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returning lists
by raptor 01 Dec '05

01 Dec '05

hi, i'm having this problem, tring to implement split (for learning purposes). Here is one sample of my tries : split _ [] = [] split char (x:xs) | x /= char = x : split char xs | otherwise = [] it is ok i.e. it returns the first of the splits, but I want to get all of the results. str = "testingxsplitxtoxseexhowxitxwork" *Main> split 'x' str "testing" I want : ["testing","split",...] How do i do this.

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RE: [Haskell-cafe] STM, orElse and timed read from a channel
by Simon Marlow 01 Dec '05

01 Dec '05

On 29 November 2005 13:01, Joel Reymont wrote: > Would you share your implementation for us advanced users? It's a modification of GHC.Conc, so I can't supply a standalone implementation I'm afraid. > I could use Tomasz's workaround in the meantime but isn't GHC 6.6 > supposed to be out in a year? Rather less than a year, I hope. Cheers, Simon

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:t main
by Scherrer, Chad 01 Dec '05

01 Dec '05

I've been reading some of the articles about comonads, and I thought the idea of giving main the type OI () -> () was pretty interesting. So I was wondering, would it be possible to allow the type of main to be inferred? It seems like IO () OI () -> () OI () -> IO () all make sense (at least I think they do). One particularly nice side effect of this (pardon the pun) is that a good number of useful programs can be written as getContentsW :: OI () -> a doSomeStuff :: (Show b) => a -> b print :: (Show b) => b -> IO () main = print . doSomeStuff . getContentsW so much less understanding about monads et al is required to do some basic stuff. I think it would be much easier in this case to make the transition to Haskell. Also, has anyone given any thought to syntactic sugar for comonads? Since arrows and monads share the (<-) symbol, it seems like a nice unification could be possible... Maybe (-<) alone could be used similarly? Thanks, Chad Scherrer

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RE: [Haskell-cafe] Detecting Cycles in Datastructures
by Simon Peyton-Jones 01 Dec '05

01 Dec '05

| Andrew Pimlott: | //about my highly spiritual essay on lazy computing of PI//: | | > In addition to being clever and terribly funny, the conclusion | > foreshadows (inspired?) later work on Enron [1]. | | Come on, it is improbable that Master Simon ever read my essay... I hadn't before, but I have now. Cool stuff. I once wrote a continued-fraction package with the something of the same flavour (since overtaken by David Lester's work, which to my deep sadness remains unpublished to this day). Your code clearly belongs in the nofib suite, as a splendid way to consume compute cycles and test compilers. Do send me a Main.hs to compute pi, with a changeable runtime (presumably just adjust 'take'). Simon

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first post
by raptor 01 Dec '05

01 Dec '05

hi, I'm trying to figure out how to parse a text file, but these type-conversations are just killing me! Whats wrong with following code : module Main where main = putStrLn "hi" parse str = take 10 str load = do content <- readFile "parse.hs" return content when try : Prelude> parse load <interactive>:1:6: Couldn't match `[a]' against `IO String' Expected type: [a] Inferred type: IO String In the first argument of `parse', namely `load' In the definition of `it': it = parse load i tried different combinations, but still cant figure out... How do u use an "IO String" in normal "String" functions.. I want to particulary slurp file in a string and then make funny things with it...spliting to lines,parsing them and building hash like strucutre of it...etc. later i want to try spliting,regex-es..etc. It is very hard to figure out how to use these modules.. :"(

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first post
by Chad Scherrer 01 Dec '05

01 Dec '05

Because the load function interacts with the outside world, its type involves the IO monad. You can get the result you're looking for using something like liftM parse load liftM takes an ordinary function and applies it to a monadic value (here the monad is IO), returning another monadic value. Or, if you're using ghci, you could just do s <- load parse s This is because ghci executes "in the IO monad" (maybe there are some details of this I'm missing, but that's how I think of it anyway. BTW, your load function could be equivalently written simply as load = readFile "parse.hs" -Chad Scherrer

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Oops, Hsc license is clearly GPL in the Hsc.cabal file was Re: Hacking Haskell in Nightclubs?
by rd＠slavepianos.org 30 Nov '05

30 Nov '05

> My mistake, the Hsc.cabal file clearly states GPL. (I assume I can choose > either GPL v1 or v2 ?) The SuperCollider server is GPL v2. As this is just an interface to the server, I think it should have the same license. I haven't worked out about the Cabal yet, but it's on my todo list, and then I'll make the version number explicit. Rohan

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Hacking Haskell in Nightclubs?
by rd＠slavepianos.org 30 Nov '05

30 Nov '05

Real-time audio is much simpler these days due to SuperCollider, a truly excellent cross platform audio synthesis server by James McCartney. http://www.audiosynth.com http://supercollider.sf.net To communicate with the server one only needs to implement the most basic aspects of the Open Sound Control (OSC) byte protocol (in particular none of the pattern matching is required). http://www.opensoundcontrol.org/ To define 'instruments' there is a SuperCollider specific byte protocol for describing Unit Generator (UGen) graphs. I have an initial Haskell implementation of both these protocols at: http://www.slavepianos.org/rd/f/207949/ darcs get http://www.slavepianos.org/rd/sw/sw-69/ If SuperCollider is running on the local host at the usual port then: Hsc*> play' sc ab Hsc*> stop' sc should play (and then stop playing) the famous 'Analog Bubbles' test sound: ab = out AR 0 $ combn AR s 0.2 0.2 4 where s = sinosc AR (midicps f) 0 * 0.1 f = lfsaw KR 0.4 0 * 24 + o o = lfsaw KR (MCE [8, 7.23]) 0 * 3 + 80 The Hsc module can also write UGen graphs to the 'dot' language, so graphs can be drawn automatically, which can be useful for debugging. I have been working with scheme and SuperCollider for some time, but have been using haskell recently and generally like it very well. I don't think static typing is an issue. OSC messages can be timestamped, and SuperCollider has a sample accurate scheduling queue, so language timing jitter can easily be worked around. I think that the SuperCollider model is an excellent fit with languages like Haskell. Regards, Rohan On Mon Nov 28 21:35:38 EST 2005 Paul Hudak wrote: > Although Haskore (haskell.org/haskore) doesn't currently support > real-time music, it's something I've thought about numerous times in the > past, and wish I had the time to do it... > > -Paul Hudak > > > Echo Nolan wrote: > > Hello all, > > I read an article on using perl for live improvised synthesis a > > while ago (http://www.perl.com/pub/a/2004/08/31/livecode.html) Does > > anyone have thoughts in doing this is haskell? Would strong typing make > > "jazzy" programming too difficult?

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type inference algorithm for type classes
by robert wong 30 Nov '05

30 Nov '05

Hi All, I have been developing a type inference system which is very similar to type classes' (by Wadler and Blott). However, I cannot find a detailed description of the algorithm. In "Type Classes in Haskell", implementation issues are discussed briefly. However, it is too brief for me to grasp. Does anybody have any suggestion on where to look? Thanks, Robert _________________________________________________________________ Get an advanced look at the new version of MSN Messenger. http://messenger.msn.com.sg/Beta/Default.aspx

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RE: [Haskell-cafe] STM, orElse and timed read from a channel
by Simon Marlow 29 Nov '05

29 Nov '05

On 29 November 2005 12:47, Joel Reymont wrote: > Where is this "registerTimeout" in the GHC code? Well, it's not there yet :-) But I've hacked up an implementation this morning so it might be in GHC 6.6. Cheers, Simon

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