August 2001 - Glasgow-haskell-users

Simple implicit parameters question
by brk＠jenkon.com 27 Aug '01

27 Aug '01

Hi all, Using one implicit parameter works fine for me, but when I use two, things seem to go astray. Here's a highly contrived example: main = do putStrLn $ mytrim with ?width = 20 with ?line = "The quick brown fox jumped over the lazy dog" mytrim | ?width > length ?line = ?line | otherwise = take ?width ?line But ghc complains: $ ghc -o scratch.exe scratch.hs -fglasgow-exts scratch.hs:8: Unbound implicit parameter `?width :: Int' arising from use of implicit parameter `?width' at scratch.hs:8 In the first argument of `(>)', namely `?width' In the definition of `mytrim': ?width > (length ?line) scratch.hs:8: Unbound implicit parameter `?line :: [Char]' arising from use of implicit parameter `?line' at scratch.hs:8 In the first argument of `length', namely `?line' In the second argument of `(>)', namely `length ?line' Can someone please tell me what I'm doing wrong? Thanks, Bryn Keller Senior Software Engineer Jenkon brk(a)jenkon.com

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tail -f behaviour in ghc.
by Alex Ferguson 27 Aug '01

27 Aug '01

I suspect this is more of a "my patchy knowledge about file handles" question than a ghc or a Haskell question, but at the risk of revealing same in public... Is it possible to implement "follow mode" behaviour, a la tail -f, without using "seek" (or hSetPosn, which I assume is essentially seek slightly abstractified). Essentially this comes down to whether once a handle reaches "eof", whether than can be subsequently falsified. I suspect the intended and actual behaviour in all cases is "as per Unix handles", but shouldn't it in principle be specified independently thereof? Cheers, Alex.

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RE: SocketPrim.socketToHandle
by Simon Marlow 27 Aug '01

27 Aug '01

> Currently this functions has the type > > > SocketPrim.Socket -> PrelHandle.IOMode -> IO PrelIOBase.Handle > > Could you change the order of the arguments, please? I can`t see > any particular requirement of the socket being the first argument, > but swapping it with IOMode would eliminate an additional 'flip' > when mapping socketToHandle over a list of sockets, e.g.: > > > handles <- mapM (socketToHandle ReadMode) sockets Yes, but currently it matches the argument order of openFile. On the grounds that the change is unforced and would break existing programs, I'm not enclined to change it. However, if there's a concensus then this kind of change can happen when we switch over to the new libraries - libraries(a)haskell.org is the right place to discuss this. Cheers, Simon

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SocketPrim.socketToHandle
by Volker Stolz 25 Aug '01

25 Aug '01

Currently this functions has the type > SocketPrim.Socket -> PrelHandle.IOMode -> IO PrelIOBase.Handle Could you change the order of the arguments, please? I can`t see any particular requirement of the socket being the first argument, but swapping it with IOMode would eliminate an additional 'flip' when mapping socketToHandle over a list of sockets, e.g.: > handles <- mapM (socketToHandle ReadMode) sockets -- Volker Stolz * vs(a)foldr.org * PGP + S/MIME

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Newbie ST/Monad Question
by Carl McTague 24 Aug '01

24 Aug '01

That's so bizarre! It works now and I can't reproduce that strange output at all (and the Union-find code works flawlessly now, too)! I'm sure I'm more baffled than you. I feel like a real idiot. Sorry about that. But thanks! You've exorcized the unnatural daemon from my computer! Carl

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Re: Newbie ST/Monad Question
by Marcin 'Qrczak' Kowalczyk 24 Aug '01

24 Aug '01

Fri, 24 Aug 2001 11:28:56 -0600, Carl McTague <mctague(a)one.net> pisze: > import ST > > three :: Int > three = runST (do v<-newSTRef 0 > writeSTRef v 3 > readSTRef v) > > main = print (three*3) > > when this is compiled and run using ghc, it prints > > carl@exp(monad) ./a.out > <<ST action>> Are you sure? It prints 9 for me. > what need I do to make it print 6? Change one of 3's to 2 :-) -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Newbie ST/Monad Question
by Carl McTague 24 Aug '01

24 Aug '01

Dear Haskell Hackers, Please forgive me if I've sent this is the wrong mailing list. I'm writing a simple union/find implementation using the ST library, but I've run into some kind of conceptual problem that I've been able to isolate in the following: import ST three :: Int three = runST (do v<-newSTRef 0 writeSTRef v 3 readSTRef v) main = print (three*3) when this is compiled and run using ghc, it prints carl@exp(monad) ./a.out <<ST action>> carl@exp(monad) what need I do to make it print 6? Sincerely, Carl

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Re: Haskell on Alpha
by Ken Shan 24 Aug '01

24 Aug '01

Hello, I've finally made a release of my port of GHC 5.00.2 to alpha-dec-osf3. It is at: http://www.eecs.harvard.edu/~ccshan/ghc/ This is my first time building a binary distribution (not to mention my first time participating in GHC development)... Please let me know if you find any problems. Thanks! -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig I saw my inner child once, on a milk carton.

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MPI status?
by Duncan Coutts 24 Aug '01

24 Aug '01

Hi all, I'm doing an internship at Cray Inc this summer and I might get the opportunity of some computer time on a T3E machine. Now I am also a great Haskell fan and have been wondering about the possibility of getting parallel Haskell running on a real super-computer. I've read that someone is working on porting ghc's parallel features to an MPI implementation and also that someone recently got the alpha port working again. In case you don't know a T3E is a distributed memory alpha based super-computer. It supports MPI & pthreads. So my question is, what is the state of the art? What is the state of the MPI port? Does the alpha port work sufficiently well. One potential problem I can see is that I'm not sure gcc is avaliable on the T3E and I'm not sure how dependant ghc is upon the various GNU C extensions. So, if I can get an account, I'll have untill the end of September to test anything anyone can give me. You know they still program these machines in C, C++ & Fortran. Shocking! ;-) Duncan

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Newbie: Mutable Arrays
by Saswat Anand 24 Aug '01

24 Aug '01

Hi, I find two versions of Mutable arrays ie STArray and IOArray. What is the difference between them. Where each of them are supposed to be used? Thanks, Saswat

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