March 2012 - Haskell-Cafe

What happened with goa package repo?
by Dmitry Malikov 26 Mar '12

26 Mar '12

Cloning into bare repository '/usr/portage/distfiles/egit-src/goa.git'... fatal: The remote end hung up unexpectedly * ERROR: dev-haskell/goa-9999 failed (unpack phase): * git-2_initial_clone: can't fetch from git://github.com/chrisdone/goa.git https://github.com/chrisdone/goa returns 404. So it seems like Chris dropped that repo. Did someone have clone of it? It will be nice to put it back on github.

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Google Summer of Code: a NUMA wishlist!
by Sajith T S 25 Mar '12

25 Mar '12

Dear Cafe, It's last minute-ish to bring this up (in my part of the world it's still March 25), but graduate students are famously a busy and lazy lot. :) I study at Indiana University Bloomington, and I wish to propose^W rush in this proposal and solicit feedback, mentors, etc while I can. Since student application deadline is April 6, I figure we can beat this into a real proposal's shape by then. This probably also falls on the naive and ambitious side of things, and I might not even know what I'm talking about, but let's see! That's the idea of proposal, yes? Broadly, idea is to improve support for NUMA systems. Specifically: -- Real physical processor affinity with forkOn [1]. Can we fire all CPUs if we want to? (Currently, the number passed to forkOn is interpreted as number modulo the value returned by getNumCapabilities [2]). -- Also kind of associated with the above: when launching processes, we might want to specify a list of CPUs rather than the number of CPUs. Say, a -N [0,1,3] flag rather than -N 3 flag. This shall enable us to gawk at real pretty htop [3] output. -- From a very recent discussion on parallel-haskell [4], we learn that RTS' NUMA support could be improved. The hypothesis is that allocating nurseries per Capability might be a better plan than using global pool. We might borrow/steal ideas from hwloc [5] for this. -- Finally, a logging/monitoring infrastructure to verify assumptions and determine if/how local work stays. (I would like to acknowledge my fellow conspirators and leave them unnamed, lest they shall be embarrassed by my... naivete.) Thanks, Sajith. [1] http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurre… [2] http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurre… [3] http://htop.sourceforge.net/ [4] http://groups.google.com/group/parallel-haskell/browse_thread/thread/7ec1eb… [5] http://www.open-mpi.org/projects/hwloc/ -- "the lyf so short, the craft so long to lerne." -- Chaucer.

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How to handle C library dependencies on Hackage?
by . 25 Mar '12

25 Mar '12

Hello Cafe, I recently did my first upload to Hackage: <http://hackage.haskell.org/package/jalla>. The library does not build (and therefore unfortunately the documentation is not built either), because the C library that it needs to wrap is usually not installed with normal Linux distributions. It's LAPACKE (note the E at the end). I /could/ upload the source code of that library alongside my Haskell library and build it using Setup.hs (this works on my computer). However, LAPACKE is large compated to my own library (about 16MB sources) and I don't want to flood Hackage with it if it's not necessary. Can anyone here give me some advice on how to solve this on the system that builds the hackage packages? Thanks very much, Christian

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Re: [Haskell-cafe] Open-source projects for beginning Haskell students?
by John Lato 25 Mar '12

25 Mar '12

> From: Heinrich Apfelmus <apfelmus(a)quantentunnel.de> > > Tom Murphy wrote: >> If you want to do Haskell audio synthesis, you could also use >> hsc3 (good start here: http://slavepianos.org/rd/ut/hsc3-texts/) With >> hsc3 you can start on serious audio synthesis with only a few lines of >> Haskell. In my opinion it could use a much larger community. > > While Rohan's bindings to SuperCollider are great, I have found that > SuperCollider itself is quite difficult to understand for a new user. > (My tomata-rubato project aims to be much easier to learn.) > > Also, as far as I am aware, you can't do low-level audio programming in > SuperCollider, i.e. play a list of samples that you've calculated > yourself. That's cool if you're only interested in sound design, but bad > for learning how audio programming works. I think this charge is a bit unfair. If you really want to do low-level stuff, it's possible within SC. You just have to work in SuperCollider, not Haskell (AFAIK). However, it is possible to transfer audio data between Haskell and Csound, in several ways. The hCsound package comes with some examples of transferring the audio input and output streams between csound and haskell. Named channels provide for even more complicated routing if you like. John L.

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GSoC project ideas for web technology
by Jeremy Shaw 25 Mar '12

25 Mar '12

Hello, If you are looking for some ideas for a GSoC project, I have written down some web technology related projects I would like to see. So far I mostly have ideas for improvements to HSX (a templating solution) and acid-state (a pure, haskell persistent datastore). Both these technologies can be used with any Haskell web framework (though they are embraced most fully by Happstack). http://code.google.com/p/happstack/wiki/GoogleSummerOfCode I am an officially registered Haskell GSoC mentor. I am happy to help expand any of these ideas into a genuine GSoC proposal and to act as a mentor on the project. If you have other ideas you wish to pitch, I am happy to hear those as well. - jeremy

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sinkfork using conduit 3.0
by grant 24 Mar '12

24 Mar '12

I am trying to update sinkfork to use conduits 3.0. The difficulty I am having is trying to figure out how to push a value into a SinkM constructor. Any ideas? Here is the old! conduits code 2.0: https://gist.github.com/1975383 Thanks in advance. Grant

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Alex character sets
by Omari Norman 24 Mar '12

24 Mar '12

I'm wrinting (or at least, trying to write) an Alex lexer. Say I want to group character ranges together and specify that I want a character that is *not* in any of those ranges. Example --- { module Main where } %wrapper "posn-bytestring" $lowAscii = \x00-\x1f -- unprintable stuff $lowSymbol = \x21-\x2f -- exclamation point to solidus $space = \x20 $special = [^$lowAscii $lowSymbol] lex :- $special { Word } { data Token = Word AlexPosn ByteString.ByteString } When I run this through Alex, I get "Prelude.Enum.Char.pred: bad argument". What am I doing wrong? How would I accomplish this sort of thing? Thanks. --Omari

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ANNOUNCE: options, an easy-to-use command-line option parser
by John Millikin 24 Mar '12

24 Mar '12

Hackage: http://hackage.haskell.org/package/options Home page: https://john-millikin.com/software/haskell-options/ API reference: https://john-millikin.com/software/haskell-options/reference/haskell-option… The options package lets library and application developers easily work with command-line options. The following example is a full program that can accept two options, --message and --quiet: ---------------------------------------------------------- {-# LANGUAGE TemplateHaskell #-} import Options defineOptions "MainOptions" $ do stringOption "optMessage" "message" "Hello world!" "A message to show the user." boolOption "optQuiet" "quiet" False "Whether to be quiet." main :: IO () main = runCommand $ \opts args -> do if optQuiet opts then return () else putStrLn (optMessage opts) ---------------------------------------------------------- ---------------------------------------------------------- $ ./hello Hello world! $ ./hello --message='ciao mondo' ciao mondo $ ./hello --quiet $ ---------------------------------------------------------- In addition, this library will automatically create documentation options such as --help and --help-all: ---------------------------------------------------------- $ ./hello --help Help Options: -h, --help Show option summary. --help-all Show all help options. Application Options: --message A message to show the user. --quiet Whether to be quiet. ----------------------------------------------------------

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Un-memoization
by Victor Miller 23 Mar '12

23 Mar '12

I was writing a Haskell program which builds a large labeled binary tree and then does some processing of it, which is fold-like. In the actual application that I have in mind the tree will be *huge*. If the whole tree is kept in memory it would probably take up 100's of gigabytes. Because of the pattern of processing the tree, it occurred to me that it might be better (cause much less paging) if some large subtrees could be replaced by thunks which can either recalculate the subtree as needed, or write out the subtree, get rid of the references to it (so it can be garbage collected) and then read back in (perhaps in pieces) as needed. This could be fairly cleanly expressed monadically. So does anyone know if someone has created something like this? Victor

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Open-source projects for beginning Haskell students?
by Brent Yorgey 23 Mar '12

23 Mar '12

Hi everyone, I am currently teaching a half-credit introductory Haskell class for undergraduates. This is the second time I've taught it. The last time, for their final project I gave them the option of contributing to an open-source project; a couple groups took me up on it and I think it ended up being a modest success. So I'd like to do it again this time around, and am looking for particular projects I can suggest to them. Do you have an open-source project with a few well-specified tasks that a relative beginner (see below) could reasonably make a contribution towards in the space of about four weeks? I'm aware that most tasks don't fit that profile, but even complex projects usually have a few "simple-ish" tasks that haven't yet been done just because "no one has gotten around to it yet". If you have any such projects, I'd love to hear about it! Here are a few more details: * The students will be working on the projects from approximately the end of this month through the end of April. * By "relative beginner" I mean someone familiar with the material listed here: http://www.cis.upenn.edu/~cis194/lectures.html and just trying to come to terms with Applicative and Monad. They definitely do not know much if anything about optimization/profiling, GADTs, the mtl, or Haskell-programming-in-the-large. (Although part of the point of the project is to teach them a bit about programming-in-the-(medium/large)). * What I would hope from you is a willingness to exchange email and/or chat with the student(s) over the course of the project, to give them a bit of guidance/mentoring. I am certainly willing to help on that front, but of course I probably don't know much about your particular project. thanks! -Brent

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