November 2013 - Haskell-Cafe

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

1 0

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

14 25

How to avoid floods of fromIntegral (in ALSA.Sequencer)
by martin 03 Nov '13

03 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?

4 4

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

2 9

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.

2 5

LiberalTypeSynonyms: documentation issue
by Obscaenvs 02 Nov '13

02 Nov '13

In the docs for GHC 7.6.3, e.g. at [1], it is said that one can use LiberalTypeSynonyms as so: `type Discard a = forall b. Show b => a -> b -> (a, String)` This is, however, not possible without RankNTypes which is stated in a tutorial at FPComplete [2] and, of course, GHC 7.6.3 itself says so when trying to compile something with the above definition for Discard: ` Illegal polymorphic or qualified type: forall b. Show b => a -> b -> (a, String) Perhaps you intended to use -XRankNTypes or -XRank2Types In the type declaration for `Discard' ` Maybe the GHC User Guide should be updated to reflect this? /Fredrik References: [1] http://www.bugthunk.net/ghc/docs/7.6.3/html/users_guide_repl/data-type-exte… [2] https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/g…

1 0

beginners list for common lisp?
by Christopher Howard 02 Nov '13

02 Nov '13

Does anybody know if there is something like a Common Lisp version of the Haskell Beginner's mailing list? Haskell's great, of course, but I've also been picking up Lisp, and I'm looking for a Lisp list that is very newbie friendly.

3 2

Re: [Haskell-cafe] Cabal sandboxes over cabal-dev (Rogan Creswick)
by Gregory Guthrie 01 Nov '13

01 Nov '13

"I *strongly* suggest everyone start transitioning from cabal-dev to cabal sandboxes." Is there any reason that this is not just the default install mode for Cabal? Anything that prevents the current cabal-swamp of broken dependencies is a great help. I have tried to use Haskell in some classes, but it is hard when students (and I) cannot install packages, and the only answer is the Microsoft-like; "delete everything and start over; reinstall". It certainly reduces their confidence that Haskell is a feasible working environment.

11 18

ANNOUNCE: HList-0.3
by adam vogt 01 Nov '13

01 Nov '13

Greetings, We are pleased to announce HList-0.3. This is an update the well-known library for strongly typed heterogenous lists, records, type-indexed products (TIP) and co-products. Some of the highlights are: * works with lens. See examples/labelable.hs * modern features such as TypeFamilies, DataKinds (Symbol), ConstraintKinds, PolyKinds, QuasiQuotes * Data instances for HList and Record. One application is given in examples/cmdargs.hs * named and optional function parameters (using Keyword or perhaps RecordPuns) are part of the library proper * additional functions including: HTranspose, HZip, HFoldl, HScanr, HReplicate * improved type inference. To give an example: > let y = hMap (Fun' read :: Fun' Read String) x This is about the same as `let y = map read x', but each element of the HList `y' can have a different type. Only one of the two lengths needs to be specified. * more documentation and examples, which should make it easier to find your way around. Refer to the included ChangeLog or `darcs changes` for more details. This release requires ghc>=7.6. You can get the release from <http://hackage.haskell.org/package/HList> or use cabal-install: $ cabal update $ cabal install HList-0.3 For now it seems that hackage is rejecting the upload due to language extensions it doesn't know about, so in the meantime you can get it with: $ cabal install http://code.haskell.org/~aavogt/HList/HList-0.3.0.tar.gz With haddocks at <http://code.haskell.org/~aavogt/HList/docs/HList/>. -- Adam

1 0

How do I lift Control.Monad.Reader.local?
by David Fox 01 Nov '13

01 Nov '13

I can write a stack push function in the reader monad like so: import Control.Monad.Reader push :: String -> Reader [String] a -> Reader [String] a push s action = local (s :) action How can I write a push that works inside a monad transformer? push' :: MonadTrans t => String -> t (Reader [String]) a -> t (Reader [String]) a push' s action = ???

2 4