- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Num instances for 2-dimensional types
by Brad Larsen 05 Oct '09

05 Oct '09

On Mon, Oct 5, 2009 at 10:36 AM, Miguel Mitrofanov <miguelimo38(a)yandex.ru> wrote: [...] > Of course, it's OK to call anything "numbers" provided that you stated > explicitly what exactly you would mean by that. But then you have to drop > all kind of stuff mathematicians developed for the usual notion of numbers. > In the same way, you shouldn't use the "Num" class for your "numbers". > > On the other hand, people can (ab)use the "Num" class as they wish, and it's > their business until they ask a question about it somewhere outside - which > makes the business not only theirs. [...] The Num class has `negate' as part of its definition. Natural numbers are numbers, but I don't believe there is any sensible definition of `negate' for them. Haskell 98's numeric hierarchy combines many operations which should be separate. As further evidence, every bit of Haskell I have seen that does symbolic manipulation of numeric expressions either leaves out instances that would make the syntax more convenient, or else defines partial instances because certain class functions have no sensible definition for symbolic expressions. Sincerely, Brad

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apply function arguments in a list
by Michael Mossey 05 Oct '09

05 Oct '09

If I have a list containing the arguments I want to give to a function, is there a general way to supply those arguments in a compact syntax? In other words, I could have args = [1,2,3] f x y z = ... I would write t = f (args!!0) (args!!1) (args!!2) but there may be a neater, more general syntax. I tried writing a fold with $, but I don't think that works because the type of each step is different. I.e. f :: a -> a -> a -> a f x :: a -> a -> a f x y :: a -> a f x y z :: a This would seem to preclude a general way of writing a function that supplies arguments from a list.

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ICFP videos now available
by Wouter Swierstra 05 Oct '09

05 Oct '09

I am happy to announce that videos of all talks at ICFP and some of the associated workshops this year have made available online: http://www.vimeo.com/user2191865/albums I'm sure you'll join me in thanking Malcolm Wallace for the time and effort he put into making this possible. Thank you Malcolm! Wouter

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Is c2hs able to generate FunPtr rather than just the function?
by Rafal Kolanski 05 Oct '09

05 Oct '09

Hi Everyone, I'm trying to figure out an elegant way of letting the Haskell garbage collector deal with structures allocated from C. So I have the C pair: fluid_event_t* new_fluid_event(void); void delete_fluid_event(fluid_event_t* evt); I've handled the new_fluid_event thing nicely, ForeignPtr and all. Now if I want to add a finalizer to the ForeignPtr via newForeignPtr, and for that I need a FunPtr. So what I need is: foreign import ccall safe "fluidsynth.h &delete_fluid_event" deleteFluidEvent'' :: FunPtr (((Ptr (Event)) -> (IO ()))) (if I use that as a finalizer, everything works nicely) But the closest I can get to generating something similar with c2hs is: {# fun delete_fluid_event as ^ {fromEvent `Event'} -> `()' #} which results in: foreign import ccall safe "Event.chs.h delete_fluid_event" deleteFluidEvent'_ :: ((Ptr (Event)) -> (IO ())) Is there a neat way to have c2hs generate the FunPtr version for me? Sincerely, Rafal Kolanski.

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ANN: TxtSushi 0.4.0
by Keith Sheppard 05 Oct '09

05 Oct '09

Hello Cafe, I've just uploaded TxtSushi 0.4.0 to hackage. TxtSushi is a collection of command line utilities for processing comma-separated and tab-delimited files. I posted details on my blog (along with an advertisement to see if others are interested in hacking TxtSushi): http://blog.keithsheppard.name/2009/10/txtsushi-040.html Best Regards Keith -- keithsheppard.name

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Fwd: [Haskell-cafe] killer app sought
by Alberto G. Corona 04 Oct '09

04 Oct '09

Yes, Maybe The piece of the web that desperately need a boost in performance, declarativeness, safety, static typing threading, modularity etc etc etc is the Web Browser. 2009/10/4 John A. De Goes <john(a)n-brain.net> > With few exceptions, no such thing as a killer server-side app. > > The Web 3.0 paradigm is simple: all work except sharing and persistence of > data is done on the client. > > Regards, > > John A. De Goes > N-Brain, Inc. > The Evolution of Collaboration > > http://www.n-brain.net | 877-376-2724 x 101 > > > On Oct 3, 2009, at 9:08 PM, Mark Wotton wrote: > > Hi, >> >> I've been writing a little binding from Ruby to Haskell called Hubris ( >> http://github.com/mwotton/Hubris) which I think has some potential both >> for making Haskell web apps easier to write, and also for bringing the more >> adventurous Ruby programmers into the Haskell community. Code-wise it's >> coming along nicely, and once 6.12 is out it'll run without modifications at >> least on Linux (remains to be seen how long it'll take to get the Mac >> patches into shape). My real problem is marketing: I need a killer app that >> shows it's easy either to >> >> 1. wrap a kickarse Haskell library in a convenient Ruby web app shell >> 2. speed up a poorly performing Ruby web app >> >> I've been badgering the Ruby guys in Sydney that I know on the second >> point, but either none of them have performance problems, or none of them >> want to admit it. The first is entirely possible - if you only attack the >> subset of problems where your runtime is dominated by the database and >> network latency, language performance is moot. Conversely, if that's your >> worldview, the other problems that could be attacked won't ever come to mind >> (to monstrously abuse the Sapir-Whorf hypothesis). >> >> So, I'm asking you guys. What are some really nice Haskell libraries or >> apps that could benefit from being shown off in one of the plethora of >> slick, mature web frameworks that exist in Ruby? Manuel Chakravarty >> suggested something with vector operations in order to take advantage of his >> 'accelerate' library (once it gets a GPU backend, of course), and more >> generally, something taking advantage of Haskell's support for multicore >> would be cool. (The standard edition of Ruby is still unicore, I believe.) >> >> Parenthetically yours, >> Mark >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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killer app sought
by Mark Wotton 04 Oct '09

04 Oct '09

Hi, I've been writing a little binding from Ruby to Haskell called Hubris (http://github.com/mwotton/Hubris ) which I think has some potential both for making Haskell web apps easier to write, and also for bringing the more adventurous Ruby programmers into the Haskell community. Code-wise it's coming along nicely, and once 6.12 is out it'll run without modifications at least on Linux (remains to be seen how long it'll take to get the Mac patches into shape). My real problem is marketing: I need a killer app that shows it's easy either to 1. wrap a kickarse Haskell library in a convenient Ruby web app shell 2. speed up a poorly performing Ruby web app I've been badgering the Ruby guys in Sydney that I know on the second point, but either none of them have performance problems, or none of them want to admit it. The first is entirely possible - if you only attack the subset of problems where your runtime is dominated by the database and network latency, language performance is moot. Conversely, if that's your worldview, the other problems that could be attacked won't ever come to mind (to monstrously abuse the Sapir-Whorf hypothesis). So, I'm asking you guys. What are some really nice Haskell libraries or apps that could benefit from being shown off in one of the plethora of slick, mature web frameworks that exist in Ruby? Manuel Chakravarty suggested something with vector operations in order to take advantage of his 'accelerate' library (once it gets a GPU backend, of course), and more generally, something taking advantage of Haskell's support for multicore would be cool. (The standard edition of Ruby is still unicore, I believe.) Parenthetically yours, Mark

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Where do these warnings come from?
by Colin Paul Adams 04 Oct '09

04 Oct '09

Does anyone recognize which module/function would emit the following warnings? WARNING: nonstandard use of escape in a string literal LINE 11: '# Pandoc\r\n\r\nPandoc is a program for converting ... ^ HINT: Use the escape string syntax for escapes, e.g., E'\r\n'. -- Colin Adams Preston Lancashire

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Need some help with Alex macros
by Niklas Broberg 04 Oct '09

04 Oct '09

Hi all, I'm going crazy trying to get Alex to do what I want. I have the following regexp macros: @octEscape = [0123]? $octdig{1,2} @hexEscape = 'u' $hexdig{4} @charEscape = '\\' (@octEscape | @hexEscape | b | t | n | f | r | \" | \') and the following rules: \' (. # [\'\\] | @charEscape) \' { \p s -> CharTok (readCharTok s) } \" (. # [\"\\] | @charEscape)* \" { \p s -> StringTok (readStringTok s) } I've tried a lot of variations on where to put the backslashes and quotes to get it to do what I want, what you see above is just one variation, but no matter what I try I can't get it to work. > alexScanTokens $ show '\n' *** Exception: lexical error Can anyone help shed some light on this for me? Why can't I get alex to recognize escapes inside character literals? Cheers, /Niklas

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ANNOUNCE: SourceGraph 0.5.2.0
by Ivan Lazar Miljenovic 04 Oct '09

04 Oct '09

Yes, this is yet another SourceGraph announcement, this time for version 0.5.2.0 [1]. [1] http://hackage.haskell.org/package/SourceGraph-0.5.2.0 The changes in this release are as follows: * Shift overall analysis to the top and per-module analysis to the end, as suggested by Duncan Coutts. * Graph drawing fixups: instances are now drawn correctly, and the module graph now has modules located in the correct directory. * Improve some graph drawing aspects (node margins, colours for module graphs, etc.). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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