October 2011 - Haskell-Cafe

Question on `runState'
by Captain Freako 17 Oct '11

17 Oct '11

In this excerpt from the `StateArrow' page: runState :: Arrow<http://hackage.haskell.org/packages/archive/base/4.2.0.2/doc/html/Control-A…>a => StateArrow<http://hackage.haskell.org/packages/archive/arrows/0.4.1.2/doc/html/Control…>s a *e* b -> a (e, s) (b, s)Source<http://hackage.haskell.org/packages/archive/arrows/0.4.1.2/doc/html/src/Con…> what's the significance of having written "StateArrow s a *e* b", instead of "StateArrow s a b c"? Thanks, -db

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Re: [Haskell-cafe] parser error in pattern
by Ivan Lazar Miljenovic 17 Oct '11

17 Oct '11

On 18 October 2011 09:14, kolli kolli <nammukolli04(a)gmail.com> wrote: > I didnt understand properly but made changes according to what I > understood..Its still giving me the same error > > eval1(If t1 t2 t3) = case (If t1 t2 t3) of > eval1(If t1 t2 t3) -> Just t1 You can't do that.... if you want the result to be "Just t1", why not just have "eval1 (If t1 t2 t3) = Just t1", with no case or where statement? > > > On Mon, Oct 17, 2011 at 4:10 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> >> On 18 October 2011 09:08, kolli kolli <nammukolli04(a)gmail.com> wrote: >> > actual error message is >> > >> > homework2.lhs:137:20: parse error on input `where' >> > >> > data Term = Tru >> > | Fls >> > | If Term Term Term >> > | Zero >> > | Succ Term >> > | Pred Term >> > | IsZero Term >> > deriving Eq >> > >> >> As I said, the error is from your incorrect usage of the case >> statement; it _should_ look something like: >> >> case foo of >> bar -> baz >> bar' -> baz' >> >> > >> > >> > >> > >> > On Mon, Oct 17, 2011 at 4:03 PM, Ivan Lazar Miljenovic >> > <ivan.miljenovic(a)gmail.com> wrote: >> >> >> >> On 18 October 2011 08:56, kolli kolli <nammukolli04(a)gmail.com> wrote: >> >> > after parsing a string i am evaluating it... >> >> > string if t1 then t2 else t3 >> >> > my code is >> >> > eval1 :: Term -> Maybe Term >> >> > eval1(If Tru t2 t3) = Just t2 >> >> > eval1(If Fls t2 t3) = Just t3 >> >> > eval1(If t1 t2 t3) = case eval t1 >> >> > where eval1(If t1 t2 t3) = Just t1 >> >> > >> >> > eval :: Term -> Term >> >> > eval (IsZero Zero) = Tru >> >> > eval (Zero) = Zero >> >> > eval(Pred Zero) = Pred Zero >> >> >> >> Your case statement is incomplete for starters... >> >> >> >> Can you please provide the actual error message as well? Your >> >> definition of Term would also be useful. >> >> >> >> > >> >> > On Mon, Oct 17, 2011 at 3:46 PM, Ivan Lazar Miljenovic >> >> > <ivan.miljenovic(a)gmail.com> wrote: >> >> >> >> >> >> On 18 October 2011 08:43, kolli kolli <nammukolli04(a)gmail.com> >> >> >> wrote: >> >> >> > hey can anyone tell me what is parser error in parser??Plz help me >> >> >> > out >> >> >> >> >> >> It's when the parser can't parse what it's provided.... providing >> >> >> the >> >> >> code that caused the problem and the actual error message is >> >> >> required >> >> >> for a more detailed explanation. >> >> >> >> >> >> -- >> >> >> Ivan Lazar Miljenovic >> >> >> Ivan.Miljenovic(a)gmail.com >> >> >> IvanMiljenovic.wordpress.com >> >> > >> >> > >> >> >> >> >> >> >> >> -- >> >> Ivan Lazar Miljenovic >> >> Ivan.Miljenovic(a)gmail.com >> >> IvanMiljenovic.wordpress.com >> > >> > >> >> >> >> -- >> Ivan Lazar Miljenovic >> Ivan.Miljenovic(a)gmail.com >> IvanMiljenovic.wordpress.com > > -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Re: [Haskell-cafe] parser error in pattern
by Ivan Lazar Miljenovic 17 Oct '11

17 Oct '11

On 18 October 2011 09:08, kolli kolli <nammukolli04(a)gmail.com> wrote: > actual error message is > > homework2.lhs:137:20: parse error on input `where' > > data Term = Tru > | Fls > | If Term Term Term > | Zero > | Succ Term > | Pred Term > | IsZero Term > deriving Eq > As I said, the error is from your incorrect usage of the case statement; it _should_ look something like: case foo of bar -> baz bar' -> baz' > > > > > On Mon, Oct 17, 2011 at 4:03 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> >> On 18 October 2011 08:56, kolli kolli <nammukolli04(a)gmail.com> wrote: >> > after parsing a string i am evaluating it... >> > string if t1 then t2 else t3 >> > my code is >> > eval1 :: Term -> Maybe Term >> > eval1(If Tru t2 t3) = Just t2 >> > eval1(If Fls t2 t3) = Just t3 >> > eval1(If t1 t2 t3) = case eval t1 >> > where eval1(If t1 t2 t3) = Just t1 >> > >> > eval :: Term -> Term >> > eval (IsZero Zero) = Tru >> > eval (Zero) = Zero >> > eval(Pred Zero) = Pred Zero >> >> Your case statement is incomplete for starters... >> >> Can you please provide the actual error message as well? Your >> definition of Term would also be useful. >> >> > >> > On Mon, Oct 17, 2011 at 3:46 PM, Ivan Lazar Miljenovic >> > <ivan.miljenovic(a)gmail.com> wrote: >> >> >> >> On 18 October 2011 08:43, kolli kolli <nammukolli04(a)gmail.com> wrote: >> >> > hey can anyone tell me what is parser error in parser??Plz help me >> >> > out >> >> >> >> It's when the parser can't parse what it's provided.... providing the >> >> code that caused the problem and the actual error message is required >> >> for a more detailed explanation. >> >> >> >> -- >> >> Ivan Lazar Miljenovic >> >> Ivan.Miljenovic(a)gmail.com >> >> IvanMiljenovic.wordpress.com >> > >> > >> >> >> >> -- >> Ivan Lazar Miljenovic >> Ivan.Miljenovic(a)gmail.com >> IvanMiljenovic.wordpress.com > > -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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parser error in pattern
by kolli kolli 17 Oct '11

17 Oct '11

hey can anyone tell me what is parser error in parser??Plz help me out

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ANN: netwire 1.2.7
by Ertugrul Soeylemez 17 Oct '11

17 Oct '11

Hello fellows, netwire 1.2.7 is out. Summary of the changes from netwire 1.2.5 (my last announcement): * Events: Added 'periodically' event generator. * Manager: Added the 'manager' wire, which is sort of a generalization of the various context wires and should be useful for highly dynamic applications like games. * FRP.NetWire now also exports mkGen, toGen and the WireState type. Furthermore I have added mkFix to ease writing stateless wires. Right now this just translates to mkGen, but might make use of a special Wire constructor in the future. * Added appFirst, appFrozen, appEvent and an ArrowApply instance based on appFrozen. All these allow you to embed a wire network into the running network. The embedded network is allowed to be a signal itself, which technically turns Wire into a monad. * Added testWire and testWireStr to ease writing wire test programs. * The FRP.NetWire.Concurrent module is gone for now. I'm performing a lot of research regarding embedded concurrent wire sessions, but I have not reached a point where I can provide a stable implementation yet. * Lots of documentation improvements. Please keep the feedback coming. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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Fwd: how to increase the stack size
by kolli kolli 17 Oct '11

17 Oct '11

when I am running the program in my terminal on ubuntu its showing me GHC stack-space overflow: current limit is 536870912 bytes. Use the `-K<size>' option to increase it. how can i increase the stack size????Plz help me out....

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Correction: subclasses and classes with same type in instance
by Patrick Browne 16 Oct '11

16 Oct '11

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How to wrap a StateArrow in an Automaton?
by Captain Freako 16 Oct '11

16 Oct '11

HI all, How do you wrap a StateArrow in an Automaton? Thanks, -db

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Question, re: using Automaton
by Captain Freako 16 Oct '11

16 Oct '11

Hi all, In this excerpt from the Automaton<http://hackage.haskell.org/packages/archive/arrows/0.4.1.2/doc/html/Control…>page: runAutomaton :: (ArrowLoopC<http://hackage.haskell.org/packages/archive/base/4.2.0.2/doc/html/Control-A…>a, ArrowApply<http://hackage.haskell.org/packages/archive/base/4.2.0.2/doc/html/Control-A…>a) => Automaton<http://hackage.haskell.org/packages/archive/arrows/0.4.1.2/doc/html/Control…>a (e, b) c -> a (e, Stream<http://hackage.haskell.org/packages/archive/Stream/0.4.1/doc/html/Data-Stre…>b) ( Stream<http://hackage.haskell.org/packages/archive/Stream/0.4.1/doc/html/Data-Stre…>c) Source<http://hackage.haskell.org/packages/archive/arrows/0.4.1.2/doc/html/src/Con…> Encapsulating an automaton by running it on a stream of inputs, obtaining a stream of outputs. Typical usage in arrow notation: proc p -> do ...* ys <- (|runAutomaton (\x -> ...)|) xs* Here xs refers to the input stream and x to individual elements of that stream. ys is bound to the output stream. Could someone replace the ellipses w/ an expression that would compile and make sense? (I'm really struggling, trying to understand this example.) Thanks! -db

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Reading pcap file
by mukesh tiwari 16 Oct '11

16 Oct '11

Hello everyone I am writing application which reads pcap file like wireshark in pure haskell but there is some thing missing. I read this file http://www.viste.com/Linux/Server/WireShark/libpcapformat.pdf<http://www.google.com/url?sa=D&q=http://www.viste.com/Linux/Server/WireShar…> and it say that first 24 bytes are global headers , after that every packet contains pcap local header and data. What i am trying to do is , first trying to get the bytes of data in each packet by reading the third field incl_len in local header but my code is not behaving as it suppose . I am not getting the list of parsed packets . My test libcap file is http://wiki.wireshark.org/SampleCaptures?action=AttachFile&do=view&ta...<http://www.google.com/url?sa=D&q=http://wiki.wireshark.org/SampleCaptures%3…> --http://www.viste.com/Linux/Server/WireShark/libpcapformat.pdf<http://www.google.com/url?sa=D&q=http://www.viste.com/Linux/Server/WireShar…> --http://hackage.haskell.org/packages/archive/bytestring/0.9.0.4/doc/<http://www.google.com/url?sa=D&q=http://hackage.haskell.org/packages/archiv…> html/Data-ByteString-Lazy.html import Data.List import qualified Data.ByteString.Lazy as BS import qualified Data.ByteString.Lazy.Char8 as B import Control.Monad import Text.Printf import Data.Word import Data.Char import System.Time import Numeric import System.Environment hexTodec :: BS.ByteString -> Integer hexTodec lst = read $ "0x" ++ ( concatMap ( \x -> showHex x "" ) $ BS.unpack lst ) parseFile :: BS.ByteString -> Bool -> IO [ BS.ByteString ] parseFile xs revflag | BS.null xs = return [] | otherwise = do let ind =if revflag then hexTodec . BS.reverse . BS.take 4 . BS.drop 8 $ xs else hexTodec . BS.take 4 . BS.drop 8 $ xs print ind let ( x , ys ) = BS.splitAt ( fromIntegral ind ) xs --BS.putStrLn $ x tmp <- parseFile ys revflag return $ x : tmp main = do [ file ] <- getArgs contents <- BS.readFile file let ( a , rest ) = BS.splitAt 24 contents --strip global header let revflag = case BS.unpack $ BS.take 4 a of [ 0xd4 , 0xc3 , 0xb2 , 0xa1 ] -> True _ -> False p <- parseFile rest revflag print $ p !! 0 BS.putStr $ p !! 0 Regards Mukesh Tiwari

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