- Haskell-Cafe - Haskell.org

alphanum in infix constructors (and possibly functions as well) - why not?
by Ozgur Akgun 04 Jun '10

04 Jun '10

Hi all, The constructor names in Haskell need to obey one of the two following rules: - either starts with a capital letter and contains alphanumeric characters afterwards, (including _ I guess) - or starts with a colon (:) and only contains symbols afterwards The first one is used Prefix by default, and the second ose is used infix by default. What stops us from allowing alphanum characters appear in the Infix version (after the colon)? Can't it be relaxed to only start woth a colon? So I want to be able to say something like: data Expr = Expr :< Expr -- checks for LT betwen two Expr's | Expr :<2 Expr -- a different implementation of the same thing maybe | Expr :<veryfast Expr -- and the veryfast implementation of it (just a silly example I could think of now.) Best, Ozgur Akgun

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Strange GHC messages?
by Liam O'Connor 04 Jun '10

04 Jun '10

Hi all, I've got some strange GHC output that doesn't seem to be affecting my program adversely but I thought I should post about it cos it's disquieting mkUsageInfo: internal name? r{tv aIR} mkUsageInfo: internal name? s{tv aIS} It seems to be complaining about this newtype declaration: > newtype ThreadStateM r s v = ThreadState { unbox :: StateT s (ReaderT r IO) v } > deriving (Monad, Functor, MonadIO, MonadState s, MonadReader r) (uses newtype deriving) I'm not sure what the problem here is? Cheers. ~Liam

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Re: [Haskell-cafe] Weird socket problem on Mac OS X
by Antoine Latter 04 Jun '10

04 Jun '10

On Fri, Jun 4, 2010 at 12:11 AM, Arnaud Bailly <arnaud.oqube(a)gmail.com> wrote: > Yes, I have also seen the other post on the same topic, but it seemed > to refer to the PortNumber in Network.Socket with a PortNum > constructor I think, not the one in Network (but I am probably > misleading myself as one is a reexportation of the other...). > But then I got. > > Slim\SlimClientIO.hs:26:51: > No instance for (Num PortID) > arising from a use of `fromInteger' > at Slim\SlimClientIO.hs:26:51-61 > Possible fix: add an instance declaration for (Num PortID) > In the first argument of `($)', namely `fromInteger' > In the expression: fromInteger $ slimport $ slimConfig st > In the definition of `port': > port = fromInteger $ slimport $ slimConfig st > Oops! I didn't read carefully enough. That's what I get for trying to program without haddocks or GHCi in front of me. I am glad you have something that works. Antoine

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Fwd: [Haskell-cafe] Weird socket problem on Mac OS X
by Arnaud Bailly 04 Jun '10

04 Jun '10

---------- Forwarded message ---------- From: Arnaud Bailly <arnaud.oqube(a)gmail.com> Date: Fri, Jun 4, 2010 at 11:59 AM Subject: Re: [Haskell-cafe] Weird socket problem on Mac OS X To: Antoine Latter <aslatter(a)gmail.com> Hello, I managed to solve the problem using Network.Socket instead of Network. Is this a bug or a feature ? Arnaud On Fri, Jun 4, 2010 at 7:11 AM, Arnaud Bailly <arnaud.oqube(a)gmail.com> wrote: > Yes, I have also seen the other post on the same topic, but it seemed > to refer to the PortNumber in Network.Socket with a PortNum > constructor I think, not the one in Network (but I am probably > misleading myself as one is a reexportation of the other...). > But then I got. > > Slim\SlimClientIO.hs:26:51: > No instance for (Num PortID) > arising from a use of `fromInteger' > at Slim\SlimClientIO.hs:26:51-61 > Possible fix: add an instance declaration for (Num PortID) > In the first argument of `($)', namely `fromInteger' > In the expression: fromInteger $ slimport $ slimConfig st > In the definition of `port': > port = fromInteger $ slimport $ slimConfig st > > :-( > Thanks > > Arnaud > > On Fri, Jun 4, 2010 at 1:46 AM, Antoine Latter <aslatter(a)gmail.com> wrote: >> Hi Arnaud, >> >> One thing you might want to try is to stop using the PortNumber data >> constructor, and instead rely on 'fromInteger' to do the right thing. >> >> The data constructor assumes that it's argument is in network byte order, >> which won't always be the case. >> >> It's not obvious that the constructor should be avoided - this is the second >> time today I've seen this! >> >> Take care, >> Antoine >> >> On Jun 3, 2010 5:13 PM, "Arnaud Bailly" <arnaud.oqube(a)gmail.com> wrote: >> >> Hello, >> I have the following code which works ok on Linux and Windows XP, but >> fails on Mac OS X with error message: >> >> Connect: does not exist (connection refused) >> >> The server: >> >> doStartstate = do pr <- liftIO $ runProcess ... >> liftIO $ threadDelay 500000 >> st <- get >> put st { slimHandle = Just pr } >> >> >> The client: >> >> fetchAnswers st msgs = liftIO $! do let port = PortNumber $ >> fromInteger $ port $ config st >> cnx <- connectTo "localhost" port >> >> Help most welcome, thanks >> >> Arnaud >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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Haskell opportunity at investment bank
by Pearse, Chris 04 Jun '10

04 Jun '10

Hello, I'm looking for a developer with expertise in Haskell for an investment bank in London. The role will involve working on a multi-asset, multi-region, pricing, risk and trade lifecycle solution for the wholesale banking division. Solutions are developed using Java, C#/WPF, C++ and make heavy use of Haskell. The requirement is for an experienced developer with in-depth knowledge of functional programming in Haskell - ideally in a commercial environment. If interested, please feel free to send your CV through or call me to discuss. Thanks, Chris Pearse 0207 469 5050 http://www.linkedin.com/pub/3/9a1/142 ------------------------------------------------------------------------------- Huxley Associates - Professional Recruitment Solutions Established in 1995, Huxley Associates is an international recruitment consultancy. We provide bespoke recruitment services to the Accountancy & Finance, Banking Technology, Energy, Engineering, Global Markets, Human Resources, IT, Oil & Gas, Sales & Marketing, and Supply Chain sectors. With over 400 specialist recruitment professionals, we are consistently able to meet the high recruitment needs of a diverse range of companies across the UK, Europe, Asia and the United States. This email message may contain confidential and/or privileged information, and is intended solely for the addressee(s). If you have received this email in error, please notify Huxley Associates immediately. Unauthorised copying, disclosure or distribution of the material in this email is forbidden. If you do not want to receive emails from us about our services in future, or if you want to query or qualify how your personal data is held by us (for details on this see our privacy statement http://www.huxley.co.uk/privacy_policy.html ) please e-mail audit.data(a)huxley.com.

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Efficient string construction
by Kevin Jardine 04 Jun '10

04 Jun '10

(I've done a basic Google search on this with no results. Apologies if this has been asked before.) I am coding a web application in which the content is a Unicode string built up over multiple functions and maintained in a State structure. I gather that the String module is inefficient and that Data.Text would be a better choice. Is it more efficient to build up a list of Text objects over time and combine them together with a single Data.Text.concat for the final output or to run Data.Text.append for each new string so that I am maintaining a single Text object rather than a list? As Data.Text.append requires copying both strings each time, my gut feeling is that concat would be much more efficient, but Haskell has surprised me before, so I wanted to check. Kevin

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ICFP Programming Contest
by Wouter Swierstra 04 Jun '10

04 Jun '10

This year's ICFP Programming Contest will begin on June 18th (12:00 Noon GMT) and will run till June 21st (12:00 Noon GMT). As in the previous editions, this is your chance to show that your favorite programming language is better than all others! The problem statement and further information will become available at: http://icfpcontest.org/2010/ Feel free to contact ifcpcont at imn dot htwk-leipzig dot de for further questions. Good luck! Wouter

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Simplest reference for how to build GHC head + get it running w/ cabal/haskell-platform?
by Ryan Newton 04 Jun '10

04 Jun '10

What's the easiest reference for how to build GHC head and get it up and running with cabal/haskell-platform? I simply installed 6.12 + haskell-platform then built ghc-6.13.xx and rebuilt only the packages I needed with "cabal install --reinstall". Perhaps this is not the recommended way. Indeed, something must be wrong because I can't build certain packages. (I have problems with "base" dependencies.) For example: $ cabal install QuickCheck Resolving dependencies... cabal: cannot configure QuickCheck-1.2.0.0. It requires base ==3.* For the dependency on base ==3.* there are these packages: base-3.0.3.1 and base-3.0.3.2. However none of them are available. base-3.0.3.1 was excluded because of the top level dependency base -any base-3.0.3.2 was excluded because of the top level dependency base -any Thanks! -Ryan

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Re: [Haskell-cafe] Weird socket problem on Mac OS X
by Antoine Latter 03 Jun '10

03 Jun '10

Hi Arnaud, One thing you might want to try is to stop using the PortNumber data constructor, and instead rely on 'fromInteger' to do the right thing. The data constructor assumes that it's argument is in network byte order, which won't always be the case. It's not obvious that the constructor should be avoided - this is the second time today I've seen this! Take care, Antoine On Jun 3, 2010 5:13 PM, "Arnaud Bailly" <arnaud.oqube(a)gmail.com> wrote: Hello, I have the following code which works ok on Linux and Windows XP, but fails on Mac OS X with error message: Connect: does not exist (connection refused) The server: doStartstate = do pr <- liftIO $ runProcess ... liftIO $ threadDelay 500000 st <- get put st { slimHandle = Just pr } The client: fetchAnswers st msgs = liftIO $! do let port = PortNumber $ fromInteger $ port $ config st cnx <- connectTo "localhost" port Help most welcome, thanks Arnaud _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Language Shootout reverse-complement benchmark
by Louis Wasserman 03 Jun '10

03 Jun '10

Hey, I was looking at the reverse-complement benchmark on the Language Shootout, and among other things, I noticed that the Haskell implementation was using (filter (/= '\n')) on ByteStrings, and also using lists as queues. I had a few improvements which using -fasm seem to yield about a 19% improvement in speed, and a 35% reduction in allocation, on my computer. (If both programs are compiled with -fllvm -- I'm not sure whether or not that's fair game on the Shootout -- my implementation is 35% faster, and does 10% less allocation.) I've checked my code on the Shootout's test input, as well. Mostly, the improvement comes from a tightly specialized version of (filter (/= '\n')), although eliminating an intermediate list entirely (and one used in a queuelike fashion) didn't seem to hurt. I managed to cut the program to a point where the program size is about the same as before. The code is at http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25865; the previous implementation is at http://shootout.alioth.debian.org/u32/program.php?test=revcomp&lang=ghc&id=2 . Let the arguing begin? Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

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