- Glasgow-haskell-users

RE: Seq ??
by Julian Seward (Intl Vendor) 04 Jun '01

04 Jun '01

| > In ghc-5.00.1, "seq (2/0) 3" gives 3. Should it not give | error. Hugs does. | | I suspect that Hugs is wrong and ghc is right in this case. | Certainly nhc98 and hbc agree with ghc's behaviour. | | seq x y means evaluate x to whnf and throw away the result, | returning y instead. It shouldn't matter whether the result | of x is bottom. This doesn't seem a correct explaination to me. seq _|_ anything == _|_ The reason that it doesn't bomb in GHCi, and I presume nhc98 and hbc is because the type of (2/0) is Fractional a => a, which is defaulted to Double. However, 2/0 :: Double is a well defined value -- an IEEE754 Infinity (try it)! I think what Saswat expected to see can be made to happen if you force the division to be an integer division: Prelude> seq (2 `div` 0) 3 Floating point exception cam-02-unx:~$ J

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Seq ??
by Saswat Anand 04 Jun '01

04 Jun '01

In ghc-5.00.1, "seq (2/0) 3" gives 3. Should it not give error. Hugs does. Thanks, S

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RE: Instance Declaration discrepancy
by Simon Peyton-Jones 04 Jun '01

04 Jun '01

You need -fallow-undecidable-instances as well. Simon | -----Original Message----- | From: Saswat Anand [mailto:iscp9157@nus.edu.sg] | Sent: 02 June 2001 10:13 | To: 'glasgow-haskell-users(a)haskell.org' | Subject: Instance Declaration discrepancy | | | | class MyShow a where | sh :: a -> String | | instance (Integral a) => Show a where | sh = "Integer " + show a | | Ghc 5.00.1 (with -fglasgow-exts) does not accept the above, | while hugs with extensions has no problem with this. Is it a bug? | | Thanks, | S | | | | | | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-| haskell-users |

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Re: Instance Declaration discrepancy
by Saswat Anand 02 Jun '01

02 Jun '01

> I am sorry for the typos. It should have been > > instance (Integral a) => Show a where > sh a = "Integer " ++ (show a) > > > > class MyShow a where > sh :: a -> String > > instance (Integral a) => Show a where > sh = "Integer " + show a > > Ghc 5.00.1 (with -fglasgow-exts) does not accept the above, while hugs > with extensions has no problem with this. Is it a bug? > > Thanks, > S > > > > >

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Instance Declaration discrepancy
by Saswat Anand 02 Jun '01

02 Jun '01

class MyShow a where sh :: a -> String instance (Integral a) => Show a where sh = "Integer " + show a Ghc 5.00.1 (with -fglasgow-exts) does not accept the above, while hugs with extensions has no problem with this. Is it a bug? Thanks, S

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Weak pointers, garbage collection & deadlocks
by Manuel M. T. Chakravarty 02 Jun '01

02 Jun '01

While using weak pointers and concurrency together, I became convinced that before issuing the ``no threads to run: infinite loop or deadlock?'' error message, the RTS should perform a GC. The reason is that the GC may run some finalisers, which in turn may unlock some threads. The concrete scenario that I have is that I use a finaliser to close a stream when the handle that provides input to that stream dies. Now if the only other thread is a consumer of that stream that waits for it to close, then this thread can't run before the next GC is performed and runs the finaliser. Opinions? Cheers, Manuel

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Socket Behaviour
by Steinitz, Dominic J 31 May '01

31 May '01

Can anyone tell me why the following code doesn't work as expected? Both the server and client hang. If I run server 20000 & and client <hostname> 20000 the server logfile produces [dom@lhrtba8fd85 twotest]$ more log.txt Thu May 31 14:35:39 BST 2001 Starting logging Thu May 31 14:36:08 BST 2001 Hello world 48 65 6c 6c 6f 20 77 6f 72 6c 64 so it looks like the hPutStrLn to the socket never completes. On the client side, "Hello world" gets sent but the hGetLine never completes. Client do sh <- connectTo host port hPutStr sh "Hello world" hFlush sh x <- hGetLine sh putStrLn x Server socket <- listenOn port (sh,host,portid) <- accept socket let loop = do b <- getBuffer sh 16 case b of Full msg -> do logMessage ofh (hexedMessage msg) loop Partial msg -> do logMessage ofh (hexedMessage msg) hPutStrLn sh "Finishing Logging" hFlush sh logMessage ofh "Finishing logging" hClose ofh in loop Dominic. Here's the full code: module Main (main) where import System import IO import Time import Socket import Char 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 logMessage ofh "Starting logging" socket <- listenOn port (sh,host,portid) <- accept socket let loop = do b <- getBuffer sh 16 case b of Full msg -> do logMessage ofh (hexedMessage msg) loop Partial msg -> do logMessage ofh (hexedMessage msg) hPutStrLn sh "Finishing Logging" hFlush sh logMessage 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 logMessage :: Handle -> String -> IO () logMessage hd msg = do clock <- getClockTime calendar <- toCalendarTime clock hPutStrLn hd ((calendarTimeToString calendar) ++ "\n" ++ msg) hFlush hd showHex :: Char -> String showHex x = let y = ord x in hexDigit (y `div` 16):hexDigit (y `mod` 16):[] hexDigit :: Int -> Char hexDigit x | (0 <= x) && (x <= 9) = chr(ord '0' + x) | (10 <= x) && (x <=16) = chr(ord 'a' + (x-10)) | otherwise = error "Outside hexadecimal range" hexedMessage :: String -> String hexedMessage msg = (map toPrint msg) ++ " " ++ unwords (map showHex msg) toPrint :: Char -> Char toPrint x = if ((isAscii x) && (not (isControl x))) then x else '.' 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 ------------------------------------------------------------------------------------------------- 21st century air travel http://www.britishairways.com

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RE: extending --make
by Simon Marlow 31 May '01

31 May '01

> I have a whish for the GHC `making' possibilities. > > ghc-5* -package-name --make > > is said trying to replace Makefile. But it is half-successful. > * First, it needs -ohi option working > (to move .hi -s to chosen directory). I've added a -hidir option which should do the right thing. > * Second, could GHC provide options for creating libraries, > adding to library? This might make it easier to build a library from Haskell files, but it would also be duplicating functionality that is already available. I don't see it as a priority, I'm afraid. > Explanation. > With ghc-4, I used Makefile and -odir, -ohi options to provide > the project installation. > Makefile contained > (1) > the project directory tree description, > variables holding the list of names for the .hs, .hi, .o files, > rules to convert .hs --> .o, and such. > Also it contained the library creation part: > (2) > foo: $(objectFiles) > ar -q export/libHSfoo.a `ls export/*.o` > ranlib export/libHSfoo.a > rm -f `ls export/*.o` So you can use the same makefile, but you can replace part (1) with a single rule which uses --make. Cheers, Simon

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RE: package for ghci
by Simon Marlow 31 May '01

31 May '01

> The user (myself) thinks at this: > "HSmypkg" in package specification --> <prefix?>HSmypkg.a > <prefix?>HSmypkg.o > in the library directory. I've clarified this in the documentation, thanks for the comments. Cheers, Simon

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extending --make
by S.D.Mechveliani 31 May '01

31 May '01

Hello, I have a whish for the GHC `making' possibilities. ghc-5* -package-name --make is said trying to replace Makefile. But it is half-successful. * First, it needs -ohi option working (to move .hi -s to chosen directory). * Second, could GHC provide options for creating libraries, adding to library? Explanation. With ghc-4, I used Makefile and -odir, -ohi options to provide the project installation. Makefile contained (1) the project directory tree description, variables holding the list of names for the .hs, .hi, .o files, rules to convert .hs --> .o, and such. Also it contained the library creation part: (2) foo: $(objectFiles) ar -q export/libHSfoo.a `ls export/*.o` ranlib export/libHSfoo.a rm -f `ls export/*.o` ------------------- Now, with ghc-5, I apply ghc -package-name foo -odir export ... --make .. The part (1) cancels due to --make. Further, as ghc-5 observes in the package specification library_dirs = [".../export"] hs_libraries = ["libHSfoo"], then, it can understand what library file is to be created - on demand. If ghc -c provided also the options like -addto-lib -a, -addto-lib -o, ... then it could `make' for the given package _with_ adding to library. So, GHC would be able to simplify Makefile to package setting. The matter is that Makefile has a strange language, far from Haskell. Also why the Haskell user has to study library creation with `ar', `ranlib, `ld'? This, and Makefile look rather like a system hackering. Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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