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creating standalone executable with haskell
by Damien Mattei 06 Mar '19

06 Mar '19

i want to run Haskell code on a system i'm not administrator??? if i compile my haskell program rather than use interpreter (i never compile it) can i run the executable on another Linux platform which has nothing of haskell installed on it ( no runtime library,etc...) ? i already did that with Racket Scheme could it be done with GHC compiler or should i ask the system admin to install haskell platform? regards, damien

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Second call for papers, MPC 2019, Portugal
by Graham Hutton 05 Mar '19

05 Mar '19

Dear all, The next Mathematics of Program Construction (MPC) conference will be held in Portugal in October 2019, co-located with the Symposium on Formal Methods (FM). Paper submission is 3rd May 2019. Please share, and submit your best papers! Best wishes, Graham Hutton Program Chair, MPC 2019 ====================================================================== *** SECOND CALL FOR PAPERS -- MPC 2019 *** 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with Formal Methods 2019 https://tinyurl.com/MPC-Porto ====================================================================== TIMELINE: Abstract submission 26th April 2019 Paper submission 3rd May 2019 Author notification 14th June 2019 Camera ready copy 12th July 2019 Conference 7-9 October 2019 KEYNOTE SPEAKERS: Assia Mahboubi INRIA, France Annabelle McIver Macquarie University, Australia BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). SCOPE: MPC seeks original papers on mathematical methods and tools put to use in program construction. Topics of interest range from algorithmics to support for program construction in programming languages and systems. Typical areas include type systems, program analysis and transformation, programming language semantics, security, and program logics. The notion of a 'program' is interpreted broadly, ranging from algorithms to hardware. Theoretical contributions are welcome, provided that their relevance to program construction is clear. Reports on applications are welcome, provided that their mathematical basis is evident. We also encourage the submission of 'programming pearls' that present elegant and instructive examples of the mathematics of program construction. SUBMISSION: Submission is in two stages. Abstracts (plain text, maximum 250 words) must be submitted by 26th April 2019. Full papers (pdf, formatted using the llncs.sty style file for LaTex) must be submitted by 3rd May 2019. There is no prescribed page limit, but authors should strive for brevity. Both abstracts and papers will be submitted using EasyChair. Papers must present previously unpublished work, and not be submitted concurrently to any other publication venue. Submissions will be evaluated by the program committee according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. Accepted papers must be presented in person at the conference by one of the authors. The proceedings of MPC 2019 will be published in the Lecture Notes in Computer Science (LNCS) series, as with all previous instances of the conference. Authors of accepted papers will be expected to transfer copyright to Springer for this purpose. After the conference, authors of the best papers from MPC 2019 and MPC 2015 will be invited to submit revised versions to a special issue of Science of Computer Programming (SCP). For any queries about submission please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. PROGRAM COMMITTEE: Patrick Bahr IT University of Copenhagen, Denmark Richard Bird University of Oxford, UK Corina Cîrstea University of Southampton, UK Brijesh Dongol University of Surrey, UK João F. Ferreira University of Lisbon, Portugal Jennifer Hackett University of Nottingham, UK William Harrison University of Missouri, USA Ralf Hinze University of Kaiserslautern, Germany Zhenjiang Hu National Institute of Informatics, Japan Graham Hutton (chair) University of Nottingham, UK Cezar Ionescu University of Oxford, UK Mauro Jaskelioff National University of Rosario, Argentina Ranjit Jhala University of California, USA Gabriele Keller Utrecht University, The Netherlands Ekaterina Komendantskaya Heriot-Watt University, UK Chris Martens North Carolina State University, USA Bernhard Möller University of Augsburg, Germany Shin-Cheng Mu Academia Sinica, Taiwan Mary Sheeran Chalmers University of Technology, Sweden Alexandra Silva University College London, UK Georg Struth University of Sheffield, UK CONFERENE VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Douro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISERS: José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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cannot catch exception
by Kees Bleijenberg 04 Mar '19

04 Mar '19

Hi all, The program reads lots of small Text files. readCDFile handles the encoding. Below is the simplest version of readCDFile. If I call readCDFile "/home/kees/freeDB/inputError/" "blah" (the file blah does not exist) I get: Left "MyError: /home/kees/freeDB/inputError/blah: openBinaryFile: does not exist (No such file or directory)". The exception is caught by exceptionHandler If I call readCDFile "/home/kees/freeDB/inputError/" "67129209" I get freeDB: Cannot decode byte '\xa0': Data.Text.Internal.Encoding.decodeUtf8: Invalid UTF-8 stream. The exception is not caught by exceptionHandler (No "MyError: " in front). The file 67129209 is indeed bad encoded. I'am using SomeException. Still, this 'bad encoding exception' is not caught. Why? Kees import qualified Data.Text as T import System.FilePath.Posix import qualified Data.Text.Encoding as TE import qualified Data.ByteString.Lazy as B import Prelude hiding (catch) import Control.Exception main :: IO () main = do res <- readCDFile "/home/kees/freeDB/inputError/" "67129209" print res readCDFile :: FilePath -> FilePath -> IO (Either String T.Text) readCDFile baseDir fn = do catch ( do buffer <- B.readFile (combine baseDir fn) let bufferStrict = B.toStrict buffer return $ Right $ TE.decodeUtf8 bufferStrict ) exceptionHandler exceptionHandler :: SomeException -> IO (Either String T.Text) exceptionHandler e = do let err = show e return $ Left $ "MyError: " ++ err --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. https://www.avast.com/antivirus

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Haskell wiki account request response time
by Howard B. Golden 04 Mar '19

04 Mar '19

Hi Michal, You requested a Haskell wiki account at Fri, 1 Mar 2019 16:08:10 +0100 > Date: Fri, 1 Mar 2019 16:08:10 +0100 > From: Miguel <m.i(a)gmx.at> > To: wiki-account-request(a)haskell.org > Subject: wiki-account-request > oo_miguel Then, 8 minutes, 25 seconds later, you sent this message to Haskell-Cafe: > From: m.i at gmx.at (Miguel) > Date: Fri, 1 Mar 2019 16:16:35 +0100 > Subject: [Haskell-cafe] wiki-account-request > Message-ID: <20190301151635.kkpq2m4x7fkbftqj(a)megaloman.softwarefools.com> > Hi, > Not receiving any response from the other channel I hereby request a > wiki.haskell.org account with the preferred username: "oo_miguel" > Thanks in Advance, > Michal Idziorek > Ref: > https://wiki.haskell.org/index.php?title=Special:UserLogin > "If you would like an account please email 'wiki-account-request' > (at the domain haskell dot org) or, if you find that unresponsive, > on the haskell-cafe mailing list." At Fri, 1 Mar 2019 18:36:00 +0100, Henk-Jan_van_Tuyl created your account. This was 2 hours and 28 minutes after your initial request. Generally, we create accounts within 24 hours of their request, often much sooner. All of us who create accounts are volunteers. We create accounts manually to prevent spam. Regards, Howard

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PR to "double-conversion"
by Иван Николаев 02 Mar '19

02 Mar '19

Hi Bryan! May I ask you to take a look at my PR to your double-conversion library? I’ve made it about six months ago and sent you an email. A few days ago I updated it. In the PR mentioned above I’m adding several things which need your attention: 1. Conversion to bytestring and text builder. 2. Conversion of Float (using type family, but without performance degrading). 3. More benchmarks. 4. Update of the original double-conversion library. Now a bunch of 20k doubles is converted to strict bytestring in 5-8 ms using bytestring builder instead of >200-300ms using just bytestring. Cheers, Rinat

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ANN: hledger-1.14
by Simon Michael 02 Mar '19

02 Mar '19

I'm pleased to announce the release of hledger 1.14! Thank you release contributors Jakob Schöttl and Jakub Zárybnický. hledger is a robust, cross-platform plain text accounting tool, for tracking money, time, stocks, cryptocurrencies or any other commodity, using double-entry accounting, private or shared plain text files, revision control, and command-line, curses or web UIs. Find out more at http://hledger.org and http://plaintextaccounting.org. Release notes summary: ---------------------- Inclusive balance assertions, commodities command, --invert option, JSON get/add support in hledger-web. For full details, see http://hledger.org/release-notes. Getting started: ---------------- All install methods are described at http://hledger.org/download . (system packages, windows binaries, docker, nix, cabal, stack, hledger-install bash script..) Some of these might take a few days to become up to date. Tutorials and all docs and support options are linked at http://hledger.org . Get help via chat in #hledger on Freenode: http://irc.hledger.org Or connect via Matrix: http://riot.hledger.org New and old users, contributors, sponsors, positive/negative feedback, always welcome! Best, -Simon

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wiki-account-request
by Miguel 01 Mar '19

01 Mar '19

Hi, Not receiving any response from the other channel I hereby request a wiki.haskell.org account with the preferred username: "oo_miguel" Thanks in Advance, Michal Idziorek Ref: https://wiki.haskell.org/index.php?title=Special:UserLogin "If you would like an account please email 'wiki-account-request' (at the domain haskell dot org) or, if you find that unresponsive, on the haskell-cafe mailing list."

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show in monad
by Damien Mattei 01 Mar '19

01 Mar '19

just for tracing the monad i have this : import Control.Monad import Data.Ratio import Data.List (all) import Debug.Trace newtype Prob a = Prob { getProb :: [(a,Rational)] } deriving Show instance Functor Prob where fmap f (Prob xs) = trace " Functor Prob " Prob $ map (\(x,p) -> (f x,p)) xs t flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs instance Applicative Prob where pure = trace " Applicative Prob return " return (<*>) = trace " Applicative Prob ap " ap instance Monad Prob where return x = trace " Monad Prob return " Prob [(x,1%1)] m >>= f = trace " Monad Prob >>= " flatten (fmap f m) fail _ = trace " Monad Prob fail " Prob [] {- instance Applicative Prob where pure a = Prob [(a,1%1)] Prob fs <*> Prob as = Prob [(f a,x*y) | (f,x) <- fs, (a,y) <- as] instance Monad Prob where Prob as >>= f = Prob [(b,x*y) | (a,x) <- as, let Prob bs = f a, (b,y) <- bs] -} in this : flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs i have this error: [1 of 1] Compiling Main ( monade.hs, interpreted ) monade.hs:22:43: error: • No instance for (Show a) arising from a use of ‘show’ Possible fix: add (Show a) to the context of the type signature for: flatten :: forall a. Prob (Prob a) -> Prob a • In the second argument of ‘(++)’, namely ‘show xs’ In the first argument of ‘trace’, namely ‘(" flatten " ++ show xs)’ In the expression: trace (" flatten " ++ show xs) Prob | 22 | flatten (Prob xs) = trace (" flatten " ++ show xs) | ^^^^^^^ Failed, no modules loaded. how can i implement a show for xs ? regards, damien

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qtHaskell
by David Harley 28 Feb '19

28 Feb '19

I've made a new version of qtHaskell - version 1.1.10.1 available at the following site: http://www.isptech.co.uk/qtHaskell/download.html It comprises bindings to about 50 Qt modules and includes a version of Asteroids which uses functional reactive programming and some code running in a non-IO based monad, plus a Qt based version of Threadscope (qts). The installation of a code set of this sort can be tricky, it builds using a combination of cabal, qmake and make controled from perl. I wish it were simpler, but in most cases: ./build lite -jx will build all modules required for the demos and examples. It has currently only been tested on Linux hence, the build script which used to work on Windows will probably not work without some modification. I'll get around to that if there's any interest. It has also only been tested against regular builds of Qt 5.11/5.12 build from the qt-everywhere-src-5.11/12.x codesets. Good luck with any building and testing of qtHaskell-1.1.10.1, and I'd be delighted to get any feedback David Harley

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rounding and undefined behavior
by Matt Peddie 28 Feb '19

28 Feb '19

Hi cafe, It's been my general impression that when neither Haskell nor C defines behavior in a particular situation, the behavior nonetheless matches. I was surprised to observe Prelude Data.Int> round (4294967295 :: Double) :: Int16 -1 when #include <stdio.h> #include <inttypes.h> int main(void) { double d = 4294967295; int16_t r = (int16_t) d; printf("%"PRId16"\n", r); return 0; } yields 0 when compiled and run. As far as I can tell, neither language defines what this result should be, so neither is doing anything wrong here. But I was surprised that they differ; does anyone know why Haskell's rounding operation behaves the way it does (maybe there is some historical reason)? Or can someone perhaps point me to a standards document I missed that states how the language must round out-of-bounds inputs? Regards Matt Peddie

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