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Any way to read in a time?
by David Roundy 19 Oct '02

19 Oct '02

I've been looking at the standard Time module, and it seems pretty easy to convert a date into a string (using either calendarTimeToString or formatCalendarTime), but there doesn't seem to be any way to reverse the process. I understand that there are so many date and time formats that it may be hard to parse, and that for many formats there may be no unambiguous translation back into a CalendarTime (e.g. if the time zone isn't included in the string), but it seems like a pretty fundamental (and commonly needed) ability to be able to output a human-readable date and then read it back in. Does anyone have a suggestion how best to go about this? I guess the easiest way might be to just convert to UTC and then use formatCalendarTime to choose what formatting I want and then write my own parser to reverse the process. But this seems like a process with a relatively high probability of introducing rarely seen bugs, which ought to be dealt with by a standard library. Of course, there are also a couple of other workarounds I could use. CalendarTime derives from Show, so I could just output the result of show, but that's an awfully verbose format. I could also give up on comparing dates (which I don't necesarily need, although it is nice) and just treat dates as strings. Any ideas or commentary would be welcome. -- David Roundy http://civet.berkeley.edu/droundy/

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(no subject)
by Chris.Angus＠Lawson.com 17 Oct '02

17 Oct '02

Does anyone know what happened to the wiki on haskell.org? There was lots of stuff there last year (mostly to do with design patterns) which seems to have been lost. Some of the links are still there but they don't go anywhere. Cheers Chris

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question about lazy io
by David Roundy 12 Oct '02

12 Oct '02

Hello. I have a problem I ran into when I tried writing a function to use lazy IO . Specifically, I would like to be able to compare two directory trees, and I thought the best way to do this would be to compartmentalize things by writing an IO function to read in a whole directory tree (including the contents of its files) in a lazy manner, and then the code to manipulate this tree could be purely functional and non-monadic. The problem is that while reading a file in with readFile (or openFile followed by hGetContents) is lazy regarding the reading of the actual file data, it leaves the file handle open, and (at least on ghc under linux) quickly exhausts the available file handles. I guess this makes sense, since if the file wasn't opened until it was actually used, a file open error couldn't flag an exception at the appropriate time... I think this is a related question to the thread on config files and pure file reading. Certainly if there was a pure functional file read (i.e. readFileOnce), that would solve my problem. I hate to have to write monadic IO code right into the core of my code. The Haskell 98 Library Report describes the state of a file handle after hGetContents as 'semi-closed', meaning it will close as soon as it is finished with the current read. Is there any way to get the file handle into a 'semi-opened' state, in which it will be opened as soon as it starts getting read? That's what I'd really like. fwiw, here's the code I'd like to use to slurp up a directory and its contents: >slurp dirname = do > isdir <- doesDirectoryExist dirname > if isdir > then do > former_dir <- getCurrentDirectory > fnames <- getDirectoryContents dirname > setCurrentDirectory dirname > sl <- slurp_list $ skip_hidden fnames > setCurrentDirectory former_dir > return $ SlurpDir dirname sl > else do > isfile <- doesFileExist dirname > if isfile > then do > contents <- readFile dirname > return $ SlurpFile dirname (lines contents) > else return $ SlurpFile "Oops" [] > >slurp_list :: [FilePath] -> IO [Slurpy] >slurp_list [] = return [] >slurp_list (f:fs) = do > s <- slurp f > ss <- slurp_list fs > return (s:ss) > >skip_hidden :: [FilePath] -> [FilePath] >skip_hidden [] = [] >skip_hidden (('.':_):fps) = skip_hidden fps >skip_hidden (fp:fps) = fp : skip_hidden fps To restate my question (which I may have forgotten to ask...), is there a good way to do this? The only thing that comes to mind is to use unsafeIO, which sounds scary. (Mostly because I don't think I would really understand the consequences.) -- David Roundy http://civet.berkeley.edu/droundy/

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Dealing with configuration data
by Liyang Hu 11 Oct '02

11 Oct '02

Evening, I'm trying to write a utility that reads in some user preferences from a pre-determined file, does some work, and exits. Sounds simple enough. The problem I'm having is with the preferences: How do I make it available throughout the entire program? (FWIW, most of the work is effectively done inside the IO monad.) I could explicitly pass the record around everywhere, but that seems a trifle inelegant. My current solution is to use a global ('scuse my terminology, I'm not sure that's the right word to use here) variable of type IORef Config obtained through unsafePerformIO. It works, but strikes me as a rather barbaric solution to a seemingly tame enough problem... Intuition tells me I should be able to `embed', if you will, the config record somehow within or alongside the IO state, and retrieve it at will. (Is this what MonadState is for?) However it also tells me that this will /probably/ involve lots of needless lifting and rewriting of the existing code, which makes it even less enticing than passing everything around explicitly. Any opinions or suggestions? Cheers, /Liyang -- .--{ Liyang HU }--{ http://nerv.cx/ }--{ Caius@Cam }--{ ICQ: 39391385 }--. | :: zettai unmei mokusiroku :::: absolute destined apocalypse ::::::::: |

8 17

Re: infinite (fractional) precision
by Ashley Yakeley 11 Oct '02

11 Oct '02

At 2002-10-10 01:29, Ketil Z. Malde wrote: >I realize it's probably far from trivial, e.g. comparing two equal >numbers could easily not terminate, and memory exhaustion would >probably arise in many other cases. I considered doing something very like this for real (computable) numbers, but because I couldn't properly make the type an instance of Eq, I left it. Actually it was worse than that. Suppose I'm adding two numbers, both of which are actually 1, but I don't know that: 1.000000000.... + 0.999999999.... The trouble is, as far as I know with a finite number of digits, the answer might be 1.9999999999937425 or it might be 2.0000000000013565 ...so I can't actually generate any digits at all. So I can't even make the type an instance of my Additive class. Not very useful... -- Ashley Yakeley, Seattle WA

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infinite (fractional) precision
by ketil＠ii.uib.no 10 Oct '02

10 Oct '02

Hi I was just browsing around on comp.arch a bit, and there was this discussion about various ways to represent non-integer numeric values. It seems one could easily (I'll get back to that in a moment) calculate the fractional part of numbers lazily, generating the needed precision, and nothing more. Does any such implementation exist in Haskell? I realize it's probably far from trivial, e.g. comparing two equal numbers could easily not terminate, and memory exhaustion would probably arise in many other cases. So, if such implementations exist, how does one deal with these issues? Is it indeed possible to make this useful in practice? (And if it hasn't been implemented, would anybody be interested if I gave it a try?) -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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need help optimizing a function
by David Roundy 10 Oct '02

10 Oct '02

Hello. If you followed my previous post (which was about a bug in my lcs function), this is still the same code (only now bug-free, it seems). It turns out that my lcs diff function is MUCH slower than GNU diff on some test files (much worse than 1000 time slower!).The test case where its speed was close was IO bound on the output to an xterm (silly me). I've profiled my lcs code, and it is spending about 95% of its time in the "hunt_one_char" function. It also claims to spend 0.0% of its time in my_bs, which does a binary search on the array, and is the only other function that gets called by hunt_one_char (not counting itself). I've told the compiler (ghc) to inline hunt_one_char and my_bs to no avail. I guess maybe it can't or won't inline a recursive function, or maybe that just doesn't gain me anything. My only guess is that for some reason it is making an entirely new copy of the array each time it recurses, but that doesn't make any sense, since the array is getting threaded through, so it should be able to just modify the array in place. But then, I'm not entirely clear as to what the compiler can and cannot do as it optimizes. >>data Threshold a = Thresh Int! [a] >> deriving (Show) >> >>hunt_one_char :: String -> [Int] -> Array Int (Threshold String) -> >> Array Int (Threshold String) >>hunt_one_char c [] th = th >>hunt_one_char c (j:js) th = >> case my_bs (Thresh j [c]) th of >> Nothing -> hunt_one_char c js th >> Just k -> >> case th!(k-1) of >> Thresh _ rest -> >> hunt_one_char c js th//[(k,Thresh j (c:rest))] For what it's worth, the calling function is: >>hunt_internal :: [String] -> [[Int]] -> >> Array Int (Threshold String) -> >> Array Int (Threshold String) >>hunt_internal [] _ th = th >>hunt_internal _ [] th = th >>hunt_internal (c:cs) (m:ms) th = >> hunt_internal cs ms $ hunt_one_char c m th Each string in this list of strings is a line from one of the files (and the [[Int]] is a list of line numbers in the other file that that line matches). The array 'th' has size (1,n) where n is the number of lines in the file. My simplest test case consists of a 20k line file, each line of which is unique and a second file which is simply a permutation of the first (moving the first line to the last), so hunt_one_char should be called exactly once for each line, and it is always called with its second argument having exactly one element. In this test case, according to the ghc profiler, 89.7% of the time is spent in hunt_one_char: individual inherited COST CENTRE MODULE entries %time %alloc %time %alloc hunt_internal Main 20001 0.2 0.0 91.4 95.3 hunt_one_char Main 40000 89.7 95.0 91.1 95.3 my_bs Main 20000 0.2 0.0 1.4 0.3 my_helper_bs Main 307231 1.2 0.3 1.2 0.3 This has me at a loss. It seems like such a simple function... of course, it is called 20k times, which could certainly add up, but while each call of my_bs should take O(log 20k) time, each call of hunt_one_char (apart from its one call to my_bs) should only take O(1), so most of the time should be spent in my_bs unless something is terribly wrong (which must be the case here). If it would help, I'd be happy to send a listing of the complete code, but it's 6.5k so I figured it'd be better not to send it, since it seems unlikely that anyone would want to run it anyways. -- David Roundy http://civet.berkeley.edu/droundy/

5 5

Data structure definitions
by Mark T.B. Carroll 09 Oct '02

09 Oct '02

I have a program that basically has, data Expression = Value Value | EVariable Variable | other stuff ... data Value = VNumber Number | other stuff ... data Variable = Variable { variable_name :: String, variable_time :: Expression } data Number = Number { value :: Double, dimension :: Dimension } newtype VariableCount = VariableCount (Variable, Number) The VNumber and EVariable constructors are ugly, though, so I was wondering if I should be using typeclasses - e.g., class Expression a class Expression a => Value a instance Value Number instance Expression Variable ... but I don't see how to define Variable in such a scheme. Maybe I shouldn't be using typeclasses? (Obviously, I actually have lots more type constructors in Expression and Value - dyadic expressions, booleans, etc. - the above with just numbers and variables is somewhat truncated, but should suffice.) -- Mark

3 3

Expander2
by Prof. Dr. Peter Padawitz 08 Oct '02

08 Oct '02

Expander2: A Formal Methods Presenter and Animator ================================================== Expander2 has been designed as a multi-purpose workbench for interactive logical inference, constraint solving, data flow analysis and other procedures building up proofs or computation sequences. Moreover, several interpreters translate expressions into tailor-made two-dimensional representations that range from trees and term graphs to tables, fractals or other turtle-system-generated pictures. Expander2 has been implemented in O'Haskell}, an extension of Haskell with object-oriented features for reactive programming and a typed interface to Tcl/Tk for developing GUIs. Besides a comfortable GUI the design goals of Expander2 were to integrate testing, proving and visualizing deductive methods, to admit several degrees of interaction and to keep the system open for extensions or adaptations of individual components to changing demands. Proofs and computations performed with Expander2 follow the rules and the semantics of swinging types (ls5-www.cs.uni-dortmund.de/~peter/Swinging.html). Swinging types combine constructor-based visible types with state-based hidden types and have unique (Herbrand) models, which interpret relations as the least or greatest solutions of their axioms. All features of the system and their use are described in the manual ls5-www.cs.uni-dortmund.de/~peter/Expander2/Expander2.html (sorry, this is still a big file, it will be splitted soon; PostScript version: ../Expander2/Expander2.ps.gz). The paper ../Expander2/Chiemsee.ps.gz concentrates on the prover features. Download everything with ../Expander2.tar.gz. Please email comments, bugs, etc. to peter.padawitz(a)udo.edu. Peter

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Re: need help optimizing a function
by Zdenek Dvorak 08 Oct '02

08 Oct '02

Hello, > > p.s., I sense your next question is going to be something like "why > > can't the compiler detect that the array can be updated in place > > instead of copied" and the answer, from what i can tell, is simply > > that it doesn't try. > >And one might argue that it should not try [snip] and the other answer is that the result would not be worth the effort usually. The idea seems nice, but the laziness is where I see the problem; see the following code: do_something::Array Int Int->(Array Int Int, Result) do_something a = (a'',res) where a' = a // [(summon_index, summon_int)] w = a' ! 4 res = do_some_work w a'' = a' // [(summon_other_index, summon_other_int)] Seems like nice candidate for update-in-place? But the problem is, that in general you cannot say when w will be evaluated -- so you simply cannot destroy a' before then. This is also reason why DiffArray (from hslibs) does not have to be very useful, unless you have a good control on when things are evaluated -- it may (and it also happened to me) have quadratic behavior in cases like this. To solve this, '!' would have to produce a new array too; but then you must pass it everywhere and effectively you are doing the work monads would do for you. So in general you must choose -- either your programs will be nice and functional, but you will have to use structures with (some kind of) logarithmic slowdown (FiniteMap, Trie), or some of their parts will be embedded in monads. Zdenek Dvorak _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx

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Graphics output
by Gerhard Navratil 08 Oct '02

08 Oct '02

I would like to write line graphics into a file (e.g. contour lines calculated by a Haskell function) and access the data from standard programs. For the output I need a Library. Since I do not to write the output I would like to know if there is a library writing graphics in a standard format like dxf or PostScript. I have not found anything on the Web so this is my last chance. Thanks in advance! Gerhard ==================================== Gerhard Navratil Teaching- And Research-Assistant Vienna University of Technology, Austria Institute for Geoinformation Gusshausstr. 27-29 1040 Vienna Tel.: ++43 (0) 1 / 58 801 - 12721 Fax.: ++43 (0) 1 / 58 801 - 12799 Cel.: ++43 (0) 699 / 197 44 761 http://www.geoinfo.tuwien.ac.at

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how to debug?
by David Roundy 07 Oct '02

07 Oct '02

How does one debug in haskell? I have a function that I could swear should behave differently than it does, and after tracking down bugs for many hours, I'm wondering if there's any way to step through the evaluation of a haskell function? The other way I would be debugging in an imperative language would be to sprinkle printfs around. Is there any way to do something like that cleanly in haskell? The only thing I can think of would be to modify every function to accept an additional parameter, which seems like it's more likely to introduce bugs than remove them... For what it's worth I'm using ghc, and the only debugging options it seems to have are for debugging the compiler itself. I would be happy to install and use hugs for debugging if it has some nicer debugging mode. I have already isolated my bug within one function, but that function has somewhat funky recursion, and uses an array (which I'm none too familiar with in haskell), and there aren't any smaller parts that I can see to test. :( -- David Roundy http://civet.berkeley.edu/droundy/

3 3

Re: how to debug?
by Zdenek Dvorak 06 Oct '02

06 Oct '02

Hello, >How does one debug in haskell? I have a function that I could swear should >behave differently than it does, and after tracking down bugs for many >hours, I'm wondering if there's any way to step through the evaluation of a >haskell function? > >The other way I would be debugging in an imperative language would be to >sprinkle printfs around. Is there any way to do something like that >cleanly in haskell? The only thing I can think of would be to modify every >function to accept an additional parameter, which seems like it's more >likely to introduce bugs than remove them... > >For what it's worth I'm using ghc, and the only debugging options it seems >to have are for debugging the compiler itself. I would be happy to install >and use hugs for debugging if it has some nicer debugging mode. > >I have already isolated my bug within one function, but that function has >somewhat funky recursion, and uses an array (which I'm none too familiar >with in haskell), and there aren't any smaller parts that I can see to >test. :( aside from (useful) general advices already given, just few tips that I found useful when I needed to debug: -- to print debug dumps, you may use 'trace' function from IOExts (but beware, it may affect behavior of your program if used incorrectly) -- other way (safer, but slower to learn and use) is to use Hood library -- if your program fails with some really informative error message of type '*** Exception: Maybe.fromJust: Nothing', compiling it with profiling (-prof -auto-all) and running with +RTS -xc will give you a stack dump (pretty useful, well hidden feature :-) Zdenek Dvorak _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

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Re: how to debug?
by D.Wakeling＠exeter.ac.uk 06 Oct '02

06 Oct '02

David Roundy <droundy(a)jdj5.mit.edu> writes: > How does one debug in haskell? I have a function that I could swear should > behave differently than it does, and after tracking down bugs for many > hours, I'm wondering if there's any way to step through the evaluation of a > haskell function? The best place to start would be with the nhc98 compiler and the Hat tracing system developed by the Functional Programming Group at the University of York. See http://www.cs.york.ac.uk/fp/nhc98 David ------------------------------------------------------------------------------- Dr. David Wakeling, School of Engineering and Computer Science Harrison Building, University of Exeter, Exeter, Devon, EX4 4QF. unofficial web page: http://www.dcs.ex.ac.uk/~dwakelin -------------------------------------------------------------------------------

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Boxed versus Unboxed
by Shawn P. Garbett 03 Oct '02

03 Oct '02

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've been reading on this list about boxed/unboxed structures. I'm not quite clear what this terminology means. Is there a good paper that covers this topic in detail, or a book reference? -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (GNU/Linux) iEYEARECAAYFAj2a8OEACgkQDtpPjAQxZ6DUSgCeIRgAl3dpOPavJhrmwFxal5O1 Y8IAnRDzmdag9lyljlacKtE4aZMujfiG =h2Zn -----END PGP SIGNATURE-----

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Performance question
by ketil＠ii.uib.no 02 Oct '02

02 Oct '02

At the moment, I have a user defined data type on which I have defined some operations, instantiated (not derived) Eq and so on. However, for efficiency I'm storing the actual data in UArrays of Word8. In order for everything to work, I need functions 'toW8' and 'fromW8' to map between the data type and its representation in the array. I gather it is impossible to hide the 'Eq' instance of Word8 and/or redefine it, but could this be circumvented by instead of data Foo = F | G instance Eq Foo where F == _ = True _ == _ = False defining something like newtype Foo = F Word8 f, g, h :: Foo f = F 0 g = F 1 and using the same instance declaration? And will it still fit into a UArray? (It is of course possible that, while profiling indicates otherwise, the conversion functions have little impact in practice; i.e. the optimizer will do away with them.) -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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question about 'sort' algorithm
by David Roundy 02 Oct '02

02 Oct '02

I was wondering if anyone knows what sort of algorithm the 'sort' function in the List module actually uses? In "The Haskell 98 Library Report", they give an insertion sort implementation, but I find it hard to believe that the library actually uses insertion sort. Basically, I need O(n log n) sorting, and this is a bit awkward to accomplish efficiently with lists. I would have thought that this awkwardness should be dealt with in the standard library, but seeing an O(n^2) algorithm in the description troubles me. -- David Roundy http://civet.berkeley.edu/droundy/

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RE: Dealing with configuration data
by Simon Peyton-Jones 26 Sep '02

26 Sep '02

| Sorry, I should also mention implicit parameters, if you're willing to use | that extension. I don't like them, though, and my impression from SPJ is | that it's very unclear whether they will get into Haskell 2 or not... It's *linear* implicit parameters that are a weird beast. Ordinary implicit parameters are quite well behaved. Having said that, there is no Haskell 2 process at the moment... Simon

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Re: Pure File Reading (was: Dealing with configuration data)
by Yoann Padioleau 26 Sep '02

26 Sep '02

Lars Lundgren <d95lars(a)dtek.chalmers.se> writes: > On 26 Sep 2002, Yoann Padioleau wrote: > > > Koen Claessen <koen(a)cs.chalmers.se> writes: > > > > i find your idea very good. > > indeed for the library GetOpt, the argument of a program never change so it > > make sense to make this library without using IO monad, same for argv and for the enviroment. > > > for openFile it seems harder, it would require to have a lock on the file > > to be sure that no one modify the file, same for a webpage. > > > > No, not at all. All that is required is to make sure all calls to openFile > f returns the same string, i.e the contents of the file when it was read > the first time. yes you are right. but it requires to change the name of the function to have Once appended to it. so in the Prelude, we should have 2 version of the same kind of fonction, one pure such as readFileOnce with a cool type, and one such as readFile with an Io type. Sounds good idea to me, cos many programs require just to read a file one time. i dont know if practically it is useful. after all we can do all the IO stuff in the main, and then continue in a pure world. dont know if it is useful to read a file in the middle of a pure function. > > /Lars L > > > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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Re: Pure File Reading (was: Dealing with configuration data)
by Yoann Padioleau 26 Sep '02

26 Sep '02

Koen Claessen <koen(a)cs.chalmers.se> writes: i find your idea very good. indeed for the library GetOpt, the argument of a program never change so it make sense to make this library without using IO monad, same for argv and for the enviroment. for openFile it seems harder, it would require to have a lock on the file to be sure that no one modify the file, same for a webpage. > Dear all, > > At the moment, a discussion on haskell-cafe is going on > about how to neatly program the fact that an entire program > depends on a number of parameters that are read in once at > the beginning of a program. > > The suggestion that many people came up with was using > unsafePerformIO in the beginning to read the file. Here is > my version of that: > > | data Configuration = ... -- config data > | > | getConfig :: Configuration > | getConfig = unsafePerformIO $ > | do ...read configuration from file... > | return configuration > | > | main = > | do doStuff > > It is quite disturbing that there is no other easy way to do > this than using unsafePerformIO (except for using implicit > parameters perhaps, but there are other reasons for not > using those). > > I have been thinking a little bit more about this and here > is what I found. > > Remember the Gofer days, when Gofer had a "function": > > openFile :: FilePath -> String > > This was of course a cheap and dirty way of implementing > things like the getConfig above, but it is impure. However, > one could imagine a functional version of this function: > > readFileOnce :: FilePath -> Maybe String > > This function will read the contents of the file (and return > Nothing if something went wrong), but it is memoized, so > that the second time you use this function you get the same > result. > > So, it is a pure function. (Admittedly, it is somewhat > unpredictable, but you will always get the same result for > the same arguments.) It is no more strange than GHC's pure > version of the getArgs function (I forgot what it was/is > called). > > How about space behavior, you say? Reading a file, and > memoizing the result means storing the whole contents of the > file in memory! > > The point is that the use of this function will typically > happen at the beginning of a program, when reading the > configuration file(s). When all this has happened, the > function readFileOnce, and its memo table, will be garabage > collected. (Of course there is no guarantee that all calls > to readFileOnce will be evaluated at the beginning of a > program, and it is not required, but when you do, there are > no space problems.) > > There could of course be pure "-Once" versions of other IO > operations. Here is a list of possibilities: > > - reading a file > - getting arguments > - getting environment variables > - downloading a webpage > - ... > > What do you think? > > Regards, > /Koen. > > -- > Koen Claessen > http://www.cs.chalmers.se/~koen > Chalmers University, Gothenburg, Sweden. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

2 1

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Kanser tedavisi
by carctol＠yahoo.com 25 Sep '02

25 Sep '02

charset="US-ASCII"; charset="US-ASCII"; charset="US-ASCII"; charset="US-ASCII" Reply-To: carctol(a)yahoo.com Date: Thu, 26 Sep 2002 00:12:08 +0300 X-Priority: 3 X-Library: Indy 9.00.10 X-Mailer: Foxmail Kemoterapinin yan etkileri nedeniyle yorgun ve bitkin d�sm�s bir yakininiz mi var? Yanitiniz evetse vakit kaybetmeyin ve CARCTOL'u denemesini saglayin. Genelde ancak klasik tedavinin ise yaramadiginin anlasilmasi, insanlari baska se�enekler aramaya itmektedir, ancak o durumda maalesef yapacak fazla birsey kalmamaktadir. Ayni hatanin yapilmasina izin vermeyin ve hi�bir yan etkisi olmayan, Himalaya Dagi bitkilerinden �retilen Carctol'u denemesini saglayin. CARCTOL, birka� bin yillik, alternatif Hint Tibbinin (Ayuverda'nin) insanliga sundugu bir umut isigidir. �nceleri v�cudu takviye edici tonik olarak kullanilan bu �r�n simdi yeni form�l�yle kansere karsi etkili bir ila�tir L�tfen asagidaki siteye ugrayin ve Carctol'u yakindan taniyin. http://www.kanser-tedavisi.com esenlikler dileriz.. Listeden adinizin silinmesini istiyorsaniz a_cengiz2002(a)yahoo.com a bos e posta yollayin. Tesekk�rler

1 0

layout problem
by Γιώργος Κοσμίδης 25 Sep '02

25 Sep '02

Thanks for your answer. The lines where as you asnwered me. When I post my mail the layout was tottally ruined. Here I post the program again but I have replaced all spaces with underscores ( _ ) This is the error that I have: ERROR "c:\textanalysis.HS":48 - Syntax error in declaration (unexpected `->') Thanks in advance for all the help that you can give me module Main where import IO import System import List import Maybe import Char import Numeric type Word=String type WordCount=Int type WordTup=(word,wordCount) type WordList=[WordTup] main=do args<-getArgs ________textLines<-getText ________switchArgs args textLines ________where ________switchArgs args textLines ________________________|(isMemberOf "-f" args) && (isMemberOf "-i" args) _________________________=printFreq(sortWordCount(parseLcLine textLines)) ________________________|(isMemberOf "-f" args) _________________________=printFreq(sortWordCount (parseLine textLines)) ________________________|(isMemberOf "-i" args) _________________________=printFreq(sortWordCount (parseLcLine textLines)) ________________________|otherwise _________________________=printFreq(sortName (parseLine textLines)) ________getText::IO String ________getText=do c<-getChar ___________________e<-isEOF ___________________if (e) _______________________then return "" else _______________________(do nc<-getText ___________________________return (:nc)) ________parseLine::String->Wordlist ________parseLine line __________________|(line/="")&&(isWantedChar (headline)) ___________________=fillWordList w(parseLine newLine) __________________|(line/="")&&(not(isWantedChar (headline))) ___________________=parseLine(tail line) ________isMemberOf::String->[String]->Bool ________isMemberOf arg args ___________________=[]/=[a|a<-args,a==arg] ________printFreq::WordList->IO() ________printFreq wl=do sequence (map putWordStat wl) ________________________where ________________________putWordStat(Word,WordCount)->IO() ________________________putWordStat(w,wc) ________________________do putStr w ___________________________putSpc (20 (length w) (length(show wc))) ___________________________putStr (show wc) ___________________________putSpc 8 ___________________________putStr (showFFloat (Just 2) (fromIntegral (wc) * 100.0/fromIntegral (wLength))"") ___________________________putChar '%' ___________________________putChar '\n' ________________________return() ________________________wlLength-countWords wl; ________putSpc::Int->IO() ________putSpc n _______________|n>1 do putChar '' _______________________putSpc (n-1) ________________return() _______________|otherwise=putChar '' ________countWords:Wordlist->Int ________countWords [ ] ________countWords ((w,wc):wl)=wc+countWords wl ________sortName::WordList->WordList ________sortName [ ] = [ ] ________sortName (wn:ws)=sortName [(w,wc) (w,wc) <-ws,not (isGreater (w,wc)wc)] __________________++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc) wn] __________________where __________________isGreater (wl,wcl) (w2,wc2) _____________________________|ord(head(wl))-ord(head(x2))>0=True _____________________________|ord(head(wl))-ord(head(x2))<0=False _____________________________|length wl>l && length w2>l ______________________________=isGreater(tail(wl),wcl) (tail(w2,wc2) _____________________________|otherwise = [] _____________________________where _____________________________w=parseWord line _____________________________newline=drop (length w) line ________parseLcLine::String->WordList ________parseLcLine line ____________________|(line/="") && (isWantedChar (head line))=fillWordList w (parseLcLine newline) ____________________|(line/="") && (not (isWantedChar (head line)))=parseLcLine (tail line) ____________________|otherwise = [] ____________________where ____________________w=map toLower (parseWord line) ____________________newline=drop (lenfth w) line ________parseWord::Word->Word ________parseWord w __________________|(w/="") && (isWantedChar (head w))=(head w): parseWord (tail w)) __________________|otherwise = "" ________isWantedChar::Char->Bool ________isWantedChar c _____________________| (c=='a'|| c=='b'|| c=='c'|| c=='d'|| c=='e'|| c=='f' || c=='g'|| c=='h'|| c=='i'||__c=='j'|| c=='k'|| c=='l'|| c=='m'|| c=='n'|| c=='o'|| c=='p'|| c=='q'|| c=='r'|| c=='s'|| c=='t'|| c=='u'|| c=='v'|| c==' w'|| c=='x'|| c=='y'|| c=='z'||c=='A'|| c=='B'|| c=='C'|| c=='D'|| c=='E'|| c=='F'|| c=='G'|| c=='H'|| c=='I'||__c=='J'|| c=='K'|| c=='L'|| c=='M'|| c== 'N'|| c=='O'|| c=='P'|| c=='Q'|| c=='R'|| c=='S'|| c=='T'|| c=='U'|| c=='V' || c=='W'|| c=='X'|| c=='Y'|| c=='Z'|| = True) _____________________|otherwise = False _______fillWordList::Word->WordList->WordList _______fillWordList w wordlistl ____________________|cWord/= [] =cWord++[wordl,wordCountl)|(wordl,wordCountl<-wordListl,wordl/=w] ____________________|otherwise = (w,l):wordListl ____________________where ____________________cWord=[(wordl,(wordCountl-l)) | (wordl,wordCountl)<-wordListl,wordl==w] __________________________________________________|length w1>1 && length w2==1=True __________________________________________________|otherwise = False ________sortWordCount::WordList->WordList ________sortWordCount [] = [] ________sortWordCount ((wn,wcn):ws=sortWordCount [(w,wc|cw,wc)<-ws,ws<=wvn++ _______________________[(wn,wcn)]++sortWordCount [(cw,wc)|(w,wc)<-ws,wcs,wcn]

4 5

Monad Maybe?
by Russell O'Connor 24 Sep '02

24 Sep '02

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 [To: haskell-cafe(a)haskell.org] Is there a nicer way of writing the following sort of code? case (number g) of Just n -> Just (show n) Nothing -> case (fraction g) of Just n -> Just (show n) Nothing -> case (nimber g) of Just n -> Just ("*"++(show n)) Nothing -> Nothing - -- Russell O'Connor roconnor(a)math.berkeley.edu <http://www.math.berkeley.edu/~roconnor/> ``Any time you skip a commercial [...] you're actually stealing the programming'' -- Jamie Kellner, CEO of TBS -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (SunOS) Comment: For info see http://www.gnupg.org iD8DBQE9jM7juZUa0PWVyWQRAjmlAJ9+YDXUEXEhLTtb2huBZKskJ9JvegCgjPb2 iGb/vYYLK7I+UdfijtEePyQ= =6UZh -----END PGP SIGNATURE-----

8 8

RE: Monad Maybe?
by Simon Marlow 24 Sep '02

24 Sep '02

> I know this has been written about way too much, but I was > wondering what > people thought about using 'liftM f' as opposed to '>>= > return . f'. I > would probably have written Andrew's code using liftM, but I > don't know if > one is necessarily better than the other. Does anyone have strong > thoughts on this? so, using liftM: (number g >>= return . show) becomes (liftM show (number g)) or (show `liftM` number g) but it's important not to get too carried away with abstractions - this example requires a bit of a trawl around the library documentation for someone not familiar with liftM. Personally, unless I was writing fragments like this a lot, I'd just write it as (do r <- number g; return (show r)) Each to his own I suppose. Cheers, Simon

1 0

Re: Problems with IO
by ?????? ????? ????? ?????? 24 Sep '02

24 Sep '02

Now I understand that it's just a lack of knowledge... Sorry for interrupring... By the way, can you recommend a good manual which I can find on the web? -- Zhbanov Pavel

3 4

Problems with IO
by Жбанов Павел Геннад ьевич 24 Sep '02

24 Sep '02

I'm having a problem with writing a function dealing with I/O. Maybe it's just a lack of experience or simple Haskell knowledge because I'm just a beginer. The problem: I want to write a function that converts an IO String into String lala :: IO String -> String Is it possible? If yes, how? -- Жбанов Павел

1 0

question regarding ordering of function definitions
by David Roundy 23 Sep '02

23 Sep '02

Hello all! I've just started learning (and using haskell), and am also using the literate comment mode (latex style), and just ran into a problem that seems like it ought to have a simple solution, which is that it seems that haskell requires you to define all the variations of a function sequentially, which is raining on my literate programming parade. Here is what I'd like to do: \begin{code} data D = A String | B String instance Show D where show = showD instance Read D where readsPrec _ = readsD readD s = (readsA s) ++ (readsB s) \end{code} A is formatted like ``A string''. \begin{code} showD (A s) = "A " ++ s readsA s = [(A thestr, r) | ("A", x) <- mylex s, (thestr, r) <- mylex x] \end{code} B is formatted like ``B string''. \begin{code} showD (B s) = "B " ++ s readsB s = [(B thestr, r) | ("B", x) <- mylex s, (thestr, r) <- mylex x] \end{code} The problem I have is that ghc complains because I've split up the definition of showD with readsA defined in between. This surprised me, since it seemed that the code should still be unambiguous. Is there some nice way around this, or do I have to define a separate function for each constructor, and then have a list in one place (as I do with the readsD, in that case because pattern matching won't give me what I want), like: showD (A s) = showA (A s) showD (B s) = showB (B s) Of course, in my actual example, there are more than two constructors, and the parsing is considerably more complex, which is why I'd like to put the analagous showing and parsing right next to eachother along with a description of what the formatting is intended to be. -- David Roundy http://civet.berkeley.edu/droundy/

3 2

"zipping" two streams in the IO monad
by Nick Name 19 Sep '02

19 Sep '02

How could I "zip" two possibily infinite streams obtained by IO operations, for example to return the infinite list of pairs of values read both from channel a and from channel b with getChanContents? In general, how does one implement a function like "getChanContents" wich returns an infinite list? Tell me just some pointer to information of course, I don't want an entire functional programming lesson :) Vincenzo

2 2

Depth-First search problems
by Dennis Schieferdecker 19 Sep '02

19 Sep '02

Hi! I hope you can help me with this little problem I have: I'm trying to implement a depth-first search on a binary tree from a school book but somehow I always get Haskell error messages (more after the source code). The source is as follows: -- Binary Tree structure data BinTree t = EmptyTree | Bin (BinTree t) t (BinTree t) left (Bin b1 _ _) = b1 right (Bin _ _ b2) = b2 value (Bin _ v _) = v empty EmptyTree = True empty (Bin _ _ _) = False -- Give the Binary Tree == instance Eq a => Eq (BinTree a) where (Bin b v c) == (Bin d w e) = (v == w) && (b == d) && (c == e) EmptyTree == EmptyTree = True EmptyTree == Bin _ _ _ = False -- Stack structure data Keller t = CreateStack | Push (Keller t) t top (Push s x) = x pop (Push s x) = s -- Depth-First search tiefensuche b = fst (until p f ([], Push CreateStack b)) where p(_, k) = empty k f(erg, k) | (top k) == EmptyTree = (erg, pop k) | otherwise = ([v] ++ erg, Push( Push( pop k) b2) b1) where (Bin b1 v b2) = top k The error message says that p has a wrong types Haskell thinks it is p :: (b, BinTree c) -> Bool, instead of p :: ([a], Keller (BinTree a)) -> Bool I really don't know how I can tell to see the right type. Does anyone have an idea what I have to change ? -- ciao dennis "I hear and I forget, I see and I remember, I do and I understand"

2 2

layout problem
by Γιώργος Κοσμίδης 18 Sep '02

18 Sep '02

Hello everyone. I have a problem with a assessment. The problem is with the layout. I cannot understand what is wrong. Here is the code module Main where import IO import System import List import Maybe import Char import Numeric type Word=String type WordCount=Int type WordTup=(word,wordCount) type WordList=[WordTup] main=do args<-getArgs textLines<-getText switchArgs args textLines where switchArgs args textLines |(isMemberOf "-f" args) && (isMemberOf "-i" args) =printFreq(sortWordCount(parseLcLine textLines)) |(isMemberOf "-f" args) =printFreq(sortWordCount (parseLine textLines)) |(isMemberOf "-i" args) =printFreq(sortWordCount (parseLcLine textLines)) |otherwise =printFreq(sortName (parseLine textLines)) getText::IO String getText=do c<-getChar e<-isEOF if (e) then return "" else (do nc<-getText return (:nc)) parseLine::String->Wordlist parseLine line |(line/="")&&(isWantedChar (headline)) =fillWordList w(parseLine newLine) |(line/="")&&(not(isWantedChar (headline))) =parseLine(tail line) isMemberOf::String->[String]->Bool isMemberOf arg args =[]/=[a|a<-args,a==arg] printFreq::WordList->IO() printFreq wl=do sequence (map putWordStat wl) where putWordStat(Word,WordCount)->IO() putWordStat(w,wc) do putStr w putSpc (20 (length w) (length(show wc))) putStr (show wc) putSpc 8 putStr (showFFloat (Just 2) (fromIntegral (wc) * 100.0/fromIntegral (wLength))"") putChar '%' putChar '\n' return() wlLength-countWords wl; putSpc::Int->IO() putSpc n |n>1 do putChar '' putSpc (n-1) return() |otherwise=putChar '' countWords:Wordlist->Int countWords [ ] countWords ((w,wc):wl)=wc+countWords wl sortName::WordList->WordList sortName [ ] = [ ] sortName (wn:ws)=sortName [(w,wc) (w,wc) <-ws,not (isGreater (w,wc)wc)] ++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc) wn] where isGreater (wl,wcl) (w2,wc2) |ord(head(wl))-ord(head(x2))>0=True |ord(head(wl))-ord(head(x2))<0=False |length wl>l && length w2>l =isGreater(tail(wl),wcl) (tail(w2,wc2) |otherwise = [] where w=parseWord line newline=drop (length w) line parseLcLine::String->WordList parseLcLine line |(line/="") && (isWantedChar (head line))=fillWordList w (parseLcLine newline) |(line/="") && (not (isWantedChar (head line)))=parseLcLine (tail line) |otherwise = [] where w=map toLower (parseWord line) newline=drop (lenfth w) line parseWord::Word->Word parseWord w |(w/="") && (isWantedChar (head w))=(head w): parseWord (tail w)) |otherwise = "" isWantedChar::Char->Bool isWantedChar c | (c=='a'|| c=='b'|| c=='c'|| c=='d'|| c=='e'|| c=='f'|| c=='g'|| c=='h'|| c=='i'|| c=='j'|| c=='k'|| c=='l'|| c=='m'|| c=='n'|| c=='o'|| c=='p'|| c=='q'|| c=='r'|| c=='s'|| c=='t'|| c=='u'|| c=='v'|| c=='w'|| c=='x'|| c=='y'|| c=='z'||c=='A'|| c=='B'|| c=='C'|| c=='D'|| c=='E'|| c=='F'|| c=='G'|| c=='H'|| c=='I'|| c=='J'|| c=='K'|| c=='L'|| c=='M'|| c=='N'|| c=='O'|| c=='P'|| c=='Q'|| c=='R'|| c=='S'|| c=='T'|| c=='U'|| c=='V'|| c=='W'|| c=='X'|| c=='Y'|| c=='Z'|| = True) |otherwise = False fillWordList::Word->WordList->WordList fillWordList w wordlistl |cWord/= [] =cWord++[wordl,wordCountl)|(wordl,wordCountl<-wordListl,wordl/=w] |otherwise = (w,l):wordListl where cWord=[(wordl,(wordCountl-l)) | (wordl,wordCountl)<-wordListl,wordl==w] |length w1>1 && length w2==1=True |otherwise = False sortWordCount::WordList->WordList sortWordCount [] = [] sortWordCount ((wn,wcn):ws=sortWordCount [(w,wc|cw,wc)<-ws,ws<=wvn++ [(wn,wcn)]++sortWordCount [(cw,wc)|(w,wc)<-ws,wcs,wcn]

2 1

(no subject)
by Richard Barth 13 Sep '02

13 Sep '02

I'm just learning Haskell with Hugs98. I can't understand why the line defining "foo" is acceptable while the line defining "bar" (only difference is the unary minus) generates the error message at the end. If someone could explain this, or, better yet, tell me how I can figure this out for myself. Thanks. data Entry = Ent {date :: String, amount :: Double} foo = [Ent "baz" 1.0] bar = [Ent "baz" -1.0] Type checking...... ERROR "...test.hs":7 - Unresolved top-level overloading *** Binding : bar *** Outstanding context : Fractional (Double -> Entry)

3 2

Re: (no subject)
by Ashley Yakeley 13 Sep '02

13 Sep '02

At 2002-09-13 12:12, Richard Barth wrote: >I'm just learning Haskell with Hugs98. I can't understand why the line >defining "foo" is acceptable while the line defining "bar" (only >difference is the unary minus) generates the error message at the end. >If someone could explain this, or, better yet, tell me how I can figure >this out for myself. Thanks. > >data Entry = Ent {date :: String, amount :: Double} >foo = [Ent "baz" 1.0] >bar = [Ent "baz" -1.0] Haskell thinks it's a binary minus. Try this: bar = [Ent "baz" (-1.0)] -- Ashley Yakeley, Seattle WA

1 0

maxList
by Nuno Silva 13 Sep '02

13 Sep '02

hello, I'm new to haskell, I'm studying for an exam, and I'm having trouble with this exercise. I have a list of Integers, and I want to return the highest value of all. i have this: comp :: Int -> Int -> Int comp x y | x < y = y | otherwise = x maxList :: [Int] -> [Int] maxList (x1:x2:xs) = comp x1 x2 : maxList xs maxList [] = [] this code returns a list, but I only want it to return a single Int... but can't seem to do it, could you please help me? --------------------------------- Do you Yahoo!? Yahoo! News - Today's headlines

2 1

Make $20,000 with PayPal! Fast, reliable,FREE!!!
by Your Friend 13 Sep '02

13 Sep '02

1 0

Bilgi Payla�t�k�a Artar
by info 10 Sep '02

10 Sep '02

1 0

mutable records
by Scott J. 10 Sep '02

10 Sep '02

Hi, Is it possible to define oject types in Haskell and what does one propose to do it? Is it possible to define parts of a record with the help of the ST s monad mutable during the whole program? (As is possible in Ocamel)? Thx Scott

8 11

RE: A problem with haskell-mode
by Simon Marlow 09 Sep '02

09 Sep '02

> I had the same problem, and I found a fix somewhere. > Don't reember what exactly I had to change so I'll just send > you my Haskell section of xemacs init.el. > > By the way I get an error whenever I type "undefined". Anyone > else noticed it? > (1) (error/warning) Error in `post-command-hook' (setting > hook to nil): > (wrong-type-argument listp a ) I'm officially the maintainer of the emacs Haskell mode since Reuben Thomas left, but I deleted the section of my brain that contained my knowledge of emacs lisp in order to make more room for GHC, so I'm not a very effective maintainer I'm afraid :( Offers to take over the maintainership are entirely welcome, but in the meantime I'm happy to add any fixes for these kinds of problems to the web page and/or the source. Cheers, Simon

1 0

A problem with haskell-mode
by Deling Ren 06 Sep '02

06 Sep '02

Hi, all, I installed the latest version of Haskell mode for emacs. Whenever I load haskell major mode by opening a haskell file, Xemacs gives me the following error message: (1) (error/warning) Error in `post-command-hook' (setting hook to nil): (void-variable imenu--index-alist) My Xemacs version is 21.4.8. It works well under GNU emacs though. Anybody has an idea how to get around it? Thanks. Deling

2 1

aide SVP
by fouad ktiri 30 Aug '02

30 Aug '02

Bonjour, Comment faire pour stocker des données dans une liste comme en programmation normale (x=x+1) Merci beaucoup ______________________________________________________ Boîte aux lettres - Caramail - http://www.caramail.com

2 1

help
by yan zhong 30 Aug '02

30 Aug '02

3 2

RE: Question aboutthe use of an inner forall
by Simon Peyton-Jones 30 Aug '02

30 Aug '02

Now fixed in the 5.04 branch. The fix will get into the HEAD when I merge in the Template Haskell stuff. Thanks for the report Simon | -----Original Message----- | From: Simon Peyton-Jones [mailto:simonpj@microsoft.com] | Sent: 28 August 2002 12:21 | To: Ashley Yakeley | Cc: Haskell Cafe List | Subject: RE: Question aboutthe use of an inner forall | | | No, this is a bug, thank you. Will fix. | | Simon | | | -----Original Message----- | | From: Ashley Yakeley [mailto:ashley@semantic.org] | | Sent: 19 August 2002 11:31 | | To: Jay Cox; Haskell Cafe List | | Subject: Re: Question aboutthe use of an inner forall | | | | | | At 2002-08-18 20:19, Jay Cox wrote: | | | | >#ST> runST (newSTRef (3::Prelude.Int)) | | ># | | >#Ambiguous type variable(s) `a' in the constraint `PrelShow.Show a' | | >#arising from use of `PrelIO.print' at <No locn> #In a 'do' | | expression | | >pattern binding: PrelIO.print it | | | | I don't understand this either, actually: | | | | $ ghci -fglasgow-exts -package lang | | ___ ___ _ | | / _ \ /\ /\/ __(_) | | / /_\// /_/ / / | | GHC Interactive, version 5.04, | | for Haskell | | 98. | | / /_\\/ __ / /___| | http://www.haskell.org/ghc/ | | \____/\/ /_/\____/|_| Type :? for help. | | | | Loading package base ... linking ... done. | | Loading package haskell98 ... linking ... done. | | Loading package lang ... linking ... done. | | Prelude> :module ST | | Prelude ST> :type runST | | | | Inferred type is less polymorphic than expected | | Quantified type variable `s' escapes | | Expected type: ST s a -> t | | Inferred type: (forall s1. ST s1 a) -> a | | Prelude ST> | | | | What's up with that? Can't I even look at the type? Is this the | | monomorphism restriction or something? | | | | -- | | Ashley Yakeley, Seattle WA | | | | _______________________________________________ | | 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 |

2 1

Say�n haskell-cafe ,
by Green Card 29 Aug '02

29 Aug '02

1 0

RE: Question aboutthe use of an inner forall
by Simon Peyton-Jones 28 Aug '02

28 Aug '02

No, this is a bug, thank you. Will fix. Simon | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 19 August 2002 11:31 | To: Jay Cox; Haskell Cafe List | Subject: Re: Question aboutthe use of an inner forall | | | At 2002-08-18 20:19, Jay Cox wrote: | | >#ST> runST (newSTRef (3::Prelude.Int)) | ># | >#Ambiguous type variable(s) `a' in the constraint `PrelShow.Show a' | >#arising from use of `PrelIO.print' at <No locn> #In a 'do' | expression | >pattern binding: PrelIO.print it | | I don't understand this either, actually: | | $ ghci -fglasgow-exts -package lang | ___ ___ _ | / _ \ /\ /\/ __(_) | / /_\// /_/ / / | | GHC Interactive, version 5.04, | for Haskell | 98. | / /_\\/ __ / /___| | http://www.haskell.org/ghc/ | \____/\/ /_/\____/|_| Type :? for help. | | Loading package base ... linking ... done. | Loading package haskell98 ... linking ... done. | Loading package lang ... linking ... done. | Prelude> :module ST | Prelude ST> :type runST | | Inferred type is less polymorphic than expected | Quantified type variable `s' escapes | Expected type: ST s a -> t | Inferred type: (forall s1. ST s1 a) -> a | Prelude ST> | | What's up with that? Can't I even look at the type? Is this the | monomorphism restriction or something? | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe |

1 0

N queens problem
by Jonata Goulart 26 Aug '02

26 Aug '02

This is the problem to figure out the n queens problem but I didn't understand it very well. Somebody can help me ? how legal and queens functions work? attack (l,c) (ll,cc) = l ==ll || (l+c==ll+cc) || (l-c==ll-cc) legal p m = and [not (attack (l,c) (m, length p +1)) | (l,c) <- zip p [1..]] queens n = r n n where r 0 n = [[]] r m n = [p ++ [m] | p <- r (m-1) n, m <-[1..n], legal p m] _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

1 0

Reklam Vermek ��in Servet �demeyin
by info 24 Aug '02

24 Aug '02

Reklam Vermek İçin Servet Ödemeyin · Artık çok daha ucuza ve masrafsız nasıl mı ? · 7 milyon Türk kullanıcısına şirketinizin tanıtımını yaparak · Arama motorlarına kayıt ettirerek · 400.000.000 milyon yabancı kullanıcıya kendinizi tanıtarak Şirket , Kurum , Kuruluş ve Web Sitenizi bu yolla çok daha ucuza tanıtabilirsiniz. - 7 milyon Türk Kullanıcı sadece 49 $ + KDV - 400.000.000 Yabancı Kullanıcı 99 $ + KDV İletişim : Necatibey caddesi 27/11 Sıhhıye – Ankara İcq : 131140541 e-mail : info(a)bulent.net

1 0

Re: Videolar�m - 3
by MERVE＠SEX.COM 23 Aug '02

23 Aug '02

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OT: broken mail threads
by Lauri Alanko 22 Aug '02

22 Aug '02

I'm sorry to bring up such petty issues, but this has been nagging me for quite a long while now... The Haskell mailing lists have one rather unflattering characteristic: their mail threads are almost always broken. I'll elaborate. Most mail user agents arrange messages in threads, keeping track of which message is a reply to which. The programs use the In-Reply-To: and References: -headers of the messages for this. By some coincidence, the various Haskell mailing lists have an uncommonly high proportion of replies which do not have these headers. As a result, many followup messages show up as a new thread in the unlucky reader's mail program, and this makes following a discussion more inconvenient. This also affects web archives of the mailing lists. The reason for these lacking headers is most likely faulty mail programs. Since programs are at fault here, not people, I won't mention names, but will simply identify the most common broken user agents. X-Mailer: Claris Emailer 2.0v3, January 22, 1998 (No threading information of any kind) X-Mimeole: Produced By Microsoft Exchange V6.0.6249.0 (Does have some very non-standard Thread-Topic: and Thread-Index: -headers, but no In-Reply-To: or References:) User-Agent: slrn/0.9.7.4 (Linux) (Apparently via a mail-news -gateway. Replies do have a References: -header, but with locally generated message-ids instead of the real ones.) There are also other messages with threading problems, but these are by far the most common sources. If you find yourself using one of these programs, could you please check your configuration or maybe consider switching to a more well-behaving user agent? This would make your messages much easier to follow. Thanks. Lauri Alanko la(a)iki.fi

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Re: Leical and syntactic analyzer
by Jon Cast 22 Aug '02

22 Aug '02

Jonata Goulart <jonatahh(a)hotmail.com> wrote: > Does somebody know where can I find an example of a lexical and > syntactic analyzer for arithmetic and conditional statements > in Haskell? > Thanks hslibs/hssource in the ghc source (<http://www.haskell.org/ghc/dist/5.04/ghc-5.04-src.tar.bz2>). Jon Cast

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