- Haskell-Cafe - Haskell.org

Haskell dev role in Strats at Standard Chartered (Singapore)
by Don Stewart 03 Jun '15

03 Jun '15

I have an open position for a Haskell developer to join Standard Chartered's Strats team in Singapore. More details at: https://donsbot.wordpress.com/2015/06/03/haskell-dev-role-in-strats-at-stan… -- Don

1 0

Blog platform written in Haskell
by Nicola Gigante 02 Jun '15

02 Jun '15

Hi all, Is there a blog platform written in Haskell? I mean something dynamic (as opposed to a static site generator like hakyll) like WordPress but written in Haskell. Does something like that exist? Greetings, Nicola

9 13

Four Designs for a Monad
by Zemyla 02 Jun '15

02 Jun '15

I'm working on writing a Haskell wrapper for the GNU Lightning code generation library (http://www.gnu.org/software/lightning/) which in C consists of a series of macros that write to a certain global state in a pointer _jit, such as jit_add or jit_call. Now, I figure that can be wrapped fairly simply in a monad, which we'll call the Lightning monad: -- syntax given here is just a sample. incr = lightningEmit $ do prolog in <- arg getArg R0, in addi R0, R0, 1 retr R0 However, I've come up with four possible designs for the Lightning monad. All but one would be reader monad transformers holding the pointer to the JIT state. 1) Lightning m a, where m is a MonadIO. Pros: Users have the power of the monads they are using within. Cons: Complexity, especially with having to handle monads with multiple returns like ListT. 2) Lightning a, which just wraps IO, and is a MonadIO. Pros: Allows the use of other IO functions in the monad. Cons: Allows the use of other IO functions in the monad. 3) Lightning a, which just wraps IO, and is not a MonadIO. Pros: Simplicity; possibly permitting the code generation to be unwrapped with unsafePerformIO. Cons: Referential integrity could still be violated. 4) Lightning a, which would be a free monad over the Lightning operations allowed. Pros: Evaluation (in the IO monad) would be certain to be pure, which would permit or accommodate it being a monad transformer, or converted to a pure function on architectures where the Lightning library is not available. Cons: Assembling, then disassembling to reassemble, a long list of instructions produces significant overhead, rendering it less suitable for JIT purposes. Interacting with the generated code is more difficult. Are there any other options I am missing? Are there any possibly game-changing pros or cons I have failed to notice? Thanks, Paul Drees

1 0

I think someone had a complicated program to use brackets for array indexing - is it possible to use a DSL for this?
by KC 02 Jun '15

02 Jun '15

I think someone had a complicated program to use brackets for array indexing - is it possible to use a DSL for this? That is, to use myArray [5] and have a DSL convert it to standard Haskell syntax -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

6 10

ANN: Bayhac 2015 June 12, 13, 14 in Mountain View, CA
by Byron Hale 02 Jun '15

02 Jun '15

Bayhac 2015 will be held June 12, 13, 14 at Hackers Dojo in Mountain View, CA. See http://bayhac.org/ to register. Light rail service is available from Caltrain to near Hackers Dojo. In addition, there can be shuttle service from Caltrain first thing in the morning and in the evening. Some known speakers are: Conal Elliott, Phil Freeman, Greg Weber, and Dan Burton You! If you would like to give a talk, send an email to bayhac2015-admin(a)googlegroups.com with the title and a brief explanation of what the talk will be on. It can be on anything Haskell related! We are also looking out for people who might be interested in conducting a more hands-on workshop. Twitter: https://twitter.com/bayhac2015 Byron Hale byron.hale(a)einfo.com @Hale_ByronL

1 0

ANN: toysolver 0.3.0 released
by Masahiro Sakai 01 Jun '15

01 Jun '15

Dear all, I'm announcing the release of the toysolver package. http://hackage.haskell.org/package/toysolver https://github.com/msakai/toysolver It provides solver implementations of various problems including SAT, Max-SAT, PBS (Pseudo Boolean Satisfaction), PBO (Pseudo Boolean Optimization), MILP (Mixed Integer Linear Programming) and non-linear real arithmetic. In particular it contains moderately-fast pure-Haskell SAT solver 'toysat'. It can also be used as a backend for ersatz and satchmo. http://hackage.haskell.org/package/ersatz-toysat http://hackage.haskell.org/package/satchmo-toysat Regards, -- Masahiro Sakai

2 1

A Dockerfile to provision a build environment for an Android game written in Haskell
by Sean Seefried 01 Jun '15

01 Jun '15

Fellow Haskell users! For the last few months I've been working on a small game targeting Android devices. It's still in development and will probably change radically from what I've already done. However, in the process of developing this game I've managed to develop a Dockerfile that will provision a build environment to build the game, which I think is worth releasing to the Haskell community right away. I'd appreciate some assistance in validating that it, in fact, works. The repo containing the Dockerfile is hosted at: https://github.com/sseefried/docker-epidemic-build-env The repo containing the game is: https://github.com/sseefried/open-epidemic-game Please use the latest version of Docker when you attempt to build this, at least version 1.6. Be aware that this will take a long time to build. You will need to download an image from THe Docker Hub Registry that is about 1.1G and then pull down even more files when building all the C and Haskell libraries. Be patient and if you have any issues please let me know via GitHub. Oh, and if you want to see a demo of what you are building click here: https://goo.gl/FZFPsm (It's a very simple game at present. Don't expect too much.) Enjoy! Sean

1 0

.a files not found
by Henk-Jan van Tuyl 30 May '15

30 May '15

L.S., I get messages about .a files not being found, when I try to install package data-default-instances-base, data-default-instances-containers, data-default-instances-dlist or data-default-instances-old-locale. How can I solve this? I am using GHC 7.10.1 on Windows. Sample output: C:\X\data-default-instances-old-locale-0.0.1> cabal install Resolving dependencies... Configuring data-default-instances-old-locale-0.0.1... Building data-default-instances-old-locale-0.0.1... Failed to install data-default-instances-old-locale-0.0.1 Build log ( C:\Users\X\AppData\Roaming\cabal\logs\data-default-instances-old-locale-0.0.1.log ): Building data-default-instances-old-locale-0.0.1... Preprocessing library data-default-instances-old-locale-0.0.1... [1 of 1] Compiling Data.Default.Instances.OldLocale ( Data\Default\Instances\OldLocale.hs, dist\build\Data\Default\Instances\OldLocale.o ) C:\Programs\Haskell\MinGHC-7.10.1\ghc-7.10.1\mingw\bin\ar.exe: dist\build\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a-2192\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a: No such file or directory cabal: Error: some packages failed to install: data-default-instances-old-locale-0.0.1 failed during the building phase. The exception was: ExitFailure 1 Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

5 7

foldt fix proposal (HaskellWiki)
by Michael V. Antosha 30 May '15

30 May '15

hi ALL, I think I've found a mistake in foldt implementation on the Fold page[1] of the HaskellWiki. foldt :: (a -> a -> a) -> a -> [a] -> a foldt f z [] = z foldt f z [x] = x -- mistake? -- foldt f z [x] = f x z -- fix proposal foldt f z xs = foldt f z (pairs f xs) pairs :: (a -> a -> a) -> [a] -> [a] pairs f (x:y:t) = f x y : pairs f t pairs f t = t Without the fix, foldt just ignores z value in all cases except for the case of empty input list. (Which is an inconsistent behaviour I suppose.) The Examples page[2] also needs corresponding fix. Is this mail list a right place to ask for the HaskellWiki page fix? Thanks! Michael. [1] Tree-like folds @ Fold @ HaskellWiki https://wiki.haskell.org/Fold#Tree-like_folds [2] Examples @ Fold @ HaskellWiki https://wiki.haskell.org/Fold#Examples -- Michael V. Antosha http://mivael.in.ua xmpp:m@mivael.in.ua (Jabber ID)

2 1

Why is vector sort slower than list sort?
by Holden Lee 30 May '15

30 May '15

>From places like http://programmers.stackexchange.com/questions/180417/fastest-haskell-libra… and http://stackoverflow.com/questions/3655329/how-does-one-sort-with-data-vect… I'm led to believe that sorting mutable vectors is faster than sorting lists. However, when running on my own computer, I'm seeing the opposite effect. What's wrong with what I'm doing, or am I misunderstanding something? What's the fastest way to sort? Here's the code: Sort0.hs (List version) import Control.Monad import System.Random import qualified Data.Vector as IV import qualified Data.Vector.Mutable as MV import qualified Data.Vector.Generic as V import qualified Data.Vector.Algorithms.Intro as VA import qualified Data.List as L randList :: IO [Int] randList = sequence $ replicate 1000000 (randomIO :: IO Int) main = do v <- randList print $ L.sort v Here's Sort1.hs import Control.Monad import System.Random import qualified Data.Vector as IV import qualified Data.Vector.Mutable as MV import qualified Data.Vector.Generic as V import qualified Data.Vector.Algorithms.Intro as VA randVector :: IO (MV.IOVector Int) randVector = do v <- MV.new 1000000 forM [0..999999] $ \x -> do r <- randomIO :: IO Int MV.write v x r return v main = do v <- randVector VA.sort v iv <- V.unsafeFreeze v :: IO (IV.Vector Int) print . V.toList $ iv I'm compiling and running as follows: ghc -prof -fprof-auto -rtsopts -o Sort0 Sort0.hs ./Sort0 +RTS -p -sstderr -K99999999 -RTS Here are the traces; the first one is Sort0.hs (list version) and takes ~11s while the other takes ~17s: Sat May 30 05:06 2015 Time and Allocation Profiling Report (Final) Sort0.exe +RTS -p -sstderr -K99999999 -RTS total time = *11.43 secs* (11434 ticks @ 1000 us, 1 processor) total alloc = 1,966,669,596 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc main Main 61.4 49.4 randList Main 38.6 50.6 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 41 0 0.0 0.0 100.0 100.0 CAF GHC.IO.Encoding.CodePage 69 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding 67 0 0.0 0.0 0.0 0.0 CAF System.CPUTime 59 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Handle.FD 58 0 0.0 0.0 0.0 0.0 CAF Data.Fixed 54 0 0.0 0.0 0.0 0.0 CAF Data.Time.Clock.POSIX 50 0 0.0 0.0 0.0 0.0 CAF System.Random 49 0 0.0 0.0 0.0 0.0 CAF Main 48 0 0.0 0.0 100.0 100.0 randList Main 83 1 1.7 3.1 1.7 3.1 main Main 82 1 61.4 49.4 98.3 96.9 randList Main 84 0 36.9 47.6 36.9 47.6 Sat May 30 04:59 2015 Time and Allocation Profiling Report (Final) Sort1.exe +RTS -p -sstderr -K99999999 -RTS total time = * 17.07 secs* (17066 ticks @ 1000 us, 1 processor) total alloc = 5,783,472,528 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc main Main 71.9 81.5 randVector.\ Main 25.0 16.5 randVector Main 3.1 2.0 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 60 0 0.0 0.0 100.0 100.0 CAF GHC.IO.Encoding.CodePage 108 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding 106 0 0.0 0.0 0.0 0.0 CAF System.CPUTime 98 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Handle.FD 95 0 0.0 0.0 0.0 0.0 CAF Data.Fixed 87 0 0.0 0.0 0.0 0.0 CAF Data.Time.Clock.POSIX 82 0 0.0 0.0 0.0 0.0 CAF System.Random 81 0 0.0 0.0 0.0 0.0 CAF Main 67 0 0.0 0.0 100.0 100.0 randVector Main 121 1 0.0 0.0 0.0 0.0 main Main 120 1 71.9 81.5 100.0 100.0 randVector Main 122 0 3.1 2.0 28.1 18.5 randVector.\ Main 123 1000000 25.0 16.5 25.0 16.5 Thanks, Holden

2 1