- Haskell-Cafe - Haskell.org

libmad and os/x coreaudio wrappers
by Chris Waterson 19 Mar '08

19 Mar '08

Hi there! I've taken my first stab at writing some (admittedly minimal) libraries for Haskell, and would love to get feedback on them: * hmad: a wrapper for the libmad MP3 decoder. http://maubi.net/~waterson/REPO/hmad * CoreAudio: a wrapper for OS/X CoreAudio. http://maubi.net/~waterson/REPO/CoreAudio (You should be able to "darcs get" the above links, if you want.) I wrote the libmad wrapper to generate a "stream" (i.e., a lazy list) of audio samples. CoreAudio allows the input stream to be lazy, as well. So, here's a simple MP3 player: > module Main where > > import Sound.CoreAudio > import Codec.Audio.MP3.Mad > import qualified Data.ByteString.Lazy as B > import System > import System.IO > > main :: IO () > main = do files <- getArgs > mapM_ playFile files > > playFile :: String -> IO () > playFile file = > withBinaryFile file ReadMode $ \ inHandle -> > do xs <- B.hGetContents inHandle > samples <- decode xs > play samples I do have a couple questions... * The CoreAudio library requires its users to be compiled with "-threaded". Is there a way to specify that in the Cabal file? * I wanted to be able to generate a variety of streams from libmad. Besides stereo linear PCM data, it also seemed like it might be worth-while to produce a stream of MP3 frame headers, the unsynthesized frequency domain data, and so on. I tried to accomplish this with a the DecoderSink class, but I'm not sure I succeeded. Any thoughts here would be appreciated! I hope someone else finds these useful. The FFI was a joy to use once I figured it out... :) chris

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ghc 6.8.2 and timer_create error
by Anatoly Yakovenko 19 Mar '08

19 Mar '08

I have a gentoo box with ghc 6.8.2, and the binaries that ghc builds on that box do not work on redhat EL 4 or ubuntu 7.10. When I try to run the binary, i get an error: Main: timer_create: Invalid argument so is there any way to get ghc to build a binary that doesn't use timer_create? or is that something that is configured when ghc itself is built, if so, how do I turn that feature off? Thanks

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Satnam Singh of Microsoft Research
by Galchin Vasili 19 Mar '08

19 Mar '08

Hello, Recently Satnam Singh of Microsoft Research gave a talk at Google about concurrency, Haskell STM, etc. Was there a transcript of this talk? Thanks, Vasili

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Dynamic typing makes you more productive?
by Justin Bailey 19 Mar '08

19 Mar '08

>From a recent interview[1] with the guy leading Ruby development on .NET at Microsoft: "You spend less time writing software than you spend maintaining software. Optimizing for writing software versus maintaining software is probably the wrong thing to do. Static typing makes it harder to maintain software because it's harder to change it." Two years ago I would have agreed with that statement. Now - no way. Make the compiler work for you. I've done a lot of Ruby development and I would never use it for a project of more than 3 or 4 people. It's an awesome language but I don't think it would scale to programming "in the large." Any object can be modified at any time. Determining where a particular method comes from can be an exercise in Sherlockian deduction. Give an organization of 100 developers that much freedom and I can only imagine chaos would result. Justin [1] http://www.regdeveloper.co.uk/2008/03/17/ironruby_work_schedule/

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Re: [Haskell-cafe] build recent(ish) ghc on macos 10.3.9 powerpc?
by Uwe Hollerbach 19 Mar '08

19 Mar '08

Hello, haskellers, a few days ago I had asked about building recent ghc on macos 10.3.9. I have made a bit of progress along those lines, here's a small update on what worked and what didn't. Instead of trying to proceed with the porting procedure, I went back to an install: I ended up going to 6.2.2. After a bit of fiddling, I found that another bit of messing-about I had done to the machine was messing me up: I had upgraded gcc from 3.3.x to 3.4.6 by just downloading the sources and building. That produced a working gcc 3.4.6, but apparently the apple-aware ghc 6.2.2 and the apple-unaware gcc 3.4.6 didn't play nicely together. Once I disabled gcc 3.4.6, stuff worked again. Then I tried building ghc 6.4.2 using the installed 6.2.2. This took a lot of time, the compiler was able (as far as I could tell) to go through all of its own bootstrapping, but after I happily installed what I thought was a working ghc 6.4.2, the installed version was unable to do anything: it segfaulted while trying to do "ghc --version". Oops... Out of somewhat morbid curiosity, I tried running that inside the debugger, but gave up after several hours of elapsed time. Back to the drawing board. So I tried jumping directly from 6.2.2 to 6.6.1; that is, using 6.2.2 to build 6.6.1. That took another lot of time, but I'm happy to report that it has produced a working executable: it did proceed all the way through its bootstrapping, I verified that the executable in compiler/stage2 was able to run "ghc --version" in-place, and after I installed it, it was still able to do that; and (extra bonus! :-) ) it's also able to compile and link at least one small Haskell program written by me! Cool! I'm going to keep going forward and try to build 6.8.2, and I'll report back if that succeeds, but this is already pretty good progress... regards, Uwe

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Re: [Haskell-cafe] intersection of sets
by Tim Chevalier 18 Mar '08

18 Mar '08

[ccing to list] On 3/18/08, Walt Potter <potter(a)southwestern.edu> wrote: > Tim, > > We're using -O2 to optimize, but not changing the heap size. We're > trying to get the profiling running on our file. > The sets have about 25 million elements each. Each element is a sequence > of length 16. > > We'll want to compute larger examples! > > I do not know how intersection works in Data.Set. I'm worried that we're > having problems with stack overflow due to recursion. We'll try to > remove the lazy stuff. > Run profiling before you "try to remove the lazy stuff". There's no point in trying to optimize code until you know what's actually taking up space. If you have problems with profiling, then ask on the glasgow-haskell-users mailing list. Cheers, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt "Aw, honey, you can keep what's in my pockets, but send me back my pants." --Greg Brown

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intersection of sets
by Walt Potter 18 Mar '08

18 Mar '08

All, We're running out of space when we intersect two large sets. We've imported Data.Set. Any suggestions? Thanks, Walt

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[Haskell-cafe] type families, fun deps, lattices imposed on/by types
by Isto Aho 18 Mar '08

18 Mar '08

Hi all, I was trying to solve a problem and by chance found texts on functional dependencies and then on type families (papers, ghc docs). Please, consider the example 03 of "Understanding functional dependencies via Constraint Handling rules" by Sulzmann, Duck, Peyton-Jones and Stuckey. There we are defining a multiplication over different numeric types: class Mul a b c | a b -> c where (*) :: a -> b -> c instance Mul Int Int Int where ... instance Mul Int Float Float where ... Ok, we could add instance Mul Float Int Float where ... but if we want to make everything work nicely together, Integer, Complex, Rational etc, there will be a lot of instances, especially if we have to give both "Float Int" and "Int Float" instances. And now the question on "lattices of types" (didn't know any better name to refer to the following): Is the following possible? Or can something similar achieved with type families (easily)? type lattice T a b -- Each of the following gives a "<"-relation between types, -- "upper" gives a method, how we get the larger (2nd) from -- the smaller (1st). lattice instance T Int Integer where upper = fromIntegral lattice instance T Int Float where upper = fromIntegral lattice instance T Integer (Ratio Integer) where upper = ... lattice instance T (Ratio Integer) Double where ... lattice instance T Float Double ... lattice instance T Double (Complex Double) ... -- e.g. Now the compiler can check that the top type is -- unique and that there is a path from every type to the top type. -- If the compiler founds this not to be the case, an error is output. -- But otherwise there can be types that are not comparable but -- the common top is quaranteed to exist. class Mul a b c where lattice T (*) :: a -> b -> c (*) x y = (upper x y x) * (upper x y y) -- Now there is no need for the instances like. instance Mul Int Float Float where ... instance Mul Float (Ratio Integer) Double where ... The compiler can generate those instances, because we have given the "upper"-methods. There is always the top available. Function (*) x y = (upper x y x) * (upper x y y) might could be replaced with (*) x y = x * y because of the presence of lattice T and thus, the "upper"-function. If this were possible, the benefits would be: - No need to state "Int Float" and "Float Int" instances on cases where the operands do commute. - No need to write a large number of instances if you have several "types on lattice" (e.g. some more or less well defined relation). - If the relation between types is not clear, we could define another lattice T2 to our Mul2 class for the other uses. Continuing the idea: we could override the default instances generated by the compiler with our own instances when needed. Ok, so, is it possible to write something like that already? (I just wouldn't like write a lot of instances...) If not, would it be possible to extend, say ghc, to work that way or are there too much inconsistencies in the above presentation? (Yes, where is the bottom. Why top and not bottom? Should it be possible to tell, which one to use, if both present? e.g.) Thanks for reading this far! -- br, Isto

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Two Lectureships in Nottingham
by Graham Hutton 18 Mar '08

18 Mar '08

Dear all, We are advertising two new Lectureships (Assistant Professorships) in Computer Science at the University of Nottingham in England. Applications in the area of functional programming are particularly welcome. Further details are available from: http://jobs.nottingham.ac.uk/vacancies.aspx?cat=160#j2797 The closing date for applications is 28th March 2008. Best wishes, Graham Hutton +-----------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | School of Computer Science | | University of Nottingham Web : www.cs.nott.ac.uk/~gmh | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB, UK Phone : +44 (0)115 951 4220 | +-----------------------------------------------------------------+ This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Re: ANN: Parsec 3.0.0
by John MacFarlane 18 Mar '08

18 Mar '08

> * A "compatibility" Text.ParserCombinators.Parsec tree for the old > Parsec. It's not perfect, but it should work with most Parsec 2 > code. A data point: I recompiled pandoc with the new Text.ParserCombinators.Parsec compatibility module, and performance is much worse than with parsec 2.1 (approximately twice as slow on my standard benchmark). That aside, this is a very welcome release! John

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