- Haskell-Cafe - Haskell.org

Unused Arrow commands do not give warning
by Tom Ellis 06 Nov '13

06 Nov '13

GHC can give you a warning when you fail to use the result of a monadic action in a do block. The same does not hold for arrow commands in arrow notation. (See demonstration below signature). What would it take to add a warning for this? I am writing arrow-heavy code at the moment and I think such a warning would be a nice feature. Tom % cat Test.hs {-# LANGUAGE Arrows #-} module Test where import Control.Arrow (returnA, arr) import Control.Monad.Identity (Identity(..)) foo :: Identity () foo = do Identity True return () bar :: () -> () bar = proc () -> do arr (const True) -< () returnA -< () % ghc -fforce-recomp -Wall Test.hs [1 of 1] Compiling Test ( Test.hs, Test.o ) Test.hs:10:5: Warning: A do-notation statement discarded a result of type Bool. Suppress this warning by saying "_ <- Data.Functor.Identity.Identity GHC.Types.True", or by using the flag -fno-warn-unused-do-bind

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Soostone Hiring In Turkey
by Ozgun Ataman 05 Nov '13

05 Nov '13

Dear Haskellers, Soostone is hiring Haskell programmers for its Turkey R&D group located in METU research park in Ankara. These position(s) are only available for local candidates with no possibility for remote work at this point in time. Interested fellow Haskellers may respond directly to me or to jobs(a)soostone.com. Soostone is an enterprise analytics company with a technology stack built entirely on Haskell. We work on interesting engineering challenges that span a multitude of topics in our area of expertise, including big-data crunching, predictive models, machine learning, data visualization and web-app development - all predominantly using Haskell. As a full-time member of our team in Ankara, you will work collaboratively with our HQ team in New York and get a chance to put your Haskell skills to use in real-world research, products and services. Soostone is also very involved with the open source community. Our team members maintain several packages on Hackage, contribute significantly to the Snap Web Framework, co-organize the New York Haskell Meetup and frequently participate in various community debates. We encourage all our team members to play an active role in the community in ways they find interesting and rewarding. Ideal candidates for this position will have: - A solid grasp of the Haskell language with an ability to produce working code from from day one (monad transformers, concurrency, streaming IO, dealing with space leaks, etc.) - Significant experience crafting software products, in academia and/or the industry - Strong presence in the OSS community with released packages in Hackage considered a big plus - Good communication skills and comfort in working as part of a team - Significant experience in a relevant application area such as compilers, distributed computing, numerics, machine learning, simulations or graphics - Experience in web application development and familiarity with web technologies - Willingness and enthusiasm to learn quickly and extend capabilities in new directions as necessary We look forward to hearing from interested candidates. The Soostone Team

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Cabal: --enable-shared and executables
by Magnus Therning 05 Nov '13

05 Nov '13

We've had a discussion about DSOs on the arch-haskell mailing list[1] and it made me realise one thing: --enable-shared will cause the generation of DSOs for libraries, but it won't cause executables to be dynamically linked Is the only way to cause these executables to be dynamically linked against their dependencies to pass the -dynamic flag to ghc (e.g. via the --ghc-options flag when configuring the package)? That then raises the issue of finding the DSOs. Something that is discussed in the Ghc documentation[2]. However, the generated DSOs are correctly linked to their dependencies. I guess what I'm trying to get to is that it seems to me that Cabal only provides half the solution to DSOs; it solves generation, but not usage. Is that an observation that people agree with? Are there any plans to solve this (maybe it's already solved in 1.18)? /M [1]: http://www.haskell.org/pipermail/arch-haskell/2013-October/004599.html [2]: http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/using-shared-libs.ht… -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus The day after tomorrow is the third day of the rest of your life.

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When will next release of haskell-platform come?
by yi lu 05 Nov '13

05 Nov '13

Hi, As the subject goes, when will it come? http://trac.haskell.org/haskell-platform/wiki/ReleaseTimetable Even though I hope for a `good` release to use, I hope to use it earlier. BTW, what are you expecting for this release? Best Regards, Yi

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updating multiple fields of a record with lenses
by felipe zapata 04 Nov '13

04 Nov '13

Dear Haskellers, let's suppose I have the following lenses data Foo = Foo { _a :: String _b :: [Double] _c :: Vector Double _d :: Int .............. (more fields) _z :: Double } Now, I want to update fields a,b,c and d without changing the rest. What is the functional way of doing it ? Surely there a function smarter than set a "String" . set b [1,2,3] . set c <1,2,3> . set d 4 $ foo can some please help me with it? Thanks in advance, Felipe Z.

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ANNOUNCE: Rlang-QQ 0.1
by adam vogt 04 Nov '13

04 Nov '13

Greetings, I'm pleased to announce a new version of Rlang-QQ. It is a way to get R code inline in you .hs files. The main highlight for this release is that correctly named variables assigned to in R are available to haskell. Many data types can be converted. You can get this package by cabal update && cabal install Rlang-QQ Please refer to the documentation here <http://hackage.haskell.org/package/Rlang-QQ-0.1.0.2> or in the examples/* that you can get at with a: cabal unpack Rlang-QQ Regards, Adam Vogt

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SSL support for hackage and cabal
by Eli Frey 04 Nov '13

04 Nov '13

Hello all, It recently came to my attention that hackage is http only. I would love to do anything I can to help hackage support https. What is the process for volunteering with the IHG (I imagine this is the avenue for helping with hackage/haskell.org) If the IHG is having dificulty getting an SSL certificate, GlobalSign (ful disclosure, they are my employer) provides free certificates to FOSS projects. here is a link: https://www.globalsign.com/ssl/ssl-open-source/ I am also concerned that cabal does not have support for SSL, but hackage must come first and at least then a sufficiently paranoid person can download their packages over https and ad them to their cabal sandboxes. Cheers, Eli

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How to avoid floods of fromIntegral (in ALSA.Sequencer)
by martin 04 Nov '13

04 Nov '13

Hello all, in my recent attempts to work with ALSA.Sequencer, I frequently stumble across the problem that this library uses GHC.Word.Word8 (don't know where this comes from), but I am passing in plain Ints. Adding a fromIntegral solves this issue, but I end up with code like the following: type T = Int -- time type C = Int -- channel type N = Int -- note type V = Int -- velocity type L = Int -- LSB type M = Int -- MSB type P = Int -- program type X = Int -- something data DtzEvent = NoteOn C N V | NoteOff C N V | ProgChange C P | PitchBend C X | BankSelMsb C X | BankSelLsb C X ... playSong :: DtzEvents -> IO() playSong events = runContT (foo "128:0" 120 (map render events)) print where render (t,(NoteOn c n v)) = ((fromIntegral t), noteOn (fromIntegral c) (fromIntegral n) (fromIntegral v)) render (t,(NoteOff c n v)) = ((fromIntegral t), noteOff (fromIntegral c) (fromIntegral n) (fromIntegral v)) render (t,(ProgChange c p)) = ((fromIntegral t), progChange (fromIntegral c) (fromIntegral p)) render (t,(PitchBend c x)) = ((fromIntegral t), pitchBend (fromIntegral c) (fromIntegral x)) render (t,(BankSelMsb c x)) = ((fromIntegral t), bankSelMsb (fromIntegral c) (fromIntegral x)) render (t,(BankSelLsb c x)) = ((fromIntegral t), bankSelLsb (fromIntegral c) (fromIntegral x)) The last piece looks pretty ugly. Is there a way to avoid this?

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Can't install vector-0.10.9.1 on OS X Maverick
by Alfredo Di Napoli 03 Nov '13

03 Nov '13

Hello Cafè, this is what I'm getting: ╰─$ cabal install vector-0.10.9.1 1 ↵ Resolving dependencies... Configuring vector-0.10.9.1... Building vector-0.10.9.1... Preprocessing library vector-0.10.9.1... [ 1 of 19] Compiling Data.Vector.Storable.Internal ( Data/Vector/Storable/Internal.hs, dist/build/Data/Vector/Storable/Internal.o ) [ 2 of 19] Compiling Data.Vector.Fusion.Util ( Data/Vector/Fusion/Util.hs, dist/build/Data/Vector/Fusion/Util.o ) [ 3 of 19] Compiling Data.Vector.Fusion.Stream.Size ( Data/Vector/Fusion/Stream/Size.hs, dist/build/Data/Vector/Fusion/Stream/Size.o ) Data/Vector/Fusion/Stream/Size.hs:25:10: Warning: No explicit method or default declaration for `*' In the instance declaration for `Num Size' Data/Vector/Fusion/Stream/Size.hs:25:10: Warning: No explicit method or default declaration for `abs' In the instance declaration for `Num Size' Data/Vector/Fusion/Stream/Size.hs:25:10: Warning: No explicit method or default declaration for `signum' In the instance declaration for `Num Size' [ 4 of 19] Compiling Data.Vector.Internal.Check ( Data/Vector/Internal/Check.hs, dist/build/Data/Vector/Internal/Check.o ) [ 5 of 19] Compiling Data.Vector.Fusion.Stream.Monadic ( Data/Vector/Fusion/Stream/Monadic.hs, dist/build/Data/Vector/Fusion/Stream/Monadic.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... <command line>: can't load .so/.DLL for: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/lib/libiconv.dylib (dlopen(/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/lib/libiconv.dylib, 9): no suitable image found. Did find: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/lib/libiconv.dylib: mach-o, but wrong filetype) Failed to install vector-0.10.9.1 cabal: Error: some packages failed to install: vector-0.10.9.1 failed during the building phase. The exception was: ExitFailure 1 I've did the trick of installing gcc-4.8 as described here: http://cp.reddit.com/r/haskell/comments/1ozukp/anyone_running_ghc_763_on_os… I'm running a compiled version of ghc 7.6.3 (so not installed via the Haskell platform). Have anyone stumbled upon this? Thanks, Alfredo

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more generic class instances?
by Christopher Howard 02 Nov '13

02 Nov '13

Hi. I am playing around with basic Haskell overloading. What I'm interested in is how to do specialization in Haskell -- i.e., functions that work generically on all (or many) types but work more efficiently on certain types. So, I am trying to make a class of functions which can be fed into a partial sum calculator. Maybe something like so: class PartialSum f where -- params: term function, end index partialSum :: Integral b => f -> b -> a The most generic instance would be any function that takes an integer and returns a number. The specialized instances would things like, say, a wrapped function which is guaranteed to be linear (through safe constructors or something). But I'm having trouble figuring out how even to make the generic version. I'm thinking something like this: instance PartialSum (a -> b) where partialSum f n = foldl (\u v -> u + f v) 0 [1..n] But the compiler complains it can't prove that the input to the "f" function is the same type as the "n" parameter. That makes sense, but I'm not sure how to fix that.

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