April 2015 - Haskell-Cafe

Is there a name for this algebraic structure?
by Gleb Peregud 24 Apr '15

24 Apr '15

Hello I am wondering if there's a well known algebraic structure which follows the following patterns. Let's call it S: It's update-able with some opaque "a" (which can be an element or an operation with an element): update :: S -> a -> S There's a well defined zero for it: empty :: S Operations on it are idempotent: update s a == update (update s a) a Every S can be reconstructed from a sequence of updates: forall s. exists [a]. s == foldl update empty [a] An example of this would be Data.Set: empty = Set.empty update = flip Set.insert Is there something like this in algebra? Cheers, Gleb

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low-cost matrix rank?
by Mike Meyer 24 Apr '15

24 Apr '15

Noticing that diagrams 1.3 has moved from vector-space to linear, I decided to check them both for a function to compute the rank of a matrix. Neither seems to have it. While I'm doing quite a bit of work with 2 and 3-element vectors, the only thing I do with matrices is take their rank, as part of verifying that the faces of a polyhedron actually make a polyhedron. So I'm looking for a relatively light-weight way of doing so that will work with a recent (7.8 or 7.10) ghc release. Or maybe getting such a function added to an existing library. Anyone have any suggestions? Thanks, Mike

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Re: [Haskell-cafe] Space leak with recursion
by Martijn Rijkeboer 24 Apr '15

24 Apr '15

>> pollSockets :: State -> IO () >> pollSockets state = >> void $ poll (-1) >> [ Sock (listenSocket state) [In] (Just $ observerHandleEvts >> state) >> , Sock (snapSocket state) [In] (Just $ snapshotHandleEvts >> state) >> ] >> >> >> observerHandleEvts :: State -> [Event] -> IO () >> observerHandleEvts state _ = do >> void $ receiveMulti $ listenSocket state >> pollSockets state >> >> >> snapshotHandleEvts :: State -> [Event] -> IO () >> snapshotHandleEvts state _ = do >> void $ receiveMulti $ snapSocket state >> pollSockets state > > What happens here if there is an event waiting on both the listen > socket *and* the snap socket? It looks like `observerHandleEvts` > will be called and, since it recursively calles `pollSockets`, > the `snapshotHandleEvts` handler will not be run, although its > continuation will be kept around leaking space. This could be an issue, but during my testing there were no messages sent to the snapshot socket (I haven't implemented the snapshot socket in the client yet). > It seems unwise to make a recursive call to the event loop inside a > handler. How would I update my state and ensure that the next invocation of a handler gets the updated state? With the forever function my state updates are not propagated. Kind regards, Martijn Rijkeboer

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Space leak with recursion
by Martijn Rijkeboer 24 Apr '15

24 Apr '15

Hi, I'm trying to make an observable (code below) that listens to two ZeroMQ sockets and publishes the received messages on a third. Every message that is received gets an incremented sequence number before it is send on the publishing socket. To keep the current sequence number a state object is passed to the polling function and after handling the message, the polling function is called again with the updated state. Unfortunately this recursive calling of the polling function creates a space leak. Any suggestions how to fix this? Note: for brevity I left the incrementing of the sequence number and the sending on the publishing socket out of the code. Kind regards, Martijn Rijkeboer --- Code --- module Observable ( run ) where import Control.Monad (void) import Data.Int (Int64) import System.ZMQ4 data State = State { nextSeqNum :: !Int64 , listenSocket :: !(Socket Pull) , publishSocket :: !(Socket Pub) , snapSocket :: !(Socket Router) } run :: IO () run = do withContext $ \ctx -> withSocket ctx Pull $ \observer -> withSocket ctx Pub $ \publisher -> withSocket ctx Router $ \snapshot -> do setLinger (restrict (0::Int)) observer bind observer "tcp://*:7010" setLinger (restrict (0::Int)) publisher bind publisher "tcp://*:7011" setLinger (restrict (0::Int)) snapshot setSendHighWM (restrict (0::Int)) snapshot bind snapshot "tcp://*:7013" let state = State { nextSeqNum = 0 , listenSocket = observer , publishSocket = publisher , snapSocket = snapshot } pollSockets state pollSockets :: State -> IO () pollSockets state = void $ poll (-1) [ Sock (listenSocket state) [In] (Just $ observerHandleEvts state) , Sock (snapSocket state) [In] (Just $ snapshotHandleEvts state) ] observerHandleEvts :: State -> [Event] -> IO () observerHandleEvts state _ = do void $ receiveMulti $ listenSocket state pollSockets state snapshotHandleEvts :: State -> [Event] -> IO () snapshotHandleEvts state _ = do void $ receiveMulti $ snapSocket state pollSockets state

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[ANN]: the Helium compiler, version 1.8.1
by Jurriaan Hage 24 Apr '15

24 Apr '15

Dear all, we have recently uploaded Helium 1.8.1, the novice friendly Haskell compiler, to Hackage. Improvements in this version - Helium can again work together with our Java-based programming environment Hint. The jar file for Hint itself can be downloaded from the Helium website at: http://foswiki.cs.uu.nl/foswiki/Helium which also has some more documentation on how to use Hint and helium. - the svn location if you are interested in the sources is now the correct one To install Helium simply type cabal install helium cabal install lvmrun Helium compiles with GHC 7.6.3 and 7.8.x, but does not yet compile with 7.10. Any questions and feedback are welcome at helium(a)cs.uu.nl. best regards, The Helium Team

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ANN: dns-server: forward DNS queries to StatDNS REST API
by Erik Dominikus 23 Apr '15

23 Apr '15

Bad news: ISP is intercepting packets to UDP port 53. Good news: There is DNS resolution over HTTP (http://www.statdns.com/api/) Bad news: The software bridging DNS clients and that HTTP service is missing. Good news: I made (a small but working part of) it. I've been using it on my computer. The code is here: https://github.com/edom/dns-server

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CFP: FHPC 2015: Workshop on Functional High-Performance Computing [w/ICFP]
by Trevor McDonell 23 Apr '15

23 Apr '15

Apologies if you receive this message more than once. ====================================================================== CALL FOR PAPERS FHPC 2015 The 4th ACM SIGPLAN Workshop on Functional High-Performance Computing Vancouver, British Columbia, Canada, Canada September 3, 2015 https://sites.google.com/site/fhpcworkshops/ Co-located with the International Conference on Functional Programming (ICFP 2015) Submission Deadline: Friday, 15 May, 2015 (anywhere on earth) ====================================================================== The FHPC workshop aims at bringing together researchers exploring uses of functional (or more generally, declarative or high-level) programming technology in application domains where high performance is essential. The aim of the meeting is to enable sharing of results, experiences, and novel ideas about how high-level, declarative specifications of computationally challenging problems can serve as maintainable and portable code that approaches (or even exceeds) the performance of machine-oriented imperative implementations. All aspects of performance critical programming and parallel programming are in-scope for the workshop, irrespective of hardware target. This includes both traditional large-scale scientific computing (HPC), as well as work targeting single node systems with SMPs, GPUs, FPGAs, or embedded processors. It is becoming apparent that radically new and well founded methodologies for programming such systems are required to address their inherent complexity and to reconcile execution performance with programming productivity. Proceedings: ============ Accepted papers will be published by the ACM and will appear in the ACM Digital Library. * Submissions due: Friday, 15 May, 2015 (anywhere on earth) * Author notification: Friday, 26 June, 2015 * Final copy due: Sunday, 19 July, 2015 Submitted papers must be in portable document format (PDF), formatted according to the ACM SIGPLAN style guidelines (2 column, 9pt format). See http://www.sigplan.org/authorInformation.htm for more information and style files. Typical papers are expected to be 8 pages (but up to four additional pages are permitted). Contributions to FHPC 2015 should be submitted via Easychair, at the following URL: * https://www.easychair.org/conferences/?conf=fhpc15 The submission site is now open. The FHPC workshops adhere to the ACM SIGPLAN policies regarding programme committee contributions and republication. Any paper submitted must adhere to ACM SIGPLAN's republication policy. PC member submissions are welcome, but will be reviewed to a higher standard. http://www.sigplan.org/Resources/Policies/Review http://www.sigplan.org/Resources/Policies/Republication Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC programme, see its web page (http://www.sigplan.org/PAC.htm) Programme Committee: ==================== Tiark Rompf (co-chair) Purdue University, USA Geoffrey Mainland (co-chair) Drexel University, USA Kevin Brown Stanford University, USA James Cheney University of Edinburgh, UK Albert Cohen INRIA, France David Duke University of Leeds, UK Yukiyoshi Kameyama University of Tsukuba, Japan Gabriele Keller University of New South Wales, Australia Paul H J Kelly Imperial College London, UK Trevor L. Mcdonell Indiana University, USA Greg Michaelson Heriot-Watt University, UK Cosmin E. Oancea University of Copenhagen, Denmark Markus Pueschel ETH Zurich, Switzerland Sukyoung Ryu KAIST, Korea Alexander Slesarenko Huawei, Russia Josef Svenningsson Chalmers University of Technology, Sweden

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How to use an crypto with hackage cereal?
by Magicloud Magiclouds 23 Apr '15

23 Apr '15

Hi, I am trying to work with some binary data that encrypted by field instead of the result of serialization. I'd like to use Data.Serialize to wrap the data structure. But I could not figure out how to apply an runtime specified cipher method to the bytestring. Any idea? Or I should use totally other solution? Thanks. -- 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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compiling GHC 7.8 on raspberry pi
by Sven Bartscher 23 Apr '15

23 Apr '15

Greetings, I'm trying to get a haskell program to run on a raspberry pi (running raspbian). Unfortunately it requires template haskell. Since the GHC included in raspbian wheezy doesn't support TH I'm trying to compile GHC 7.8.4 on the rpi. Most of the compilation worked fine. I got problems with the memory consumption, but adding a lot of swapspace solved this problem. During the final phase the compilation process complains about a "strange closure type 49200" (the exact number is varying, but most often it's 49200). Does anyone here have experience, how to compile GHC 7.8 on a raspberry pi? As a side note: The compilation is running in QEMU while the compiled program should run on a real rpi. Regards Sven

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[FUN] Cheryl's birthday; solved using Haskell/SBV
by Levent Erkok 23 Apr '15

23 Apr '15

For those of us who'd rather have Haskell do the thinking for us: https://gist.github.com/LeventErkok/654a86a3ec7d3799b624 Honestly, this is more an exercise in how to formalize such puzzles as opposed to demonstrating the capabilities of SBV or SMT-solvers in general; but fun nonetheless. The backend SMT solver (I used Z3) solves the puzzle instantly. Enjoy.. -Levent. PS. Thanks to Amit Goel for suggesting the formalization strategy used in the encoding.

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