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The Monad.Reader (11) - Call for Copy
by Wouter Swierstra 09 May '08

09 May '08

Call for Copy The Monad.Reader - Issue 11 Please consider writing something for the next issue of The Monad.Reader. The deadline for Issue 11 is ** August 1, 2008 ** It doesn't matter if you're a respected researcher or if you have only just started learning Haskell, get your thoughts together and write an article for The Monad.Reader! The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but more enduring than a wiki-page or blog. There have been a wide variety of articles, including: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. * Submission Details * Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (wss at cs.nott.ac.uk). Articles should be written according to the guidelines available from http://www.haskell.org/haskellwiki/The_Monad.Reader Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll sort something out. All the best, Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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FFI: Creating a Storable for a C-struct composed of char arrays
by Olivier Boudry 09 May '08

09 May '08

Hi all, I'm trying to make RFC calls to SAP using the nwsaprfc library. Some structs defined in the library contains arrays (byte or word arrays). For example: typedef struct _RFC_ATTRIBUTES { SAP_UC dest[64+1]; /* RFC destination */ SAP_UC host[100+1]; /* Own host name */ SAP_UC partnerHost[100+1]; /* Partner host name */ SAP_UC sysNumber[2+1]; /* R/3 system number */ SAP_UC sysId[8+1]; /* R/3 system name */ SAP_UC client[3+1]; /* Client */ SAP_UC user[12+1]; /* User */ SAP_UC language[2+1]; /* Language */ ... continued }}RFC_ATTRIBUTES, *P_RFC_ATTRIBUTES; I would like to create a Haskell Storable counterpart of this structure. Using http://therning.org/magnus/archives/tag/hsc2hs as an starting point, I could create Storable for structures containing fields with basic types. Before working on the real data structures I wrote a more simple example to play with: -- File: ArrayStruct.h -- typedef struct _ArrayStruct { char a[10+1]; char b[20+1]; char c[30+1]; } ArrayStruct, *P_ArrayStruct; -- File: ArrayStruct.c -- #include "ArrayStruct.h" void print_array_struct(ArrayStruct *f) { printf("%s\n", __FUNCTION__); printf("f->a: %s\n", f->a); printf("f->b: %s\n", f->b); printf("f->c: %s\n", f->c); } -- File: HArrayStruct.hsc {-# OPTIONS -ffi #-} module Main where import Foreign import Foreign.C.Types #include "ArrayStruct.h" data HArrayStruct = HArrayStruct { a :: String, b :: String, c :: String } type HarrayStructPtr = Ptr HArrayStruct foreign import ccall "static ArrayStruct.h print_array_struct" f_print_array_struct :: ArrayStructPtr -> IO () instance Storable HArrayStruct where sizeOf _ = (#size ArrayStruct) alignment _ = alignment (undefined :: CInt) peek _ = error "peek is not implemented" poke ptr (HArrayStruct a' b' c') = do (#poke ArrayStruct, a) ptr a' (#poke ArrayStruct, b) ptr b' (#poke ArrayStruct, c) ptr c' printArrayStruct as = with as f_print_array_struct main = printArrayStruct $ HArrayStruct { a="some", b="test", c="data" } -- End of files Of course it won't work as HArrayStruct in file HArrayStruct.hs uses Strings and String is not an instance of Storable. Ideally I would need some sort of Storable array of char. Is Data.Storable.Array the type I'm looking for? Could someone point me to some code using the same kind of structures? Thanks, Olivier.

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GHC API: how to get the typechecked AST?
by Gerbo Engels 09 May '08

09 May '08

Hello all, In the GHC Commentary [1] I can read that the type checker adds type information to the syntax tree. So I would expect that there is a way to get a syntax tree of type HsModule Id. The GHC API provides functions checkModule and checkAndLoadModule which both return a CheckedModule that contains the parsedSource :: Located (HsModule RdrName) and typecheckedSource :: LHsBinds Id. But it doesn't include anything of type HsModule Id. I don't see how to unify the parsedSource and typecheckedSource to get the syntax tree parametrised by Id instead of RdrName (and containing the type information), and the API doesn't seem to provide such functionality (or did I miss something?). Can anyone help? Or indicate where in the parsedSource the LHsBinds should be placed? Regards, Gerbo Engels [1] http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/HsSynType#Deco…

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"resource exhausted"
by Galchin, Vasili 09 May '08

09 May '08

Hello, I am running some monadic code that I have written. I double checked my code and it seems to be ok (no guarantee though). I am getting a "resource exhausted (Message too long)". I just did a google on "resource exhausted" and saw a few posts on the number of open files which is obviously not my case. Any ideas? Kind regards, Vasili

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REMINDER: Haskell Communities and Activities Report
by Janis Voigtlaender 09 May '08

09 May '08

Dear Haskellers, It is not yet too late to contribute to the 14th edition of the HC&A Report. The deadline is this weekend, Saturday, 10 May 2008. If you haven't already, please write an entry for your new project or update your old entry. Please mail your entries to <hcar at haskell dot org> in plain text or LaTeX format. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2008-April/020378.html We look forward to receiving your contributions. Thanks a lot, Andres and Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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A Cabal problem
by Mario Blazevic 08 May '08

08 May '08

I have a problem with Cabal: it doesn't seem to pick up the "Main-is:" option from the configuration file. Here's my "scc.cabal" file. Note the "Main-is:" line: > Name: scc > Version: 0.1 > Cabal-Version: >= 1.2 > Build-Type: Simple > License: GPL > License-file: LICENSE.txt > Copyright: (c) 2008 Mario Blazevic > Author: Mario Blazevic > Maintainer: blamario(a)yahoo.com > Synopsis: Streaming component combinators > > Executable shsh > Main-is: Shell.hs > Other-Modules: Foundation, ComponentTypes, Components, Combinators > Build-Depends: base, containers, process, readline, parsec > > Library > Exposed-Modules: Foundation, ComponentTypes, Components, Combinators > Build-Depends: base, containers And below are the outputs of Cabal configure and build commands. Note the absence of "--main-is" ghc command-line option. I'm doing this on Ubuntu 8.04 Linux, but I get the same problem with Gentoo. Is there something wrong with my configuration file, or is this a bug in Cabal? > ~/scc/pipe$ runhaskell Setup.lhs configure --verbose --prefix=~ > Configuring scc-0.1... > Dependency base-any: using base-3.0.1.0 > Dependency containers-any: using containers-0.1.0.1 > Dependency process-any: using process-1.0.0.0 > Dependency readline-any: using readline-1.0.1.0 > Dependency parsec-any: using parsec-2.1.0.0 > Using compiler: ghc-6.8.2 > Using install prefix: ~ > Binaries installed in: ~/bin > Libraries installed in: ~/lib/scc-0.1/ghc-6.8.2 > Private binaries installed in: ~/libexec > Data files installed in: ~/share/scc-0.1 > Documentation installed in: ~/share/doc/scc-0.1 > No alex found > Using ar found on system at: /usr/bin/ar > No c2hs found > No cpphs found > No ffihugs found > Using ghc version 6.8.2 found on system at: /usr/bin/ghc > Using ghc-pkg version 6.8.2 found on system at: /usr/bin/ghc-pkg > No greencard found > Using haddock version 0.8 found on system at: /usr/bin/haddock > No happy found > No hmake found > Using hsc2hs version 0.66-ghc found on system at: /usr/bin/hsc2hs > No hscolour found > No hugs found > No jhc found > Using ld found on system at: /usr/bin/ld > No nhc98 found > No pfesetup found > Using pkg-config version 0.22 found on system at: /usr/bin/pkg-config > Using ranlib found on system at: /usr/bin/ranlib > Using tar found on system at: /bin/tar > > ~/scc/pipe$ runhaskell Setup.lhs build --verbose > Creating dist/build (and its parents) > Creating dist/build/autogen (and its parents) > Preprocessing library scc-0.1... > Preprocessing executables for scc-0.1... > Building scc-0.1... > Building library... > Creating dist/build (and its parents) > Creating dist/build (and its parents) > /usr/bin/ghc -package-name scc-0.1 --make -hide-all-packages -i > -idist/build/autogen -idist/build -i. -Idist/build -odir dist/build > -hidir dist/build -stubdir dist/build -package base-3.0.1.0 -package > containers-0.1.0.1 -package process-1.0.0.0 -package readline-1.0.1.0 > -package parsec-2.1.0.0 -O Foundation ComponentTypes Components Combinators > [1 of 4] Compiling Foundation ( Foundation.hs, > dist/build/Foundation.o ) > [2 of 4] Compiling ComponentTypes ( ComponentTypes.hs, > dist/build/ComponentTypes.o ) > [3 of 4] Compiling Components ( Components.hs, > dist/build/Components.o ) > [4 of 4] Compiling Combinators ( Combinators.hs, > dist/build/Combinators.o ) > Linking... > /usr/bin/ar q dist/build/libHSscc-0.1.a dist/build/Foundation.o > dist/build/ComponentTypes.o dist/build/Components.o dist/build/Combinators.o > /usr/bin/ar: creating dist/build/libHSscc-0.1.a > /usr/bin/ld -x -r -o dist/build/HSscc-0.1.o.tmp dist/build/Foundation.o > dist/build/ComponentTypes.o dist/build/Components.o dist/build/Combinators.o > Building executable: shsh... > Creating dist/build/shsh (and its parents) > Creating dist/build/shsh/shsh-tmp (and its parents) > Creating dist/build/shsh/shsh-tmp (and its parents) > /usr/bin/ghc -o dist/build/shsh/shsh --make -hide-all-packages -i > -idist/build/autogen -idist/build/shsh/shsh-tmp -i. > -Idist/build/shsh/shsh-tmp -odir dist/build/shsh/shsh-tmp -hidir > dist/build/shsh/shsh-tmp -stubdir dist/build/shsh/shsh-tmp -package > base-3.0.1.0 -package containers-0.1.0.1 -package process-1.0.0.0 > -package readline-1.0.1.0 -package parsec-2.1.0.0 -O ./Shell.hs > [1 of 5] Compiling Foundation ( Foundation.hs, > dist/build/shsh/shsh-tmp/Foundation.o ) > [2 of 5] Compiling ComponentTypes ( ComponentTypes.hs, > dist/build/shsh/shsh-tmp/ComponentTypes.o ) > [3 of 5] Compiling Components ( Components.hs, > dist/build/shsh/shsh-tmp/Components.o ) > [4 of 5] Compiling Combinators ( Combinators.hs, > dist/build/shsh/shsh-tmp/Combinators.o ) > [5 of 5] Compiling Shell ( ./Shell.hs, > dist/build/shsh/shsh-tmp/Shell.o ) > Warning: output was redirected with -o, but no output will be generated > because there is no Main module. Name: scc Version: 0.1 Cabal-Version: >= 1.2 Build-Type: Simple License: GPL License-file: LICENSE.txt Copyright: (c) 2008 Mario Blazevic Author: Mario Blazevic Maintainer: blamario(a)yahoo.com Synopsis: Streaming component combinators Executable shsh Main-is: Shell.hs Other-Modules: Foundation, ComponentTypes, Components, Combinators Build-Depends: base, containers, process, readline, parsec Library Exposed-Modules: Foundation, ComponentTypes, Components, Combinators Build-Depends: base, containers

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Re: [Haskell] [Haskell-cafe] Help with polymorphic functions
by Reinier Lamers 08 May '08

08 May '08

Op Thursday 08 May 2008 21:10:08 schreef Wei Yuan Cai: > shift is defined as "a -> Int -> a" It's not. It's defined as "(Bits a) => a -> Int -> a" or something along those lines. So there is a restriction that the type a must be a member of the Bits typeclass. Because "test" is essentially just "shift", its type must also be "(Bits a) => a -> Int -> a". Reinier

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Re: [Haskell] [Haskell-cafe] Help with polymorphic functions
by Bulat Ziganshin 08 May '08

08 May '08

Hello Wei, Thursday, May 8, 2008, 11:10:08 PM, you wrote: > test :: a -> Int -> a > shift is defined as "a -> Int -> a" not exactly ;) this type signature is given inside class Bits, where 'a' isn't a free variable (as in standalone signature declaration), but means 'a' from type class header: class Num a => Bits a where shift :: a -> Int -> a so, this declaration is equivalent to the following standalone one: shift :: (Bits a) => a -> Int -> a from the common sense POV, you can't shift *ANY* type 'a', but only types that belong to the Bits class. so, shift cannot have signature w/o class, and the same remains true for `test` -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Workshop on Generic Programming: Call for Papers (co-located w/ ICFP08)
by Matthew Fluet (ICFP Publicity Chair) 08 May '08

08 May '08

CALL FOR PAPERS Workshop on Generic Programming 2008 Victoria, Canada, 20th September 2008 http://www.comlab.ox.ac.uk/ralf.hinze/wgp2008/cfp.{html,pdf,ps,txt} The Workshop on Generic Programming is sponsored by ACM SIGPLAN and forms part of ICFP 2008. Previous Workshops on Generic Programming have been held in Marstrand (affiliated with MPC), Ponte de Lima (affiliated with MPC), Nottingham (informal workshop), Dagstuhl (IFIP WG2.1 Working Conference), Oxford (informal workshop), Utrecht (informal workshop), and Portland (affiliated with ICFP). Scope ----- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast with normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, class hierarchies, or even programming paradigms. Generic programming techniques have always been of interest, both to practitioners and to theoreticians, but only recently have generic programming techniques become a specific focus of research in the functional and object-oriented programming language communities. This workshop will bring together leading researchers in generic programming from around the world, and feature papers capturing the state of the art in this important emerging area. We welcome contributions on all aspects, theoretical as well as practical, of o adaptive object-oriented programming, o aspect-oriented programming, o component-based programming, o generic programming, o meta-programming, o polytypic programming, o programming with modules, and so on. Submission details ------------------ Deadline for submission: 30th June 2008 Notification of acceptance: 14th July 2008 Final submission due: 28th July 2008 Workshop: 20th September 2008 Authors should submit papers, in PostScript or PDF format, formatted for A4 paper, to Ralf Hinze (ralf.hinze(a)comlab.ox.ac.uk) or Don Syme (Don.Syme(a)microsoft.com) by 30th June 2008. The length should be restricted to 12 pages in standard (two-column, 9pt) ACM. Accepted papers are published by the ACM and will additionally appear in the ACM digital library. Programme committee ------------------- Ralf Hinze (co-chair) University of Oxford Patrik Jansson Chalmers University Andrew Lumsdaine Indiana University Conor McBride University of Nottingham Adriaan Moors Universiteit Leuven Fritz Ruehr Willamette University Tim Sheard Portland State University Don Syme (co-chair) Microsoft Research Todd Veldhuizen University of Waterloo

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Random numbers / monads - beginner question
by Madoc 08 May '08

08 May '08

Hello, I am just learning Haskell. Now, I encountered something that I cannot solve by myself. Your advice will be greatly appreciated. Given a list of numbers, I want to modify each of those numbers by adding a random offset. However, each such modified number shall stay within certain bounds, given by the integers minValue and maxValue. After that, I want to continue computation with the resulting list of type [Int]. But for demonstration, I made a program that just prints out the list: import IO; import Random minValue = 0::Int maxValue = 1000::Int normalize a | a < minValue = minValue | a > maxValue = maxValue | otherwise = a modify a = do offset <- randomRIO(-100::Int, 100) return(normalize(a + offset)) main = putStrLn $ show $ map (modify) [0, 200, 400, 600, 800, 1000] This program will not compile. GHC complains: test.hs:14:18: No instance for (Show (IO Int)) arising from a use of `show' at test.hs:14:18-21 Possible fix: add an instance declaration for (Show (IO Int)) In the first argument of `($)', namely `show' In the second argument of `($)', namely `show $ map (modify) [0, 200, 400, 600, ....]' In the expression: putStrLn $ show $ map (modify) [0, 200, 400, 600, ....] I understand that the result of the modify function is not an Int, as I would like to have it, but instead IO Int, and that cannot be applied to show. (I also did not quite understand why I need those brackets around the return value of the modify value. It won't compile if I leave them out, but I can accept that for now.) I also figured out how to generate a modified list of type [IO Int] and of type IO [Int]. However, I could not find out how to completely get rid of the IO monad and just get a mofied list of type [Int], which is what I really want. Please, do You have any advice for me? I tried for some hours, and now I am really angry at that IO monad that sticks to my pretty integers like glue! Also, any comment on the programming style and how I could achive my goals easier would be appreciated. (I left out comments and function types for the sake of brevity.) Thanks a lot in advance. Madoc. -- View this message in context: http://www.nabble.com/Random-numbers---monads---beginner-question-tp1712438… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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