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Does Hackage have a connection to some SFT package (Significant FFT coefficients) ...
by caseyh＠istar.ca 06 Aug '10

06 Aug '10

Does Hackage have a connection to some SFT package (Significant FFT coefficients) and/or can one get the SFT from FFTW without generating all the coefficients?

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real-time audio processing [Was: can Haskell do everyting as we want?]
by Stephen Sinclair 06 Aug '10

06 Aug '10

On Aug 3, 8:31 pm, Jeremy Shaw <jer...@n-heptane.com> wrote: > The only area I have had any trouble with Haskell is doing realtime > music synthesis. And only because the garbage collector is not > realtime friendly. That is not unfixable though. However, I am > thinking that the best way to do realtime synthesis with Haskell is to > use it to create a DSL that uses LLVM to create code at runtime so > that the realtime code is outside the scope of the normal RTS and > garbage collector. I'm also very interested in this topic---how to apply a general- purpose functional language to real-time needs, even if it is in a domain-specific way. Indeed, it mostly comes down to memory management and the fact that functional concepts like closures and laziness require a lot of dynamic allocation and garbage collection. Certainly, one solution is to provide a real-time-friendly memory manager. However, it's interesting to notice that, as proven by FAUST [1], a huge amount of DSP algorithms can be expressed functionally in a real- time-compatible way by describing them as static diagrams of connected blocks. These can be efficiently compiled to imperative code with no dynamic memory allocation required. So yes, if such a language were available as an embedded DSL in Haskell (one effort can be found here [2]), it could be generated at run-time using LLVM and called out to. Alternatively, it would be very cool if it were possible to generate code statically at compile time, just like in FAUST. I can imagine this being very useful, especially if it could be generalized to operate on datatypes other than floating points, and had easy access to data structures provided by non-RT portions of the code. If there are mutability requirements, it could be made to run in the ST monad with a pre-allocated workspace. Of course _modifying_ such structures at run-time is always a dynamic thing by definition, although there is the possibility of dynamically generating a replacement block diagram while an one existing one runs, and using an atomic pointer swap to switch them without causing interruptions. In any case, as far as I know the only thing in the way is that it's impossible to tell GHC to compile a section of code in such as way as to guarantee avoidance of memory management. Compilers and runtime- systems always seem to be either RT- or non-RT-friendly, but never seem to support the idea of code *portions* that have differing requirements. My point is, RT code _can_ be expressed functionally, even if the RT-ness imposes certain expressivity restrictions. It would be very cool to be able to mark sections of code as following such a "sub-language" and be guaranteed that the compiler will generate GC-free code for a particular function, if possible, or otherwise fail. Even if such a sub-language were no more expressive than C, it would be nice to be able to write it in Haskell instead of dropping down to C, so that data can be easily shared with non-RT parts, and Haskell's type checker could be exploited. It seems strange to me that with technology like Haskell and GHC we still depend on using C to express these last remaining droplets of real-time determinism requirements--- strange, since I think of higher-level languages like Haskell to be supersets of the capabilities of C---and annoying, because it means having to deal with the complexities of language interoperability, just for a few low-level components of an application. I realize some of this has probably been discussed in conjunction with FRP. I'm aware of one paper on RT-FRP that talks about requiring an RT-friendly sub-language [3], but I don't pretend to follow it completely. I'm almost sure it also has something to do with arrows, but I have very little idea what they are, since I'm still just "getting" monads at this point in my personal Haskell understanding. I hope someone more knowledgeable about these things on this list might be able to comment on their relation to real-time determinism. [1] http://faust.grame.fr/ [2] http://claudiusmaximus.goto10.org/cm/2009-12-04_heist_dataflow_algebra.html [3] http://www.haskell.org/frp/rt-frp.pdf

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Question about rpc design
by lysgaard 06 Aug '10

06 Aug '10

Hi, I'm tinkering with making a DHT im my spare time this summer. For this i need to do some unusual rpc calls. You see in a dht a query (rpc) is first sent from you (node "a") to a node "b" which probably doesn't know the answer. If it still does know the answer it returns the value of the query to node "a". This gives the latency: 2*latency(a,b) On the other hand, if i t doesn't it sends a new rpc to a node "c" more probable to know the ansver. Then the latency is: latency(a,b) + 2*latency(b,c) + latency(b,a) While what I would like is this: latency(a,b) + latency(b,c) + latency(c,a) you see that for many forwards this adds considerable latency and also many more calls than nessesary. Is this way of sending messages already known? Does it have a name? And if not, how hard do you think it would be to hack some rpc library to implement this? -- View this message in context: http://old.nabble.com/Question-about-rpc-design-tp29356441p29356441.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Wildly off-topic: de Boor's algorithm
by Andrew Coppin 06 Aug '10

06 Aug '10

Given a suitable definition for Vector2 (i.e., a 2D vector with the appropriate classes), it is delightfully trivial to implement de Casteljau's algorithm: de_Casteljau :: Scalar -> [Vector2] -> [[Vector2]] de_Casteljau t [p] = [[p]] de_Casteljau t ps = ps : de_Casteljau t (zipWith (line t) ps (tail ps)) line :: Scalar -> Vector2 -> Vector2 -> Vector2 line t a b = (1-t) *| a + t *| b Now if you want to compute a given point along a Bezier spline, you can do bezier :: Scalar -> [Vector2] -> Vector2 bezier t ps = head $ last $ de_Casteljau t ps You can chop one in half with split :: Scalar -> [Vector2] -> ([Vector2], [Vector2]) split t ps = let pss = de_Casteljau t ps in (map head pss, map last pss) And any other beautiful incantations. Now, de Boor's algorithm is a generalisation of de Casteljau's algorithm. It draws B-splines instead of Bezier-splines (since B-splines generalise Bezier-splines). But I think I may have ACTUALLY MELTED MY BRAIN attempting to comprehend it. Can anybody supply a straightforward Haskell implementation?

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what's the best environment for haskell work?
by Rustom Mody 06 Aug '10

06 Aug '10

Do most people who work with haskell use emacs/vi/eclipse or something else?? Personal Note: I used gofer some 15 years ago. At that time I hacked up a emacs mode (I did not know of any then) along with some changes to gofer to have gofer inside emacs rather than vi inside gofer. Things have got more exciting now -- just trying to catch up!! [Note: My preferrred/default OS is debian-squeeze]

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Re: using Network.CGI
by Anders Kaseorg 06 Aug '10

06 Aug '10

On Thu, 5 Aug 2010, Andrew U. Frank wrote: > which is clearly not producing the second part of the code, namely > output a greeting. That’s what it’s supposed to output. Have you considered typing in a name and submitting the form? It works fine for me: <http://andersk.mit.edu/greet.cgi>. > i try to use the Network.CGI package from darcs. (Note also that the current version is maintained in Git, not Darcs, but that’s a minor detail. See http://hackage.haskell.org/package/cgi .) Anders

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Re: [Haskell-cafe] subversion with haskell
by Yuras Shumovich 06 Aug '10

06 Aug '10

Hi, Try the next: % env EXTRA_CPPFLAGS="-I/usr/local/include/subversion-1" \ EXTRA_LDFLAGS="-L/usr/local/lib" \ runhaskell Setup.hs configure % runhaskell Setup.hs build % runhaskell Setup.hs install (and read the installation instructions included into the tarball :) ) 2010/8/5 Andrew U. Frank <frank22(a)geoinfo.tuwien.ac.at>: > i found the file in usr/include/subversion-1 (i use an ubuntu (debian) > installation form). but the cabal installer (i.e. the configure script) > does not find the file. > > can you give me a hint where it could search and where i could copy the > file to. i tried to read the configure script, but cannot see, where it > searches. i am not familiar with cpp and do not understand what the hint > 'extra cpp flags' could mean. > > thanks for your help! > > andrew >

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Why do "unsafe" foreign calls block other threads?
by Gregory Crosswhite 05 Aug '10

05 Aug '10

Hey everyone, Could someone explain to me the logic behind having "unsafe" calls block other threads from executing? It seems to me that if anything it would make more sense for "safe" calls to block other threads since the call can call back into the Haskell runtime, as opposed to "unsafe" calls which (by assertion) will never call back into Haskell and therefore should be safer to run in parallel with other threads. What am I missing here? Cheers, Greg

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network.cgi - incomplete translation of code to javascript
by Andrew U. Frank 05 Aug '10

05 Aug '10

i try to use the Network.CGI package from darcs. my testing uses the example code from the webpage 'practical web programming in haskell' http://www.haskell.org/haskellwiki/Practical_web_programming_in_Haskell#Get… specifically the example with code: import Network.CGI import Text.XHtml inputForm = form << [paragraph << ("My name is " +++ textfield "name"), submit "" "Submit"] greet n = paragraph << ("Hello " ++ n ++ "!") page t b = header << thetitle << t +++ body << b cgiMain = do mn <- getInput "name" let x = maybe inputForm greet mn output $ renderHtml $ page "Input example" x main = runCGI $ handleErrors cgiMain -- Get the value of an input variable, for example from a form. -- If the variable has multiple values, the first one is returned. -- getInput :: String -> CGI (Maybe String) this runs (runghc) and produces the output: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" ><head ><title >Input example</title ></head ><body ><form ><p >My name is <input type="text" name="name" id="name" /></p ><input type="submit" value="Submit" /></form ></body ></html > which is clearly not producing the second part of the code, namely output a greeting. the same happens with the next example, using cookies, where from two options for pattern matching only the first is include in the javascript. i assume that i do something wrong - but what? any help is appreciated! andrew

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jswm - how to manipulate strings?
by Andrew U. Frank 05 Aug '10

05 Aug '10

i try to use jswm to build some web applications, but i got quickly stuck. I used the example programs provided and tried to change them. starting with the calculator, i would like to use the string that the user puts in and apply a function to it (say transform it to capitals, later i want to do more complex operations). now i cannot find a way to apply a function to the type returned from the input: get'value :: (Monad mn, CHTMLTextAreaElement this) => Expression this -> mn (Expression String) how can i apply some function to the string in the input : mn (Expression String) ? or how can i get the string out such that i can change it and later put it back into an expression? help is appreciated - there seems to be only a small piece missing.. andrew

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