- Haskell-Cafe - Haskell.org

The functional-object style seems to be gaining momentum.
by caseyh＠istar.ca 18 Jun '10

18 Jun '10

The functional-object style seems to be gaining momentum. Is there any way to convert monads into objects, so that beginners have an easier time with the syntax and thus we can attract more people to the language? :)

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Has anybody tried to upgrade Cabal on HP (Win 7)
by Daniel Kahlenberg 18 Jun '10

18 Jun '10

Hello, I recently installed HP 2010.1.0.0 within Windows 7 and wanted to upgrade the Cabal package to 1.8.0.6 today, sadly I got stuck on a failure building the "directory" package. So I tried to isolate the messages a bit and gave the following a try in a ghci session (1st time only with path to cygwin binaries/2nd time only with path to msys binaries added on my path variable, for both times I append the logging output): Prelude System.Cmd> > rawSystem "cabal" ["upgrade", "--constraint=base==4.*", "directory", > "-v3", "--user", > "--build-log=d:/temp/log/build-$$pkgid-$$compiler.log"] Maybe we can find the cause?! Greetz Daniel

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Re: [Haskell-cafe] What is Haskell unsuitable for?
by caseyh＠istar.ca 18 Jun '10

18 Jun '10

> If you want to use cool languages, you may have to get a cool job. I > know: it's easy to say and harder to accomplish. Most functional languages (e.g. Lisp, Haskell, ...) have a challenging time in industry since they require some savvy with multiple levels of higher abstractions and some savvy with mathematical ideas and some savvy with functional algorithms and data structures. Also, your manager has probably come up through the technical ranks on his/her OOA/OOD/OOP skills and sees you as a young (or not) upstart trying to show off. :)

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Fun Facts: A lazy bill
by Leonel Fonseca 18 Jun '10

18 Jun '10

I share this just for the sake of fun. In Costa Rica (Central America) a new series of bills are to be emitted and to celebrate bio-diversity some animal drawings are going to be used. Look at the new 10.000 colones bill: http://www.bccr.fi.cr/WebPages/PaginaInicio/NuevaFamilia/10.html Choose "reverso" in order to see the other side. -- Leonel Fonseca.

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Troubles Building LLVM
by Keith Sheppard 18 Jun '10

18 Jun '10

Hello All, I'm trying to get up and running with the very interesting llvm package[1] but I'm running into problems during the linking stage. keith@sugarglider-2:~/projects/third-party/llvm-hs-bindings/examples/> make clean all rm -f HelloJIT Fibonacci BrainF Vector Array DotProd Arith Align Struct Varargs *.o *.hi *.s *.bc Fib *.exe *.exe.manifest *~ ghc -Wall -optl -w --make -o HelloJIT.exe -main-is HelloJIT.main HelloJIT.hs [1 of 1] Compiling HelloJIT ( HelloJIT.hs, HelloJIT.o ) Linking HelloJIT.exe ... Undefined symbols: "_LLVMAddCondPropagationPass", referenced from: _ssCM_info in libHSllvm-0.7.1.1.a(Scalar.o) ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [HelloJIT.exe] Error 1 It's probably something very simple that I'm doing wrong since this is my first Haskell build linking against foreign libs. Do you know what I might be doing wrong? Here are the versions: Mac OS X 10.5.8 GHC 6.10.1 (waiting out a leopard installer bug [2]) llvm-2.7 installed to default location llvm package version 0.7.1.1 Thanks! BTW, the combination of this package plus the awesome Haskell parsers seem to make for a great compiler construction kit. I'm looking forward to playing around w/ llvm [1] http://hackage.haskell.org/package/llvm [2] http://trac.haskell.org/haskell-platform/ticket/110 -- keithsheppard.name

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Using Hint with a socket server
by Tom Jordan 18 Jun '10

18 Jun '10

I'm trying to receive small segments of Haskell code over a socket, and be able to evaluate them in real time in GHCI. I've already downloaded Hint and have run the test code, and it's working great. I'm also using the socket server code from Ch.27 of "Real World Haskell" and that is working well also. directly below is the function from the socket server code that handles the incoming messages. Instead of doing this: "putStrLn msg"... I want to send whatever is captured in "msg" to the GHC interpreter that is used in the Hint code, something like this: "eval msg". I'm not sure how to combine both of these functionalities to get them to work with each other.. -- A simple handler that prints incoming packets plainHandler :: HandlerFunc plainHandler addr msg = putStrLn msg Below is the full code for the socket server, then below that is "SomeModule" used in the Hint example test below that. -- file: ch27/syslogserver.hs import Data.Bits import Network.Socket import Network.BSD import Data.List type HandlerFunc = SockAddr -> String -> IO () serveLog :: String -- ^ Port number or name; 514 is default -> HandlerFunc -- ^ Function to handle incoming messages -> IO () serveLog port handlerfunc = withSocketsDo $ do -- Look up the port. Either raises an exception or returns -- a nonempty list. addrinfos <- getAddrInfo (Just (defaultHints {addrFlags = [AI_PASSIVE]})) Nothing (Just port) let serveraddr = head addrinfos -- Create a socket sock <- socket (addrFamily serveraddr) Datagram defaultProtocol -- Bind it to the address we're listening to bindSocket sock (addrAddress serveraddr) -- Loop forever processing incoming data. Ctrl-C to abort. procMessages sock where procMessages sock = do -- Receive one UDP packet, maximum length 1024 bytes, -- and save its content into msg and its source -- IP and port into addr (msg, _, addr) <- recvFrom sock 1024 -- Handle it handlerfunc addr msg -- And process more messages procMessages sock -- A simple handler that prints incoming packets plainHandler :: HandlerFunc plainHandler addr msg = putStrLn msg -- main = serveLog "8008" plainHandler ---------------------------------------------------------------------------------------------------------------- module SomeModule(g, h) where f = head g = f [f] h = f ---------------------------------------------------------------------------------------------------------------- import Control.Monad import Language.Haskell.Interpreter main :: IO () main = do r <- runInterpreter testHint case r of Left err -> printInterpreterError err Right () -> putStrLn "that's all folks" -- observe that Interpreter () is an alias for InterpreterT IO () testHint :: Interpreter () testHint = do say "Load SomeModule.hs" loadModules ["SomeModule.hs"] -- say "Put the Prelude, Data.Map and *SomeModule in scope" say "Data.Map is qualified as M!" setTopLevelModules ["SomeModule"] setImportsQ [("Prelude", Nothing), ("Data.Map", Just "M")] -- say "Now we can query the type of an expression" let expr1 = "M.singleton (f, g, h, 42)" say $ "e.g. typeOf " ++ expr1 say =<< typeOf expr1 -- say $ "Observe that f, g and h are defined in SomeModule.hs, " ++ "but f is not exported. Let's check it..." exports <- getModuleExports "SomeModule" say (show exports) -- say "We can also evaluate an expression; the result will be a string" let expr2 = "length $ concat [[f,g],[h]]" say $ concat ["e.g. eval ", show expr1] a <- eval expr2 say (show a) -- say "Or we can interpret it as a proper, say, int value!" a_int <- interpret expr2 (as :: Int) say (show a_int) -- say "This works for any monomorphic type, even for function types" let expr3 = "\\(Just x) -> succ x" say $ "e.g. we interpret " ++ expr3 ++ " with type Maybe Int -> Int and apply it on Just 7" fun <- interpret expr3 (as :: Maybe Int -> Int) say . show $ fun (Just 7) -- say "And sometimes we can even use the type system to infer the expected type (eg Maybe Bool -> Bool)!" bool_val <- (interpret expr3 infer `ap` (return $ Just False)) say (show $ not bool_val) -- say "Here we evaluate an expression of type string, that when evaluated (again) leads to a string" res <- interpret "head $ map show [\"Worked!\", \"Didn't work\"]" infer >>= flip interpret infer say res say :: String -> Interpreter () say = liftIO . putStrLn printInterpreterError :: InterpreterError -> IO () printInterpreterError e = putStrLn $ "Ups... " ++ (show e)

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coming soon: ICFP programming contest 2010
by J.Waldmann 17 Jun '10

17 Jun '10

http://icfpcontest.org/2010/ will start roughly 12 hours from now. 221022000022010112201010022001122011110220010

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Understanding GHC allocations
by Roman Cheplyaka 17 Jun '10

17 Jun '10

I'm trying to optimize the following program: http://github.com/feuerbach/particles/blob/303c8a17c9b732e22457b5409bdce4b7… Of course general suggestions are welcome (BTW I'm going to give a try to vector), but currently I'm concerned with two questions: 1. Heavy allocations in 'distance' function. Here is (part of) the profile: COST CENTRE MODULE %time %alloc ticks bytes d2 Main 9.0 22.0 290 600000000 d Main 8.6 65.9 278 1800000000 d1 Main 7.5 11.0 242 299700000 >From reading core I got the impression that everything is strict & unboxed. Perhaps this is related to creating some closures? How to get rid of those allocations? 2. Again from reading the core I learned that although 'l' and other constants are inlined, their type is boxed Double. This makes sense since CAFs are evaluated on demand, but obviously in this particular case it does not make sense, so can I somehow make them unboxed? -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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What is Haskell unsuitable for? Dis-functional programming!
by caseyh＠istar.ca 17 Jun '10

17 Jun '10

:)

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Re: [Haskell-beginners] Re: Accounting Engine in Haskell
by Patrick LeBoutillier 17 Jun '10

17 Jun '10

Hi, > Keep in mind that you have to invest some time in learning Haskell > before you can reap the benefits. For an example of the latter, see also > > Paul Hudak, Mark P. Jones. > Haskell vs. Ada vs. C++ vs. Awk vs. ..., > An Experiment in Software Prototyping Productivity > http://haskell.org/papers/NSWC/jfp.ps This paper was very interesting to me. Does anyone know if the full source code for the Haskell prototype is available somewhere? Patrick -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

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