defined by MPI 2.2, although we do provide bindings to the most commonly used parts. In future we plan to extend coverage based on the needs of projects which use the library. The package is available from http://hackage.haskell.org/package/haskell-mpi. Examples and comprehensive testsuite are included in the source distribution. Code was tested on 32- and 64-bit platforms, with MPICH2 and OpenMPI. The Fast API shows performance comparable to C, and the Simple API is generally 2-7 time slower due to (de)serialization overhead and necessity to issue additional MPI requests behind the curtains in some cases. Bernie Pope started this project as a rewrite of hMPI which was written by Michael Weber and Hal Daume III. He was later joined by Dmitry Astapov, working on the library as part of Well-Typed LLP's Parallel Haskell Project. Development is happening on GitHub, in git://github.com/bjpop/haskell-mpi. Please join in! Sincerely yours, Dmitry Astapov, Bernie Pope -- Dmitry Astapov Well-Typed LLP, http://www.well-typed.com/

3 2

Re: [Haskell-cafe] admission to graduate program in CS
by Johann Bach 14 Dec '10

14 Dec '10

Can I get some recommendations for CS textbooks to study for the CS GRE? Note that I am already fluent in C++ and Python (and getting better at Haskell), so I don't need hand-holding in learning the very basics... however, I do need to review the standard theory. For example, if the GRE asks: "What are the fundamental elements of OO?" I'm actually not sure what the answer is. (There's a difference between using an OO language, and talking about the theory behind it. In garden-variety programming we never talk about the theory.) I assume that any textbook is going to include the basics---I can skim through those parts. But I would be curious if there is a textbook that quickly gets into the deep stuff (and is particularly relevant to the GRE). Thanks, J

2 1

Conditional compilation for different versions of GHC?
by Jinjing Wang 14 Dec '10

14 Dec '10

Dear list, >From ghc 7.0.1 release notes: > The Language.Haskell.TH.Quote.QuasiQuoter type has two new fields: quoteType and quoteDec. Some of my code needs to be conditionally compiled to support both version 6 and 7, what is the recommended way to do it? ref: * http://new-www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.ht… -- jinjing

9 18

Monad Syntax
by caseyh＠istar.ca 14 Dec '10

14 Dec '10

From: A Neighborhood of Infinity Monday, August 07, 2006 You Could Have Invented Monads! (And Maybe You Already Have.) http://blog.sigfpe.com/2006/08/you-could-have-invented-monads-and.html The following part: do let x = 7 y <- Writer (x+1,"inc\n") z <- Writer (2*y,"double\n") Writer (z-1,"dec\n") The notation is very suggestive. When we write y <- ... it's as if we can pretend that the expression on the right hand side is just x+1 and that the side-effect just looks after itself. Why pretend? Couldn't the syntax be: do let x = 7 y <- x+1, Writer ("inc\n") z <- 2*y, Writer ("double\n") z-1, Writer ("dec\n") Or some other delimiter than the comma? I'm thinking this syntax might be easier to understand. :)

3 2

Weird error during derive-2.3.0.2 build
by Alex 13 Dec '10

13 Dec '10

Hi all. I am trying to install the "yi" editor using cabal-install, which in turns installs the package 'derive-2.3.0.2'. I get the following error during derive's compilation: [53 of 58] Compiling Data.Derive.Internal.Traversal ( Data/Derive/Internal/Traversal.hs, dist/build/Data/Derive/Internal/Traversal.o ) Data/Derive/Internal/Traversal.hs:34:0: Illegal instance declaration for `Applicative (Writer w)' (All instance types must be of the form (T t1 ... tn) where T is not a synonym. Use -XTypeSynonymInstances if you want to disable this.) In the instance declaration for `Applicative (Writer w)' cabal: Error: some packages failed to install: derive-2.3.0.2 failed during the building phase. The exception was: ExitFailure 1 Of course, I tried to build it with --ghc-option=-XTypeSynonymInstances, which in turn gives another compilation error. I am using ubuntu maverick 32-bit, with ghc-6.12.1 and cabal-install 0.8.2. The ghc was installed from the package repository. Cabal was installed using: cabal-install cabal Alex.

3 2

Connecting to a running Haskell program using GHCI
by aditya siram 13 Dec '10

13 Dec '10

Hi all, I'd like to load a Haskell program into GHCi A and then connect to GHCi A from GHCI B. Is there any way to do this? This would be handy (handier than telnet) for demoing and debugging server applications that use shared resources. -deech

1 0

Re: [Haskell-cafe] [Haskell] reference to DoCon
by Henning Thielemann 13 Dec '10

13 Dec '10

On Mon, 13 Dec 2010, Serge D. Mechveliani wrote: > Dear administration of www.haskell.org, > > (I am sorry for not finding a more appropriate list for this letter) > > In old days, my program system DoCon > > (computer algebra written in Haskell) had its copy on > www.haskell.org/docon/ > -- if I remember correct. It certainly disappeared on the server migration 2010-11-30. That's not nice. A solution will certainly be to move www.haskell.org/docon/ to community.haskell.org/docon/ and set a redirection from www.haskell.org/docon/.

1 0

Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions
by John Lato 13 Dec '10

13 Dec '10

From: oleg(a)okmij.org > > Just for the record: the library IterateeM.hs, uses NO extensions to > Haskell98, let alone Haskell2010. The library as written requires > LowLevelIO.hs, which uses FFI (which has been Haskell98 addendum and > is in proper Haskell2010). The sample code, Wc.hs, for example, is > Haskell98. So, the iteratee can be written with no extensions > whatsoever. > Related to this, IterateeM.hs and LowLevelIO.hs don't use runtime exceptions either, which I consider a particularly nice feature. > > In particular, IterateeM does not use any monad transformer library > (although it could have). I found that the trouble of writing a state > monad for a particular state is negligible compared to the pain of > choosing a particular monad transformer library, and especially the > pain inflicted on the users who have to deal with many a conflicts of > monad transformer libraries. > > > > The problem was that I wished Zippee. It means that external enumerator > > must be "suspended" at some points so Zippee can process elements from > > both left and right streams in desired order. It makes any other > > approach I considered impossible to use. > > The file IterateeN.hs demonstrates zipping two streams together (in > lock-step and not in-lockstep). It turns out, the existing Iteratee > interface and type suffices. This is described in more detail in: > > Parallel composition of iteratees: one source to several sinks > http://okmij.org/ftp/Streams.html#1enum2iter > > Parallel composition of streams: several sources to one sink > http://okmij.org/ftp/Streams.html#2enum1iter > It seems I was mistaken in my last reply. That's what I get for answering before I read through all my weekend email. John

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admission to graduate program in CS
by Johann Bach 13 Dec '10

13 Dec '10

Hello list, I am a programmer who just got laid off. I have been studying Haskell and learning a lot about CS, *as a hobby*. I have a B.S. from Caltech in engineering (didn't take many CS classes). Now that my options are open, I'd like to think about graduate school in CS which is probably the academic subject I love most in the world. But I didn't take many CS classes in college, and my job was garden-variety programming, mostly to someone else's design and process rules. My real CS experience comes from my hobbies such as learning Haskell. But that leaves me without a way to prove my ability, at least not by showing recent schoolwork or having any recommendations from CS professors. I hardly know anything about how graduate schools evaluate candidates. So what I am wondering is, could I use a demonstration of my self-study to demonstrate ability? I'm not sure what form that would take, but I'm just trying to look at every angle right now. Thanks, Johann

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threadWaitRead and threadWaitWrite on multiple fds
by Mathijs Kwik 13 Dec '10

13 Dec '10

Hi all, I read the paper about the new ghc7 event handling IO manager goodies. This is all very exciting stuff. I didn't know GHC's RTS had these smart async-IO facilities. The paper pointed me at threadWaitRead/threadWaitWrite. While very nice the way they are, I would also like to be able to wait on more than 1 fd until 1 of them becomes available. Would it be possible to create this functionality myself? Or do I need to request it and wait for a new GHC? It looks like the functionality I need is in System/Event/Thread. I think I can manage to write my own version of those functions which then loop through a list of fds, but the original file imports System/Event/Manager (registerFd, unregisterFd_) which I can't do because it's a hidden module. Is there a way around this? Thanks, Mathijs

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Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions
by John Lato 13 Dec '10

13 Dec '10

From: Permjacov Evgeniy <permeakra(a)gmail.com> > > Hi. I Wrote a simple iteration library. It was not intensively tested, > so it MAY contatin bugs, but it is very unlikely. The library is > currently on github: https://github.com/permeakra/iteration > > I'm not ready to upload it to hackage, as some testing and extension is > really needed. However, I'd like to know about possible flaws. > > Current goal is addition of byte-stream (de)compression and IO functions > extenstion. After this package will be cabalized and uploaded to > hackage. So, while design is not frozen yet, I'm interested in criticism > -)/ > First, I haven't examined your code in sufficient depth to fully understand it, so I may be off the mark with this comment. However, I'm not convinced it's possible to safely implement zipping in iteration-style IO without another technique (e.g. monadic regions), by which I mean I suspect any code which exposes enough control to pause an enumeration (or alternatively allows a user-supplied termination check to the enumerator) will also not provide guaranteed finalization/garbage collection of the underlying resource (e.g. handle). I also require zipping of streams, and in fact it is possible with iteratee. I haven't included the code in the library because I was formerly not convinced of its safety. I do think it's safe now, but only by use of a monadic region. John

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Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions
by oleg＠okmij.org 13 Dec '10

13 Dec '10

Just for the record: the library IterateeM.hs, uses NO extensions to Haskell98, let alone Haskell2010. The library as written requires LowLevelIO.hs, which uses FFI (which has been Haskell98 addendum and is in proper Haskell2010). The sample code, Wc.hs, for example, is Haskell98. So, the iteratee can be written with no extensions whatsoever. In particular, IterateeM does not use any monad transformer library (although it could have). I found that the trouble of writing a state monad for a particular state is negligible compared to the pain of choosing a particular monad transformer library, and especially the pain inflicted on the users who have to deal with many a conflicts of monad transformer libraries. > The problem was that I wished Zippee. It means that external enumerator > must be "suspended" at some points so Zippee can process elements from > both left and right streams in desired order. It makes any other > approach I considered impossible to use. The file IterateeN.hs demonstrates zipping two streams together (in lock-step and not in-lockstep). It turns out, the existing Iteratee interface and type suffices. This is described in more detail in: Parallel composition of iteratees: one source to several sinks http://okmij.org/ftp/Streams.html#1enum2iter Parallel composition of streams: several sources to one sink http://okmij.org/ftp/Streams.html#2enum1iter

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gtk2hs and hmake websites
by Joachim Breitner 13 Dec '10

13 Dec '10

Hi, I get regular error message from some Debian tools that check for new upstream versions that it cannot find http://haskell.org/hmake, and http://haskell.org/gtk2hs seems to be gone as well since the recent move of haskell.org. Is that temporary or will these projects have to find new homes? Greetings, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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The Monad Reader links are broken
by Jason Dagit 12 Dec '10

12 Dec '10

Hello, I noticed today that the links in this article point to Haskell.org and they are broken: http://themonadreader.wordpress.com/previous-issues/ Maybe someone can fix this? Thanks! Jason

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Avoiding the Y combinator for self-referencing types
by Florian Weimer 12 Dec '10

12 Dec '10

Suppose I've got some named objects which reference other objects by name: > data NodeS = NodeS {nameS :: String, refsS :: [String]} Through name resolution, the strings are translated to the actual nodes they denote: > data Node = Node {name :: String, refs :: [Node]} > resolve :: [NodeS] -> Map String Node NodeS and Node are quite similar, so they should probably be the same parametrized type. However, if I turn the type of the references into a type parameter, I need the type-level Y combinator to avoid an infinite type, and manipulating nodes turns a bit more tedious because of increased syntactic overhead. Is there a third choice, beyond manually expanding the type definition or using Y?

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