April 2003 - Glasgow-haskell-users

bug in Handle.hs!!!
by Keean Schupke 09 Apr '03

09 Apr '03

seeing as nobody replied to this i'll send it again ... I think its important these problems get fixed! Here are the symptoms, each connection to a server sparks a thread. The thread does the processing, which may be interrupted by an asynchnonous exception (sigPIPE) at any point. Sometimes partially closed sockets are left open, even though the sparked thread has a finally clause closeing the handle for the socket. This seems to happen because a write to a socket that has been closed at the write end causes sigPIPE. If this signal is ignored an asynchronous exception is delivered to the thread, which causes a thread level exception handler to try and close the socket. The problem seems to be the finalizer itself tries to flush the write side, which results in an uncought exception meaning c_close is never called, hence the hanging socket. Here is a possible fix: handleFinalizer :: MVar Handle__ -> IO () handleFinalizer m = do h_ <- takeMVar m catch (flushWriteBufferOnly h_) (\e -> return()) -- catch exception if remote side closed let fd = fromIntegral (haFD h_) unlockFile fd when (fd /= -1) #ifdef mingw32_TARGET_OS (closeFd (haIsStream h_) fd >> return ()) #else (c_close fd >> return ()) #endif return () I think hClose should be modified also, does this sound reasonable? Regards, Keean Schupke

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RE: Type Inference Infelicity
by Simon Peyton-Jones 08 Apr '03

08 Apr '03

Interesting example, right on the borderline. I've jiggled the type inference for applications a bit so that it works (HEAD only of course). Thanks for the test case. Simon | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 19 March 2003 09:43 | To: glasgow-haskell-users(a)haskell.org | | This should compile, shouldn't it? | | -- ghc -c -fglasgow-exts TestInfer.hs | module TestInfer where | { | class C t a b | t a -> b; | instance C Char a Bool; | | data P t a = forall b. (C t a b) => MkP b; | | data Q t = MkQ (forall a. P t a); | | f' :: Q Char; | f' = MkQ (MkP True :: forall a. P Char a); | | f :: Q Char; | f = MkQ (MkP True); | } | | GHC 5.04.2 for MacOS X complains about f, but not about f': | | TestInfer.hs:15: | Could not deduce (C t a Bool) from the context () | Probable fix: | Add (C t a Bool) to the When generalising the type of an | expression | Or add an instance declaration for (C t a Bool) | arising from use of `MkP' at TestInfer.hs:15 | In the first argument of `MkQ', namely `(MkP True)' | In the definition of `f': MkQ (MkP True) | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | 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: ghc puzzling behaviour
by Simon Peyton-Jones 08 Apr '03

08 Apr '03

Thank you. A palpable bug. Fixed. Simon | -----Original Message----- | From: glasgow-haskell-users-admin(a)haskell.org [mailto:glasgow-haskell-users- | admin(a)haskell.org] On Behalf Of Ketil Z. Malde | Sent: 07 April 2003 13:33 | To: glasgow-haskell-users(a)haskell.org | | | Hi, | | When compiling with -funbox-strict-fields, the supplied code doesn't | seem to compile, requiring 'Ord Foo' to derive 'Ord Zot', even if 'Ord | Bar' is explicitly declared. Without the flag, it works as expected. | | Is this intentional? I'll get by by dropping -funbox, or explicitly | declaring the instance, so it's no big deal -- just slightly | surprising. | | --T1.hs-- | | > module T1 where | > | > data Foo = Foo Int String | > data Bar = Bar Int Foo | > | > instance Ord Bar where | > compare (Bar i _) (Bar j _) = compare i j | > | > instance Eq Bar where | > (Bar i _) == (Bar j _) = i == j | | --T2.hs-- | | > module Main where | > | > import T1 | > | > data Zot = Zot !Bar !String deriving (Ord,Eq) | > | > main = putStrLn "Success" | | -kzm | -- | If I haven't seen further, it is by standing in the footprints of giants | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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ghc puzzling behaviour
by ketil＠ii.uib.no 07 Apr '03

07 Apr '03

Hi, When compiling with -funbox-strict-fields, the supplied code doesn't seem to compile, requiring 'Ord Foo' to derive 'Ord Zot', even if 'Ord Bar' is explicitly declared. Without the flag, it works as expected. Is this intentional? I'll get by by dropping -funbox, or explicitly declaring the instance, so it's no big deal -- just slightly surprising. --T1.hs-- > module T1 where > > data Foo = Foo Int String > data Bar = Bar Int Foo > > instance Ord Bar where > compare (Bar i _) (Bar j _) = compare i j > > instance Eq Bar where > (Bar i _) == (Bar j _) = i == j --T2.hs-- > module Main where > > import T1 > > data Zot = Zot !Bar !String deriving (Ord,Eq) > > main = putStrLn "Success" -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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deprecated non-standard syntax
by Andre W B Furtado 06 Apr '03

06 Apr '03

The following line: foreign import shutdownHaskellAndExit :: Int -> IO () causes a compiler warning: foreign declaration uses deprecated non-standard syntax Which is the correct way to use a foreign declaration? Thanks, -- Andre

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Waiting to hear from you.
by Dr.Williams Okun. 06 Apr '03

06 Apr '03

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ghc errrorformat for vim
by Martin Norbäck 04 Apr '03

04 Apr '03

Errors from the GHC haskell compiler looks something like this: Apa.hs:3: parse error (possibly incorrect indentation) Bepa.hs:15: Warning: Module `Cepa' is imported, but nothing from it is used \t (except perhaps to re-export instances visible in `Cepa') So I'd thought I'd make a vim 'errorformat' for it, and here it is: set errorformat+=%A%f:%l:\ %m,%A%f:%l:,%C%\\s%m,%Z I'm posting this to the mailing list to get comments, and to get indexed by the search engine, but without having to put this on a page.

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FFI and Concurrency
by Ahn Ki-yung 04 Apr '03

04 Apr '03

C call blocks the whole process, and Concurret module become meaningless. Isn't there any library or wrapper that can avoid ccall from blocking entire process ? -- Ahn Ki-yung

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RE: Modifying the simplifier
by Simon Peyton-Jones 04 Apr '03

04 Apr '03

Hmm. Some transformations are controlled by individual flags, but not all. I'm afraid there's no substitute here for checking out the code and looking at it. If you get stuck I'll try to help S | -----Original Message----- | From: glasgow-haskell-users-admin(a)haskell.org [mailto:glasgow-haskell-users- | admin(a)haskell.org] On Behalf Of David Sabel | Sent: 02 April 2003 13:32 | To: glasgow-haskell-users(a)haskell.org | | Is there an easy way to turn off some of the local transformations in | the simplifier? | | The background: | I'm writing my master thesis about compiling the unsafePerformIO in a "safe" | way | in the ghc. For that I used a nondeterministic semantics which simulates the | IO. | After a lot of theoretical work it has pointed out, that some of the local | transformations | of the ghc are no longer correct (from my point of view). Now I want to | implement a prototype by | modifying the ghc. Especially the eta-expansion, case-elimination must be | turned off, | inling in general is'nt correct too, so I would like to turn it off for now | and | later modify the implementation for this transformation. | | David Sabel | ----------- | JWGU Frankfurt | | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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How is non-blocking IO working ?
by Ahn Ki-yung 03 Apr '03

03 Apr '03

Document says GHC uses non-blocking IO to be thread friendly. But if it continues to poll on the non blocking file descriptor. It should cost much CPU load, but actually it doesn't : for example if a server is wating an input from a connected client, say using hGetLine, until input comes in from the network it should continue to poll until it succeeds to get some messages. But this does not seem to happen, if I look at the prcessor activity using 'top'. It does not consume CPU same as a blocked processed by blocked IO. How is non-blocking and thread working ? I can't understand.

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