June 2013 - Beginners

Diamantina - Lista aprovados
by David Anderson 05 Jun '13

05 Jun '13

Diamantina ALINE ALVES DE SOUZA, KETLLY CAPISTRANO DO NASCIMENTO, FELIPE DE ALMEIDA BARBOSA, NATALIA CARNICELLI CARVALHO OLIVEIRA, JOÃO CARLOS MOREIRA DE CARVALHO, CÍNTIA FRANCISCA DE OLIVEIRA, MARCOS PAULO DE ARAUJO RIBEIRO, ISABEL CRISTINA DE SOUZA DE LIMA. ROZÂNGELA PINHEIRO LEITE, ELAINE FERREIRA LEITE, MARTONIO RODRIGUES ANGELIM FONTENELE, JOSÉ ORLANDO DA SILVA OLIVEIRA, VANUSA KEZIA SANTOS MESQUITA. Barro Alto. Varzedo ANA PAULA PEREIRA DA SILVA, LUCAS ARAUJO DA SILVA, GABRIEL LIMA VALENTIM, QUEZIA GOMES SNTOS, JOÃO CARLOS MOREIRA DE CARVALHO, DAYA VALE DOS SANTOS, MARIA JOSEANE DE SOUZA, JOAO HUDSON OLIVEIRA NUNES. SUÉNIA CONCEIÇÃO SILVA, BRUNO MORAES NASCIMENTO, LUIZ GUSTAVO SILVA CRISPIM DE LIMA, HYAGO KENNEDY FERNANDES DE SOUSA, RICHELLE DANTAS SILVA. Aripuanã. Almenara ALINE ALVES DE SOUZA, KETLLY CAPISTRANO DO NASCIMENTO, FELIPE DE ALMEIDA BARBOSA, NATALIA CARNICELLI CARVALHO OLIVEIRA, JOÃO CARLOS MOREIRA DE CARVALHO, CÍNTIA FRANCISCA DE OLIVEIRA, MARCOS PAULO DE ARAUJO RIBEIRO, ISABEL CRISTINA DE SOUZA DE LIMA. ROZÂNGELA PINHEIRO LEITE, ELAINE FERREIRA LEITE, MARTONIO RODRIGUES ANGELIM FONTENELE, JOSÉ ORLANDO DA SILVA OLIVEIRA, VANUSA KEZIA SANTOS MESQUITA. Aripuanã.

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Haskell's Scrap Your Boilerplate (SYB) - applying transformation only once instead of everywhere
by Duc le anh 04 Jun '13

04 Jun '13

What's the best way to apply a transformation to a tree only once instead of everywhere using SYB? For instance, in the following simplified expression, there are several instances of Var "x", and I want to replace the first instance with Var "y" only. data Exp = Var String | Val Int | Plus Exp Exp |... myExp = Val 5 `Plus` Var "x" `Plus` Val 5 `Plus` Var "x" ... This can't be done using the everywhere combinator since it will try to transform all instances of Var "x" toVar "y". -- Duc A. Le PS: I also asked this on stackoverflow but figured that I might get a faster response here. Thank you!

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Re: [Haskell-beginners] FFI, export a ByteString
by Antoine Latter 02 Jun '13

02 Jun '13

The function 'castStablePtrToPtr' does not actually return a pointer you can usefully de-reference in C - it just gives you a value that will fit into a 'void*' in C-land. A StablePtr is, conceptually, just a pointer-sized index into an array maintained by the Haskell runtime, you can only de-reference it in Haskell. But you can pass it around in C because it fits into a pointer-sized variable or struct member. On Thu, Apr 11, 2013 at 10:59 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: > My function in Haskell takes a CString and returns a ByteString (of Word8). > > I tried to put this function in a Haskell made Windows dll. I want to use > this function in a program written in C. > > > > The most simple program that compiled was: > > > > Import qualified B.ByteString as B > > import Foreign.StablePtr > > import Foreign.C.String > > import Foreign.Ptr > > > > foreign export stdcall parseRuitType :: CString -> IO (Ptr ()) > > parseRuitType s = do > > p <- (newStablePtr ( B.pack [10,11,12])) > > return $ castStablePtrToPtr p > > > > For testing I ignore s. > > > > In the C-program : > > hs_init(NULL,NULL) > > res = parseRuitType (“5” ) > > No errors, but the returned value res (or the dereferenced res) makes no > sense (not 10,11,12). > > > > My idea was: the result of the function(a ByteString of Word8) must be > locked. No garbage collection. But newStablePtr does not return a pointer. > So I have to convert the newStablePtr to a real pointer and then coerce this > in the C program to a pointer to a array of word8…? > > I’ve tried to return the ByteString in the Haskell function. But now the > compiler complains: Unacceptable result type in foreign declaration : > B.ByteString > > > > I’am missing the big picture. Any ideas? > > > > Greetings > > Kees > > > > > > > > > > > > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners >

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data-files for test-suite
by harry 02 Jun '13

02 Jun '13

My cabal file has a test-suite section which requires an input file. I can get it with data-files and getDataFileName, but presumably this will be installed with the package. However, I only need it for running the exitcode-stdio-1.0. Is there another way of accessing test data?

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Re: [Haskell-beginners] Q 2 of 2: GUI and turnkey compiler?
by Gan Uesli Starling 01 Jun '13

01 Jun '13

I think I need to define what is meant by turn-key compiler. That is what they called it in JForth. In Perl this same feature goes by the term "packed archive" and in LabVIEW they call it a "built application". It is a feature in those languages whereby you can issue an standalone *.exe having within itself, complete unto itself, all that is needed to run the script, program, application. The output appears as a single file to the end user with the expected extension of *.exe but functions in fact more like those ZIP installers which also come with *.exe extensions. The size will be bloated, since packed archive has within it all from the parent language, modules included, that are needful to run the script, at least for Perl. For JForth it was much the same. For LabVIEW the output of a "build" requires to have the "runtime engine" installed, but which, once installed, is good for ALL applictions and will run them but not allow editing. So, it would be something to allow an author to issue programs which end-users would NOT have to know anything about Haskell itself and would have to, at most, perform a two-step, wholly automatic installation procedure. Short of this, anything I might aspire to give away free to the public en masse, could not conceivably be written in Haskell. In which case, I'll respectfully bow out from endeavoring to learn it myself, however useful it serves for many another purpose.

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Abstracting Data.List
by Giacomo Tesio 01 Jun '13

01 Jun '13

I'm looking for a class abstracting Data.List. I mean something that enable the use of say head, map, take and so on into different kind of types. Is there already something like that? Giacomo

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help with IO and guards
by Miro Karpis 31 May '13

31 May '13

Please, I'm trying to do some user user input validation, but it looks like my approach is not correct. Here is my code: textInput :: IO () textInput | dataIn == "bye" = return () | otherwise = textInput where dataIn <- getLine the idea is that when user inputs "bye" the program should end/return. Problem is that I'm getting 'parse error on input `<-'' error. How can I achieve it? Another question I have is: how can I have more actions in guard, when the condition is valid. Something like (write on IO + return if dataIn == "bye): textInput :: IO () textInput *| dataIn == "bye" = (puStrLn "quitting", return () ) -- * | otherwise = textInput where dataIn <- getLine Millions of thanks for any kind of input.. Cheers, Miro

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