October 2009 - Beginners

count function
by John Moore 18 Oct '09

18 Oct '09

Hi, Trying to get aprogram to count all the lines or words from a file. Not sure about the syntax. Probably missing some. Here's what I have so far any help in the right direction would be great. import System.IO main :: IO () main = do incom <- openFile "file.txt" ReadMode otcom <- openFile "prob.txt" WriteMode fCount incom otcom hClose incom hClose otcom fCount incomh otcomh = do eof <- hIsEof incomh if eof then return() else do c <- hGetCount incom it tells me parse error on = John

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I/O
by John Moore 18 Oct '09

18 Oct '09

Hi, Could someone please tell me how to check this program. The problem is where do I find the output? I laod this into ghc and it comes up OK modules loaded: Main gchi> How do I now check if it works or see the result. Program below (taken from real world haskell) -- file: ch07/toupper-imp.hs import System.IO import Data.Char(toUpper) main :: IO () main = do inh <- openFile "quux.txt" ReadMode outh <- openFile "output.txt" WriteMode mainloop inh outh hClose inh hClose outh mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if ineof then return () else do inpStr <- hGetLine inh hPutStrLn outh (map toUpper inpStr) mainloop inh outh John

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is there a best os to easily install external libraries ?
by david hodgetts 17 Oct '09

17 Oct '09

Hello everyone, to give some context: I am not a real developer. I am a motion designer who enjoys doing procedural animations and installations with tools such as processing, flash, openframeworks. This might explain some of the difficulties I describe below. Wanting to broaden my thinking skills and CS knowledge, I have started to learn Haskell, and I must say I am having a great time. I am at a point now where I would like to play around with some of the popular UI and graphical libraries (gtk+, freeGlut, sdl etc). But my experience up to now has been a bit painfull in the sense that most of these packages don't install nicely with caball ( on windows XP). I managed to get gtk, freeglut, and curl to install after long hours googling around and doing voodoo in msys and cygwin. Last night I tried to install the SDL bindings to follow a blog post about automata, but completely failed. This got me to wondering if the haskell experience with regards to installing external libraries might be any easier on Linux? in advance many thanks best regards david hodgetts

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sorting by elements in a tuple
by Ryan Temple 16 Oct '09

16 Oct '09

I am wanting to sort a list of tuples by the first and then the second item in the tuple. So [(1,2),(4,2),(2,5)] would become [(1,2),(2,5),(4,2)] I am attempting to use the Sorty function but don't seem to be having much luck tuplesort :: [(a,b)] -> [(a,b)] tuplesort [(_,_)] = sortBy (comparing fst) -- this is an attempt to organise by the first element in the tuple Any help would be much appreciated

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"sleep" in Haskell
by Michael Mossey 15 Oct '09

15 Oct '09

I can't find a "sleep" function in Haskell. This relates to my wish to use PortMidi and control the timing of actions. Maybe there is another way to do this sort of thing in Haskell. Can anyone help, either with PortMidi or just a general explanation of how IO operations could be placed at certain points in time? Thanks, Mike

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Re: [Haskell-beginners] "sleep" in Haskell
by Michael Mossey 14 Oct '09

14 Oct '09

Hi Philippa, I think you have the right idea, and I want to try that too, but right now I'm using a kind of scattershot approach to try and learn everything I can, both about MIDI and Haskell in general. Since nothing is currently working, getting anything to work would be a learning experience. Thanks, Mike Philippa Cowderoy wrote: > Michael Mossey wrote: >> I can't find a "sleep" function in Haskell. This relates to my wish to >> use PortMidi and control the timing of actions. Maybe there is another >> way to do this sort of thing in Haskell. Can anyone help, either with >> PortMidi or just a general explanation of how IO operations could be >> placed at certain points in time? >> > > Y'know, I can't think of a single language where I'd consider using the > sleep function to time MIDI output. It's normally done with buffered > I/O. I don't know PortMidi, though. >

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Problem to compile an example of Data Parallel Haskell
by Edgar GOMES DE ARAUJO 13 Oct '09

13 Oct '09

Hi, I have tried to compile an example of DPH (Data prallel Haskell) but I am not getting any success. The target is the concmop.hs (http://darcs.haskell.org/ghc-6.10/packages/dph/examples/concomp/) for calculate connected components in a graph. I am using GHC 6.10.4 compiled with extras libs (which also includes DPH 0.3.0). I've got this error. Seems that GHC can't find these functions/types. --------------------------------------------------------------------------------------------------------------------- edgar@edgar-ubuntu:~/Desktop/dph$ ghc --make -fdph-par -XTypeOperators ./concomp.hs [1 of 4] Compiling Graph ( Graph.hs, Graph.o ) Graph.hs:11:45: Not in scope: type constructor or class `:*:' Graph.hs:23:6: Not in scope: `hPutU' Graph.hs:33:15: Not in scope: `hGetU' --------------------------------------------------------------------------------------------------------------------- Using the example from Ben Jao Ming (http://overtag.dk/wordpress/2009/04/data-parallel-haskell/) I can successfully compile and run. Could anyone help me? -- Kind regards, ___________________________________________ *Ir. Edgar Gomes * Metallurgical Engineer /Ghent University/ Department Metallurgy and Materials Science B-9052 Zwijnaarde-Gent Belgium

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Re: Haskell Weekly News: Issue 134 - October 10, 2009
by Benjamin L.Russell 13 Oct '09

13 Oct '09

Either way is fine with me. Since HWN also contains beginner-related topics, personally, I don't think that posting it to Haskell-Beginners takes the group any more off-topic than posting it to Haskell-Cafe (although I can see the argument against cross-posting it to mailing lists in addition to the main Haskell mailing list). If it winds up getting posted to Haskell-Beginners, I'll gladly read it there, but if it just gets posted to the main Haskell mailing list, I'll read it there, also. -- Benjamin L. Russell On Sun, 11 Oct 2009 14:31:22 +0200, Max Rabkin <max.rabkin(a)gmail.com> wrote: >Why don't you subscribe to haskell? It's much lower volume, and I >think it's a better option than taking -beginners off-topic. > >--Max > >On Sun, Oct 11, 2009 at 2:10 PM, Patrick LeBoutillier ><patrick.leboutillier(a)gmail.com> wrote: >> Hi, >> >> Could/should the Haskell Weekly News be posted to the beginners list as >> well? >> >> I normally don't follow haskell-cafe (too much traffic and generally above >> my level I must admit...), but I like to follow what's going on in the >> Haskell community. >> >> >> Patrick -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Re: [Haskell-cafe] Haskell Weekly News: Issue 134 - October 10, 2009
by Patrick LeBoutillier 11 Oct '09

11 Oct '09

Hi, Could/should the Haskell Weekly News be posted to the beginners list as well? I normally don't follow haskell-cafe (too much traffic and generally above my level I must admit...), but I like to follow what's going on in the Haskell community. Patrick On Sat, Oct 10, 2009 at 3:47 AM, <jfredett(a)gmail.com> wrote: > > --------------------------------------------------------------------------- > Haskell Weekly News > http://sequence.complete.org/hwn/20091010 > Issue 134 - October 10, 2009 > --------------------------------------------------------------------------- > Welcome to issue 134 of HWN, a newsletter covering developments in the > [1]Haskell community. > > What with Don Stewart's [2]call to [3]arms to lead Haskell to conquest > over (E)DSL-land, I've once again tried to highlight discussion of > EDSL's this week. Fortunately, it was actually more difficult choosing > what _not_ to include this week, since there was so much discussion > about DSLs and Syntax extensions (a related notion, in my opinion). > Also, this week Bryan O'Sullivan put his Criterion Library to good use > on the `text` package, leading to [4]code which is more than ten times > faster than before! With all this fantastic news, I won't hold you up > any longer, Haskellers, the Haskell Weekly News! > > Announcements > > CfPart: FMICS 2009, 2-3 November 2009, Final Call. FMICS 2009 workshop > chair [5]announced the final call for particpaction for FMICS 2009 > > ICFP videos now available. Wouter Swierstra [6]announced the > availablity of videos from the International Conference on Functional > Programming (ICFP) > > GPipe-1.0.0: A functional graphics API for programmable GPUs. Tobias > Bexelius [7]announced the first release of GPie, a functional graphics > API for programmable GPUs. > > text 0.5, a major revision of the Unicode text library. Bryan > O'Sullivan [8]announced a new, major version of the text package. New > API features, and huge improvments in speed, as Bryan says, 'Get it > while it's fresh on Hackage, folks!' > > vty-ui 0.2. Jonathan Daugherty [9]announced a new version of the vty-ui > package, with fewer bugs, more widgets, and cleaner code due to new > more powerful abstractions. > > htzaar-0.0.1. Tom Hawkins [10]announced HTZAAR, a Haskell > implementation of TZAAR > > Graphalyze-0.8.0.0 and SourceGraph-0.5.5.0. Ivan Lazar Miljenovic > [11]announced To keep this editor happy, Ivan released two new packaged > in one announcement. This time, he's added Legend support to > Graphalyze, but also many new changes to SourceGraph, including a > legend so you can see what all the symbols mean, Better color support, > and much more. > > TxtSushi 0.4.0. Keith Sheppard [12]announced a new version of TxtSushi, > a set of command line utilities for processing CSV and TSV files. > > Discussion > > Applicative do? Philippa Cowderoy [13]asked about a `do` like syntax > for Applicative functors. > > How to add use custom preprocessor in cabal. Bernd Brassel [14]asked > how to add a custom preprocessor to the build chain of a cabal file. > > On DSLs - one last time. Gunther Schmidt [15]summarized his impressions > on al the recent discussion of DSLs > > What is a DSL? Oleg [16]offered some insight into different > [17]properties that can be part of a single tagless framework. He also > pointed to some slides and other materials such as a website [18]here > and slides [19]here about DSL implementations and definitions. > > What is a DSL? Gunther Schmidt [20]posed the question, 'What is a DSL', > and with some further questions added by yours truly, a lively > discussion about the definition of a DSL ensued. > > Finally tagless - stuck with implementation of 'lam'. Gunther Schmidt > [21]asked another question about Finally Tagless DSLs and resolving an > issue with the implementation of 'lam' > > Blog noise > > [22]Haskell news from the [23]blogosphere. Blog posts from people new > to the Haskell community are marked with >>>, be sure to welcome them! > * Darcs: [24]darcs weekly news #43. > * JP Moresmau: [25]What client for an Haskell Multi Player Game?. > * Mikael Vejdemo Johansson (Syzygy-): [26][MATH198] Third lecture is > up. > * Bryan O'Sullivan: [27]Announcing a major revision of the Haskell > text library. > * Eric Kow (kowey): [28]darcs hashed-storage work merged (woo!). > * David Amos: [29]Symmetries of PG(n,Fq). > * The GHC Team: [30]Parallelism /= Concurrency. > * >>> Nefigah: [31]Fake World Haskell. Nefigah, a recent addition to > the community, has been working through RWH, and is providing some > excellent examples. Though, This editor prefers the title 'Real > Life Haskell' as opposed to his choice. > * Tom Schrijvers: [32]Release 0.6 of Monadic Constraint Programming. > * Neil Brown: [33]Concurrency Can Be Deterministic (But The Type > System Doesn't Know It). > * Clint Moore: [34]Curiously Parallel. > * Galois, Inc: [35]Tech Talk: Constructing A Universal Domain for > Reasoning About Haskell Datatypes. > * Neil Brown: [36]Terminal Concurrency: The Printing Process. > * Sean Leather: [37]'Upwards and downwards accumulations on trees' > translated into Haskell. > * Mikael Vejdemo Johansson (Syzygy-): [38][MATH 198] Second lecture. > * Chris Smith: [39]View Patterns as Pattern Matching for Records. > * Chris Smith: [40]Playing With Records. > * FP Lunch: [41]Left Kan extensions of containers. > > Quotes of the Week > > * Baughn: Blum Blum Shub, a PRNG derived from poking around R'Lyeh. > * ksf: * lambdabot locks up ksf in a Monad <ksf> mmmmh it's warm and > fuzzy in here. > * monochrom: Don't wrap your head around Haskell. Immerse! Wrap > Haskell around your head. > * chak: ... In other words, FP is inevitable. > * robreim: I'm in your base hacking all your lambdas > * gwern: RAM is overrated, swap is where it's at ;) > * idnar: [to gwern] swap to a ramdisk! ;P > > About the Haskell Weekly News > > New editions are posted to [42]the Haskell mailing list as well as to > [43]the Haskell Sequence and [44]Planet Haskell. [45]RSS is also > available, and headlines appear on [46]haskell.org. > > To help create new editions of this newsletter, please see the > information on [47]how to contribute. Send stories to jfredett . at . > gmail . dot . com. The darcs repository is available at darcs get > [48]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . > > References > > 1. http://haskell.org/ > 2. > http://www.haskell.org/pipermail/haskell-cafe/2009-October/067203.html > 3. > http://www.reddit.com/r/haskell/comments/9qk54/haskell_should_own_the_edsl_… > 4. > http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… > 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17555 > 6. http://article.gmane.org/gmane.comp.lang.haskell.general/17552 > 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17546 > 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64591 > 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64529 > 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64516 > 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64399 > 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/64301 > 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64616 > 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64558 > 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64552 > 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64533 > 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/ > 18. http://dsl09.blogspot.com/ > 19. http://dsl09.blogspot.com/2009/07/panel.html > 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64474 > 21. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64343 > 22. http://planet.haskell.org/ > 23. http://haskell.org/haskellwiki/Blog_articles > 24. http://blog.darcs.net/2009/10/darcs-weekly-news-43.html > 25. > http://jpmoresmau.blogspot.com/2009/10/what-client-for-haskell-multi-player… > 26. > http://blog.mikael.johanssons.org/archive/2009/10/math198-third-lecture-is-… > 27. > http://www.serpentine.com/blog/2009/10/09/announcing-a-major-revision-of-th… > 28. > http://koweycode.blogspot.com/2009/10/darcs-hashed-storage-work-merged-woo.… > 29. http://haskellformaths.blogspot.com/2009/10/symmetries-of-pgnfq.html > 30. > http://ghcmutterings.wordpress.com/2009/10/06/parallelism-concurrency/ > 31. http://my.life-is-virtual.com/2009/10/07/fake-world-haskell-part-1/ > 32. > http://tomschrijvers.blogspot.com/2009/10/release-06-of-monadic-constraint.… > 33. > http://chplib.wordpress.com/2009/10/07/concurrency-can-be-deterministic/ > 34. http://www.l2mlogistics.com/2009/10/curiously-parallel.html > 35. http://www.galois.com/blog/2009/10/06/huffman-universal/ > 36. http://chplib.wordpress.com/2009/10/06/the-printing-process/ > 37. > http://feedproxy.google.com/~r/splonderzoek/~3/4E8TZPDZ-aM/upwards-and-down…<http://feedproxy.google.com/%7Er/splonderzoek/%7E3/4E8TZPDZ-aM/upwards-and-…> > 38. > http://blog.mikael.johanssons.org/archive/2009/10/math-198-second-lecture/ > 39. > http://cdsmith.wordpress.com/2009/10/04/view-patterns-as-pattern-matching-f… > 40. http://cdsmith.wordpress.com/2009/10/03/playing-with-records/ > 41. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=237 > 42. http://www.haskell.org/mailman/listinfo/haskell > 43. http://sequence.complete.org/ > 44. http://planet.haskell.org/ > 45. http://sequence.complete.org/node/feed > 46. http://haskell.org/ > 47. http://haskell.org/haskellwiki/HWN > 48. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2 > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

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questions about randomness
by Michael Mossey 10 Oct '09

10 Oct '09

I would like to know if this is a good way to do this job, both from the point of view of elegance and efficiency. Maybe it needs to be more strict? I may create lists of 100,000 elements and don't want to run into space/time problems. I want to create an infinite list of Floats (for purposes of lazily zipping or writing later), with the following form: a random number of zeros, followed by a single random non-zero value, repeat the pattern. I call it a "break series" for reasons I won't go into here, but in practice, I want to choose the number of zeros in each section from a range of integers, and I want the non-zero values to have a particular frequency distribution. Here's some code I wrote: import System.Random import Control.Monad import Control.Monad.Random breakSeries :: Rand StdGen [Float] breakSeries = do x <- getRandomR (0.0::Float, 1.0) -- Hacking a simple frequency distribution of values of d. d <- if x < 0.6 then getRandomR (5.0::Float, 8.0) else if x < 0.8 then getRandomR (12.0::Float , 24.0) else getRandomR (60.0::Float , 90.0) n <- getRandomR (4::Int, 6) let bits = replicate n 0.0 ++ [d] liftM (bits++) breakSeries test = print . take 20 . evalRand breakSeries =<< newStdGen

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