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Socket Behaviour
by Steinitz, Dominic J 01 Jun '01

01 Jun '01

Apologies if you have received this request for help already. Can anyone tell me why the following code doesn't work as expected? Both the server and client hang. [dom@lhrtba8fd85 simptest]$ server 20000 & [1] 2694 [dom@lhrtba8fd85 simptest]$ client lhrtba8fd85 20000 client: interrupted [1]+ Broken pipe server 20000 [dom@lhrtba8fd85 simptest]$ more log.txt Starting logging Hello world [dom@lhrtba8fd85 simptest]$ So it looks like the hPutStrLn to the server's socket never completes. What's stopping it? On the client side, "Hello world" gets sent but the hGetLine never completes. I guess because the server for some reason can't send. Dominic. module Main(main) where import System import IO import Socket main :: IO () main = do prog <- getProgName args <- getArgs if (length args /= 2) then do putStrLn ("Use: " ++ prog ++ " <host> <port>") exitWith (ExitFailure (-1)) else return () let host = args !! 0 port = read (args !! 1) :: Int in client host (PortNumber (mkPortNumber port)) client :: Hostname -> PortID -> IO () client host port = do sh <- connectTo host port hPutStr sh "Hello world" hFlush sh x <- hGetLine sh putStrLn x module Main (main) where import System import IO import Socket main :: IO () main = do prog <- getProgName args <- getArgs if (length args /= 1) then do putStrLn ("Use: " ++ prog ++ " <port>") exitWith (ExitFailure (-1)) else return () let port = read (args !! 0) :: Int in server (PortNumber (mkPortNumber port)) -- The server function creates a socket to listen on the port and -- loops to log messages. server :: PortID -> IO () server port = do ofh <- openFile "log.txt" WriteMode hPutStrLn ofh "Starting logging" hFlush ofh socket <- listenOn port (sh,host,portid) <- accept socket let loop = do b <- getBuffer sh 16 case b of Full msg -> do hPutStrLn ofh msg hFlush ofh loop Partial msg -> do hPutStrLn ofh msg hFlush ofh hPutStrLn sh "Finishing Logging" hFlush sh hPutStrLn ofh "Finishing logging" hClose ofh in loop data Buffer = Full String | Partial String getBuffer :: Handle -> Int -> IO Buffer getBuffer h n = if (n <= 0) then return (Full "") else do x <- try (hGetChar h) case x of Right c -> do xs <- getBuffer h (n-1) case xs of Full cs -> return (Full (c:cs)) Partial cs -> return (Partial (c:cs)) Left e -> if isEOFError e then return (Partial "") else ioError e ------------------------------------------------------------------------------------------------- 21st century air travel http://www.britishairways.com

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Re: Problem
by Bruno Barbier 01 Jun '01

01 Jun '01

For hugs related questions, you should write at hugs-users(a)haskell.org See also http://haskell.org/mailman/listinfo/ for a list of haskell related mailing lists. For your problem, (works fine with linux, but I guess it's the same for Windows) I do :s to get the search paths and I get | Search path : -P{Hugs}/lib:{Hugs}/lib/hugs:{Hugs}/lib/exts then I type, :s -P{Hugs}/lib:{Hugs}/lib/hugs:{Hugs}/lib/exts:mypath1:mypath2 to add the paths 'mypath1' and 'mypath2' into the search paths; i.e. absolute paths separated by ':' (for Windows, you should probably use ';') Shirley Widyaningsih <coldblue(a)freemail.com.au> writes: > Content-type: text/plain > > > > At 01 Jun 2001 11:18:00 +0200, > Bruno Barbier (barbier(a)comte.univ-fcomte.fr) wrote: > > > > When hugs is not able to find a file, it says this. > > In the interpreter, type ':?' for help, then you can change the > > current > > path or update the paths where hugs looks for files. > > > > > > > > Can you teach me how to change the current path or updates the paths? > when i go to interpreter-> option, this below are appear. > Current settings: +fewuiA -stgl.qQkR -h250000 -p"%s> " -r$$ -c40 > Search path : -P{Hugs}\lib;{Hugs}\lib\hugs;{Hugs}\lib\exts;{Hugs} \lib\win32 > Editor setting : -EC:\WINDOWS\notepad.exe > Preprocessor : -F > > For the information, my hugs directory is in C:\Program Files\HUGS98 > Thank You > > > Sincerely, > > > Shirley > > --------------------------------------------- > WANT A NEW JOB? THEN LET THE JOB FIND YOU > > Visit www.ecruit.com.au and register your > profile. Then the headhunters can find you. > > --------------------------------------------- > Get your own free email account at > http://www.freemail.com.au/ now part of the > Webuser.com.au independent portal. Visit at > http://www.webuser.com.au > --------------------------------------------- -- Bruno Barbier Laboratoire d'Informatique de Besancon, Universite de Franche-Comte, France Phone/Fax : (33) 381.662.087 / (33) 381.666.450 Mailto : barbier(a)lifc.univ-fcomte.fr

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Re: Problem
by Shirley Widyaningsih 01 Jun '01

01 Jun '01

At 01 Jun 2001 11:18:00 +0200, Bruno Barbier (barbier(a)comte.univ-fcomte.fr) wrote: > > When hugs is not able to find a file, it says this. > In the interpreter, type ':?' for help, then you can change the > current > path or update the paths where hugs looks for files. > > > Can you teach me how to change the current path or updates the paths? when i go to interpreter-> option, this below are appear. Current settings: +fewuiA -stgl.qQkR -h250000 -p"%s> " -r$$ -c40 Search path : -P{Hugs}\lib;{Hugs}\lib\hugs;{Hugs}\lib\exts;{Hugs} \lib\win32 Editor setting : -EC:\WINDOWS\notepad.exe Preprocessor : -F For the information, my hugs directory is in C:\Program Files\HUGS98 Thank You Sincerely, Shirley --------------------------------------------- WANT A NEW JOB? THEN LET THE JOB FIND YOU Visit www.ecruit.com.au and register your profile. Then the headhunters can find you. --------------------------------------------- Get your own free email account at http://www.freemail.com.au/ now part of the Webuser.com.au independent portal. Visit at http://www.webuser.com.au ---------------------------------------------

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unfoldr in Library Report
by Ross Paterson 01 Jun '01

01 Jun '01

While looking through the List module, I came across The unfoldr function undoes a foldr operation. Note that, in general, only invertible functions can be unfolded. [followed by an equation about undoing foldr] This is quite inadequate: unfoldr is very useful with non-invertible functions. I suggest something like: The unfoldr function is a `dual' to foldr: while foldr reduces a list to a summary value, unfoldr builds a list from a seed value, e.g., iterate f == unfoldr (\x -> Just (x, f x)) In some cases unfoldr can undo a foldr operation: [followed by the existing equation]

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Problem
by Shirley Widyaningsih 01 Jun '01

01 Jun '01

Dear Sir/Mdm, I've got some problem here, after i install the hugs98, i want to open file "Fact.hs", but there's an error. It's written "ERROR Fact.hs - Unable to open file "Fact.hs" . So what should i do??? Thank you. Sincerely, Shirley --------------------------------------------- WANT A NEW JOB? THEN LET THE JOB FIND YOU Visit www.ecruit.com.au and register your profile. Then the headhunters can find you. --------------------------------------------- Get your own free email account at http://www.freemail.com.au/ now part of the Webuser.com.au independent portal. Visit at http://www.webuser.com.au ---------------------------------------------

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Information
by Shirley Widyaningsih 31 May '01

31 May '01

Dear Sir/Mdm, I would like to ask some information about Haskell. For the information, I'm a student that currently studying at Bina Nusantara University, Jakarta, Indonesia and taking computer science as my subject. In Indonesia, we've never learned about Haskell. It's not populer in Indonesia, many people don't know about it. I know it from my friend that studying in Sydney, Australia. I would to install/download this program, could you give me some info where i can get this software ? If i have to but the software, what is the software name ? Is it haskell too?? Thank you. Sincerely, Shirley --------------------------------------------- WANT A NEW JOB? THEN LET THE JOB FIND YOU Visit www.ecruit.com.au and register your profile. Then the headhunters can find you. --------------------------------------------- Get your own free email account at http://www.freemail.com.au/ now part of the Webuser.com.au independent portal. Visit at http://www.webuser.com.au ---------------------------------------------

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RE: Haskell 98 Report
by Simon Peyton-Jones 31 May '01

31 May '01

| > | deleteBy :: (a -> b -> Bool) -> a -> [b] -> [b] | > | | > | I've found it usefully used at this more general type. | > | > Indeed, and | > | > deleteFirstsBy :: (a -> b -> Bool) -> [b] -> [a] -> [b] | | and | | intersectBy :: (a -> b -> Bool) -> [a] -> [b] -> [a] Indeed. We should either generalise all three deleteBy deleteFirstsBy intersectBy or none. In favour: the more general types are occasionally useful no programs stop working Against it's an unforced change perhaps some error message may get more obscure Tom wrote | That suggests a reason to leave the type of intersectBy alone | - the generalisation would arbitrarily favour the first | list's type over the second list's type. To me, the word | "intersect" implies symmetry. The point is that you can always use it at the symmetrical type too. This isn't a big issue, or I would not be considering it at this point. So I solicit feedback, and will then just decide something. Simon

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Re: Haskell 98 Report
by C.Reinke 31 May '01

31 May '01

"..it's easy enough for programmers who want a generalized version to just cut and paste the code from the Haskell report and give it a more general type signature,.." Fergus Henderson, June 2001 Is this definition of reuse in Haskell quotable?-) Claus

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Re: Dividing Floats
by Daniel Russell 31 May '01

31 May '01

> Can anyone please help me. > How can you divide two floats? (and return a float, even if they divide > equally) > Ie (something like...) div 2.4 1.2 ---> 2.0 The above doesn't work since div can only be applied to integral numbers: div :: Integral a => a -> a -> a What you need is the operator (/) which can only be applied to fractional numbers: (/) :: Fractional a => a -> a -> a For example: 2.4 / 1.2 ---> 2.0 or (/) 2.4 1.2 ---> 2.0 Dan Russell Kingston University

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Dividing floats
by Joshua Ginges 31 May '01

31 May '01

Can anyone please help me. How can you divide two floats? (and return a float, even if they divide equally) Ie (something like...) div 2.4 1.2 ---> 2.0 Thanks Josh

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