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Making the encoding Haskell package compile with ghc-7.8.2
by José Romildo Malaquias 20 May '14

20 May '14

Hello. I use encodign in a Haskell application and I would like to have it working with ghc-7.8.2. So I am kindly asking to, if possible, update the encoding package[1] to be compilable with ghc-7.8.2. Currently it fails with the messages: [...] * Prepending /usr/lib64/ghc-7.8.2 to LD_LIBRARY_PATH /usr/bin/ghc -package Cabal-1.20.0.0 --make /tmp/portage/dev-haskell/encoding-0.7/work/encoding-0.7/Setup.hs -dynamic -o setup [1 of 8] Compiling Data.Static ( Data/Static.hs, Data/Static.o ) Data/Static.hs:39:28: Couldn't match expected type ‘Bool’ with actual type ‘Int#’ In the expression: eqWord# v (int2Word# 4294967295#) In the expression: if eqWord# v (int2Word# 4294967295#) then Nothing else (if (I# (word2Int# v)) > 1114111 then error (show (I# (word2Int# v)) ++ " is not a valid char (" ++ show (I# i) ++ ")") else Just (chr (I# (word2Int# v)))) /usr/bin/ghc -package Cabal-1.20.0.0 --make /tmp/portage/dev-haskell/encoding-0.7/work/encoding-0.7/Setup.hs -o setup [1 of 8] Compiling Data.Static ( Data/Static.hs, Data/Static.o ) Data/Static.hs:39:28: Couldn't match expected type ‘Bool’ with actual type ‘Int#’ In the expression: eqWord# v (int2Word# 4294967295#) In the expression: if eqWord# v (int2Word# 4294967295#) then Nothing else (if (I# (word2Int# v)) > 1114111 then error (show (I# (word2Int# v)) ++ " is not a valid char (" ++ show (I# i) ++ ")") else Just (chr (I# (word2Int# v)))) Regards, Romildo

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ANNOUNCE: New OpenGL packages
by Sven Panne 19 May '14

19 May '14

New versions of the OpenGL packages are available on Hackage: * OpenGLRaw 1.5.0.0 * GLURaw 1.4.0.1 * OpenGL 2.9.2.0 * GLUT 2.5.1.1 Cheers, S. ====================================================================== Changes in the OpenGLRaw package ====================================================================== * Don't rely on K&R features in CPP, making things easier for Mac/clang users. * Added support for OpenGL 3.2's glGetInteger64i_v and the following extensions, so now all parts of OpenGL 4.1 are supported (plus a few more): APPLE_flush_buffer_range APPLE_vertex_array_object ARB_blend_func_extended ARB_gpu_shader_fp64 ARB_sampler_objects ARB_shader_subroutine ARB_shading_language_include ARB_texture_compression_bptc ARB_texture_rgb10_a2ui ARB_texture_swizzle ARB_transform_feedback2 ARB_vertex_attrib_64bit ARB_vertex_type_2_10_10_10_rev EXT_draw_buffers2 EXT_framebuffer_blit EXT_framebuffer_multisample EXT_gpu_shader4 EXT_packed_stencil_depth EXT_texture_array EXT_texture_compression_rgtc EXT_texture_shared_exponent EXT_transform_feedback * Made naming more consistent: Abgr => ABGR Bgra => BGRA Cmyka => CMYKA Dxt1 => DXT1 Fp => FP Gpu => GPU Latc => LATC Lod => LOD S3tc => S3TC Vtc => VTC ====================================================================== Changes in the GLURaw package ====================================================================== * Don't rely on K&R features in CPP, making things easier for Mac/clang users. ====================================================================== OpenGL 2.9.2.0 ====================================================================== * Added generateMipmap’, a modern version of the deprecated generateMipmap. * Added a few missing IndexedBufferTargets. * indexedBufferSize and indexedBufferStart correctly use 64bit queries now. * Setting bindBufferRange handles Nothing correctly now. * Added missing Eq/Ord/Show instances for a few data types. ====================================================================== Changes in the GLUT package ====================================================================== * Don't rely on K&R features in CPP, making things easier for Mac/clang users. * Added ColorTriange example.

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Haskell Developer - Job Opening - New York, NY
by Ryan Trinkle 19 May '14

19 May '14

skedge.me is seeking a Haskell developer to improve and maintain our Snap-based web application stack. skedge.me is committed to using the best tool for the job throughout our software stack. That includes a mixture of cutting-edge tools like Haskell and the Nix package manager as well as tried-and-true products like PostgreSQL and Linux. Your role will be to find, use, and create tools like these to build a robust and powerful software platform to serve our clients' needs. This job requires that you be able to hit the ground running with Haskell. As part of your application, please submit a small to medium sized code sample (approximately 100 to 1000 lines) demonstrating your ability to write clear, concise, and efficient Haskell code, together with a brief English explanation of what the code does, how it works, and how to build and run it. Your Haskell code is our primary consideration in reviewing your application. However, experience with PostgreSQL, Linux, NixOS, web server programming, Varnish, AWS or other similar technologies is a plus. It is also a plus if you are local to the NYC area, as our offices are located in Midtown. To apply, please email me your resume and code sample at ryan(a)skedge.me. Ryan

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Constants in Class definitions - could not deduce
by martin 18 May '14

18 May '14

Hello all, in my attempt to solve a Calendar related problem, I wanted to define Months and Weekdays such that I can increment a value. Unlike the "succ" Funktion in Enum my "inc" function shall circle endlessly. I came up with the following class (Ix a, Enum a) => Incrementable a where from :: a to :: a inc :: a -> a inc x = [from .. to] !! ((1 + index (from, to) x) `mod` rangeSize (from,to)) but GHC complains: /home/martin/projects/haskell/euler/p19.hs:39:65: Could not deduce (Ix a0) arising from a use of `rangeSize' from the context (Incrementable a) I suppose this is because GHC does not know that I want "to" and "from" to be taken from the same instance as x. If I replace the signature of "from" by "a -> a" and implement it by using a function which throws aways its argument, the types become clear and GHC no longer complains. Alternatively I can omit the implementation of "inc" in the class and leave that to the instances. I can easily fix the types in the instances, but this leads to some code duplication. I tried (from::a) to fix the type, but this had no effect. How is this done correctly?

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Conduits vs. lazy byte strings
by Mike Meyer 18 May '14

18 May '14

I'm working on a web app that loads a file, tweaks it a bit, then downloads the results. I'd like for it to use the minimal amount of memory possible, just as good practice. Especially since the tweaking all happens in the first K or so of the file, and the rest of it is passed through untouched. The current version uses a conduit that just reads the data to a sinkLbs to get a lazy bytestring, which is then processed. I think this will have the desired behavior (after all, the bytestring is lazy), but have this itch that says I should be doing the processing in the conduit. Someone want to tell me if I correctly understand things and the itch is just leftover imperative thinking, or the itch is right and I need to fix the code? If you're intersted, you can find the code at https://www.fpcomplete.com/user/mwm/xyzifiy

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Packaging Haskell Environment for Mac App
by Andrew Gibiansky 18 May '14

18 May '14

Hey all, [This is an xpost from Reddit, where the post<http://www.reddit.com/r/haskell/comments/24hct1/packaging_haskell_platform_…>seems not to be showing up for some reason...] I'd like to package the Haskell Platform and GHC (for GHC API) together in one bundle in order to distribute it with a Mac app. (Specifically, I am working on a Mac app for IHaskell <https://github.com/gibiansky/IHaskell>, so beginners can download that to immediately get started playing with Haskell). Does anyone have any experience with this? What's the easiest way to do this? My list of dependencies is fairly long: - Haskell Platform (well, all packages in it) - A few other packages installed via cabal - A native library (libzmq); cabal packages depend on it - Functioning Python > 2.6ish - GHC API My current best idea is to package this all in a Virtualbox VM. I need to run a server that my Mac app client can use, so mount shared folders in the VM so that the VM can read/write to disk and expose some ports from the VM. If this is the best solution, what Linux distro would you suggest to use in the VM? I'd want something very lightweight. I've also considered using Docker somehow, as IHaskell is already packaged with a Dockerfile. However, I'm not sure how I'd package docker so that its all doable via a single Mac app install. Ideas? Suggestions? Thanks! I know this isn't *directly* related to Haskell, but I'm hoping someone here has experience packaging Haskell applications. -- Andrew Gibiansky

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System.Process and -threaded
by Karsten Gebbert 18 May '14

18 May '14

Hello, I'm writing a little networking wrapper around a sub-process (mplayer -idle -slave) and I'm running into some issues with the System.Process API. This is the program: > module Main where > > import System.IO > import System.Process > import Network.Socket hiding (recv) > import Network.Socket.ByteString > import Control.Concurrent > import qualified Data.ByteString.Char8 as C > > -- WARNING: when compiled with -threaded, this program is likely not going > -- to work. As soon as one writes to the stdin of the forked process, it > -- zombifies and any other command with crash this program. > > main = withSocketsDo $ do > -- network stuff > addrinfos <- getAddrInfo Nothing (Just "localhost") (Just "4000") > let serveraddr = head addrinfos > sock <- socket (addrFamily serveraddr) Stream defaultProtocol > bindSocket sock (addrAddress serveraddr) > listen sock 1 > > -- mplayer > (hand,o,e,pid) <- runInteractiveProcess "mplayer" ["-fs", "-idle", "-slave"] Nothing Nothing > hSetBinaryMode hand False > hSetBuffering hand LineBuffering > > putStrLn "listening for commands" > loop sock hand > > -- closing everything down > sClose sock > terminateProcess pid > waitForProcess pid > return () > > loop sock hand = do > (conn, _) <- accept sock > str <- recv conn 2048 > > putStr $ "received: " ++ C.unpack str > > -- write command to handler > hPutStr hand $ C.unpack str > > sClose conn > loop sock hand When compile with -threaded, the mplayer process gets zombified and hangs until I shut down the program. When compiled with non-threaded RTS (thats whats its called, correct?) I can successfully send a few commands, but then mplayer freezes. When I strace mplayer, this error is what it gets stuck on. ioctl(0, TIOCGWINSZ, 0x7fff2897a070) = -1 ENOTTY (Inappropriate ioctl for device) Apparently that means I'm trying to communicate with it as though it were a type writer. How fitting :) The commands are all simple strings as docs here: http://www.mplayerhq.hu/DOCS/tech/slave.txt My questions are these: is there anything I need to take care of when handling sub-processes like this, specifically while writing to stdin of the process, and with particular regard to -threaded? Does anybody spot a problem or something I'm overlooking when handling processes like this? I have been reading the API docs, but found no mention of potential caveats pertaining to -threaded. Thanks! k ✉ k(a)ioctl.it ☎ +49(0)176 / 61995110

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Status of efl-haskell?
by José Romildo Malaquias 18 May '14

18 May '14

Hello. I am interested in the project efl-haskell[1] a Haskell library that provides an interface to EFL (Enlightenment Foundation Libraries) and elementary (widget toolkit)[2]. The git repository[3] has seen almost no activity. It has been created and populated on Dec 2012 and has just a workaround update on Jan 2013. Is the project still being developed? [1] https://bitbucket.org/arrowdodger/efl-haskell [2] http://enlightenment.org/ [3] https://bitbucket.org/arrowdodger/efl-haskell Romildo

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Was directed here for help with why ghc is failing to find mtl.
by Haskell Beginner 17 May '14

17 May '14

This is the error message which started it all off: http://lpaste.net/104242 Then the following conversation happened: ============================================================================== --- JPMoresmau ------ First package to fail is exceptions. Just open a console and type in cabal install exceptions EclipseFP tries to put some parallel install flags that may make the errors less visible (a Cabal thing, not an EclipseFP thing). I really don't like the look of getting warnings in c code, though... --- haskell_beginner ------ $ cabal install exceptions Resolving dependencies... Configuring exceptions-0.6.1... /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/5187.c:1:12: warning: control reaches end of non-void function [-Wreturn-type] int foo() {} ^ 1 warning generated. Building exceptions-0.6.1... Preprocessing library exceptions-0.6.1... <command line>: cannot satisfy -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 (use -v for more information) Failed to install exceptions-0.6.1 cabal: Error: some packages failed to install: exceptions-0.6.1 failed during the building phase. The exception was: ExitFailure 1 $ What flags can I add to that to get a better error message? EDIT TO ADD: Again if there is another layer automatically adding flags to the above command, I know nothing about it. This includes if Haskell or cabal uses a config file. I am on a — to my knowledge — completely stock install of Haskell for Mac OS. --- JPMoresmau ------ cabal install -v exceptions May give more info about why the mtl package cannot be satisfied when it seems to have been installed. --- haskell_beginner ------ $ cabal install -v exceptions Reading available packages... Choosing modular solver. Resolving dependencies... Ready to install exceptions-0.6.1 Waiting for install task to finish... Extracting /Users/person/Library/Haskell/repo-cache/ hackage.haskell.org/exceptions/0.6.1/exceptions-0.6.1.tar.gz to /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/exceptions-0.6.1-5256... Updating exceptions.cabal with the latest revision from the index. Configuring exceptions-0.6.1... Dependency base ==4.6.0.1: using base-4.6.0.1 Dependency mtl ==2.1.2: using mtl-2.1.2 Dependency transformers ==0.3.0.0: using transformers-0.3.0.0 /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/5256.c:1:12: warning: control reaches end of non-void function [-Wreturn-type] int foo() {} ^ 1 warning generated. Using Cabal-1.16.0 compiled by ghc-7.6 Using compiler: ghc-7.6.3 Using install prefix: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1 Binaries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/bin Libraries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/lib Private binaries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/libexec Data files installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/share Documentation installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/doc Using alex version 3.0.5 found on system at: /usr/bin/alex Using ar found on system at: /usr/bin/ar No c2hs found Using cpphs version 1.18.1 found on system at: /Users/person/Library/Haskell/bin/cpphs No ffihugs found Using gcc version 4.2.1 found on system at: /usr/bin/gcc Using ghc version 7.6.3 found on system at: /usr/bin/ghc Using ghc-pkg version 7.6.3 found on system at: /usr/bin/ghc-pkg No greencard found Using haddock version 2.13.2 found on system at: /usr/bin/haddock Using happy version 1.18.10 found on system at: /usr/bin/happy No hmake found Using hpc version 0.6 found on system at: /usr/bin/hpc Using hsc2hs version 0.67 found on system at: /usr/bin/hsc2hs Using hscolour version 1.20 found on system at: /Users/person/Library/Haskell/bin/HsColour No hugs found No jhc found Using ld found on system at: /usr/bin/ld No lhc found No lhc-pkg found No nhc98 found No pkg-config found Using ranlib found on system at: /usr/bin/ranlib Using strip found on system at: /usr/bin/strip Using tar found on system at: /usr/bin/tar No uhc found creating dist/build creating dist/build/autogen Building exceptions-0.6.1... Preprocessing library exceptions-0.6.1... Building library... creating dist/build /usr/bin/ghc --make -fbuilding-cabal-package -O -odir dist/build -hidir dist/build -stubdir dist/build -i -idist/build -isrc -idist/build/autogen -Idist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -package-name exceptions-0.6.1 -hide-all-packages -package-db dist/package.conf.inplace -package-id base-4.6.0.1-6c351d70a24d3e96f315cba68f3acf57 -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 -package-id transformers-0.3.0.0-ff2bb6ac67241ebb987351a3db564af0 -XHaskell98 Control.Monad.Catch Control.Monad.Catch.Pure -Wall -fwarn-tabs -O2 <command line>: cannot satisfy -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 (use -v for more information) Failed to install exceptions-0.6.1 World file is already up to date. cabal: Error: some packages failed to install: exceptions-0.6.1 failed during the building phase. The exception was: ExitFailure 1 $ Hope that helps. I don't know what to make of it. :-/ --- JPMoresmau ------ Neither do I! It seems cabal finds a mtl package to use, but when it passes the exact reference of the package (with a trailing hash to indicate the specifics of your install), ghc doesn't find it. At least it's nothing to do with EclipseFP, which is a relief (for me :-p). I suggest you post that to the Haskell-Cafe mailing list if nobody has any clue here. I know that MacOS is a bit weird sometimes with PATH and such. ============================================================================== Thus with the history of this error now told (TL;DR: read JPMoresmau's last comment above), the question I pose to this mailing list is: Why is ghc failing to find mtl? Thanks, ~Haskell Beginner

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Research position "Coalgebraic Logic Programming for Type Inference"
by Ekaterina Komendantskaya 17 May '14

17 May '14

We have a fixed-term position at the School of Computing, Dundee for a postdoctoral researcher to work on the project Coalgebraic Logic Programming for Type Inference: a new generation of languages for parallelism and corecursion. More details are available below and at http://staff.computing.dundee.ac.uk/katya/CoALP/ For further inquiries please email me: Katya Komendantskaya <katya(a)computing.dundee.ac.uk> School of Computing University of Dundee Postdoctoral Researcher in Coalgebraic Logic Programming for Type Inference Fixed-term position for 2 years (extension possible). Start date: between 1 July 2014 and 1 October 2014; Salary scale: between £29,837 and £33,5562 per annum. Closing Date for applications: 16 June 2014. The School of Computing at the University of Dundee invites applications for a postdoctoral researcher to work on an interdisciplinary project "Coalgebraic Logic Programming for type inference: a new generation of languages for parallelism and corecursion" ( http://staff.computing.dundee.ac.uk/katya/CoALP/) The project spans several subjects, among which are: - -- Computational Logic, - -- (Coalgebraic) Operational semantics, - -- Functional Programming; - -- Logic Programming, - -- Recursion and Corecursion in Programming languages; -- Category Theory, - -- Type Theory; - -- Compilers - -- Parallelism and Concurrency The project is jointly led by Dr E.Komendantskaya, University of Dundee and Dr J.Power, University of Bath. We are looking for a researcher to spend up to 29 months in the Dundee team developing CoALP-based type inference. This will involve close collaboration with the existing group members, as well as interaction with the project partners. Research experience of at least a PhD level in computer science or mathematics is essential, as is some knowledge of either functional programming or automated/interactive theorem provers. ************************************** Project description: The main goal of typing is to prevent the occurrence of execution errors during the running of a program. Milner formalised the idea, showing that ``well-typed programs cannot go wrong''. In practice, type structures provide a fundamental technique of reducing programmer errors. At their strongest, they cover most of the properties of interest to the verification community. A major trend in the development of functional languages is improvement in expressiveness of the underlying type system, e.g., in terms of Dependent Types, Type Classes, Generalised Algebraic Types (GADTs), Dependent Type Classes and Canonical Structures. Milner-style decidable type inference does not always suffice for such extensions (e.g. the principal type may no longer exist), and deciding well-typedness sometimes requires computation additional to compile-time type inference. Implementations of new type inference algorithms include a variety of first-order decision procedures, notably Unification and Logic Programming (LP), Constraint LP, LP embedded into interactive tactics (Coq's eauto), and LP supplemented by rewriting. A second major trend is parallelism: the absence of side-effects makes it easy to evaluate sub-expressions in parallel. Powerful abstraction mechanisms of function composition and higher-order functions play important roles in parallelisation. Three major parallel languages are Eden (explicit parallelism), Parallel ML (implicit parallelism) and Glasgow parallel Haskell (semi-explicit parallelism). Control parallelism in particular distinguishes functional languages. Type inference becomes more sophisticated and takes a bigger role in the overall program development. In this project, we have devloped a new dialect of logic programming -- Coalgebraic Logic Programming (CoALP) that features both extra expressiveness (via corecursion) and parallelism in one algorithm. We propose to use CoALP in place of LP tools currently used in type inference. With the mentioned major developments in Corecursion, Parallelism, and Typeful (functional) programming it has become vital for these disjoint communities to combine their efforts: enriched type theories rely more and more on the new generation of LP languages; coalgebraic semantics has become influential in language design; and parallel dialects of languages have huge potential in applying common techniques across the FP/LP programming paradigm. This project is unique in bringing together local and international collaborators working in the three communities. See http://staff.computing.dundee.ac.uk/katya/CoALP/ for more details. *************************************************************** Ekaterina Komendantskaya Senior Lecturer, Head of PhD Studies Room 1.04, Queen Mother Building School of Computing, University of Dundee Scotland, DD14HN Tel: (+44) 01382384820

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