- Haskell-Cafe - Haskell.org

New Category Theory Intros
by Darrin Thompson 30 Aug '08

30 Aug '08

These category theory intros were new to me. Thought others here might care. http://golem.ph.utexas.edu/category/2008/08/new_structures_for_physics_i.ht… -- Darrin

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Haskell Speed Myth
by Isaac Gouy 30 Aug '08

30 Aug '08

> dons: > (Where I note GHC is currently in second place, though we've not > submitted any parallel programs yet). We might call that the thread-ring effect :-) > Also CC'd Isaac, Mr. Shootout. Isaac, is the quad core shootout > open for business? Should we rally the troops? iirc there was some discussion after the last GHC release about cleaning up the programs to make them less low-level given the improved capabilities of the compiler - I don't think that ever happened, and "low level" seems to be a common complaint against the Haskell programs shown in the benchmarks game. As Simon Peyton-Jones suggested we're certainly open for suggestions: http://groups.google.com/group/fa.haskell/browse_thread/thread/7eb82c689de8… However, we're operating new measurement scripts on both u64q (published) and gp4 (unpublished), and my focus is still on catching up to where we were with measurements from the old scripts, and installing third-party libraries on u64q.

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Re: [Haskell-cafe] Haskell Propeganda
by Richard A. O'Keefe 29 Aug '08

29 Aug '08

On 28 Aug 2008, at 8:34 am, Aaron Tomb wrote: > What type safety buys you, in my mind, is that Nothing is only a > valid value for explicit Maybe types. In cases where you don't use > Maybe, the "null" situation just can't occur. In languages with null > pointers, any pointer could possibly be null. This is not true of Eiffel. The ECMA Eiffel standard has ?T either a void reference or a reference to an instance of T !T a reference to an instance of T T same as !T in ECMA Eiffel; used to be same as ?T I suppose you could call the detachable type ?T an *implicit* Maybe. Needless to say, the switch in semantics of undecorated T helped to fork the Eiffel community...

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How to implement type level type equality?
by Marc Weber 29 Aug '08

29 Aug '08

I'm trying to write a validating XML library. I'm struggling with implementnig the choice alternative. Once piece of the code is Where st is the state representing the subelemnts which may still be attached to the current element. (Basically some tree containing Seq, Or, one or more, 0 or more, 0 or 1) Each xml tag is represented by it's own type. el is the element which should be added. (1): match of types, I'd like to return a C(onsumed) (2): no match, I'd like to return a F(ailure) class Consume st el r | st el -> r -- result is on of C,R,F -- element instance Consume ANY el C instance Consume (Elem el) el C -- (1) instance Consume (Elem el') el (F ExpectedButGot el' el) --(2) Of course this results in: || Functional dependencies conflict between instance declarations: Is there a nice way to implement this type level equality function? Of course I could give an instance for each possible comparison instance EQ TAG_A TAG_A HTrue instance EQ TAG_A TAG_DIV HFalse instance EQ TAG_A TAG_HTML HFalse which would work find but would also be a mess if a xml dtd has many elements. (100 elements means 100 * 100 comparisons = 10.000 *shrug*) I fear this slowing down compilation time a way too much. So my current idea is to assign numbers to all tags and do some type level number comparison. This will work resulting in something like this: data Zero data Succ a class Eq a b c | a b -> c instances: Eq (Succ a) Zero HFalse Eq Zero Zero HFalse Eq Zero (Succ a) HFalse Eq (Eq a b c) => (Succ b) (Succ a) c I want to know wether you know about a more elegant solution. Sincerly Marc Weber

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Re: [Haskell-cafe] Pure hashtable library
by Richard A. O'Keefe 29 Aug '08

29 Aug '08

On 28 Aug 2008, at 9:07 pm, Jules Bean wrote: > Insert for Data.Sequence is log(i) where i is the position of the > insertion; clearly bounded by log(n). toList is O(n) and index is > (at worst) log(i). > > I think the corresponding operations with tries are log(n), Let the key you want to insert have length L. Then insertion into a trie is O(L), independent of the size of the collection. If the "alphabet" the key's elements are drawn from is large, you can use a Ternary Search Tree, and insertion is then O(L.lg B) where B is the branching factor. There are fast Trie construction algorithms which are linear in the total size of the collection, \sum_{i=1}^{n}L_i. The worst case for Data.Sequence is where keys mostly vary at the end, in which case comparisons take O(L) time, and the cost is O(L.lg n), where n is usually much bigger than B. > So, it's all in the constants, isn't it? No.

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Haskell Propeganda
by Thomas Davie 29 Aug '08

29 Aug '08

Today I made an interesting discovery. We all know the benefits of a strong type system, and often tout it as a major advantage of using Haskell. The discovery I made, was that C programmer don't realise the implications of that, as this comment highlights: http://games.slashdot.org/comments.pl?sid=654821&cid=24716845 Apparently, no one realises that a SEGFAULT is a type error, just not a very helpful one. Bob

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ANN: gsl-random 0.1 and monte-carlo-0.1
by Patrick Perry 29 Aug '08

29 Aug '08

Hi everyone, I've started on bindings for the random number generators and random distributions provided by the gsl. The package is available here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gsl-random I've also written a monad and transformer for doing monte carlo computations that uses gsl-random internally. Here is that package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/monte-carlo For a quick tutorial in the latter package, see my blog: http://quantile95.com/2008/08/27/a-monte-carlo-monad-for-haskell/ There is also a more complicated example in the "examples" directory. Currently, only normal, uniform, and poisson random variables are supported. I have no plans to add anything else unless I need it, but I will happily accept patches if someone else is willing to do the work. One thing you may need to watch out for is that gsl-random needs to link with cblas. If your cblas is not called "cblas", you may have to edit "gsl-random.cabal" to get things to work correctly. To use the cblas that comes with the gsl, change "cblas" to "gslcblas". To use ATLAS, change "cblas" to "cblas atlas". Patrick

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Re: [Haskell-cafe] Pure hashtable library
by Richard A. O'Keefe 29 Aug '08

29 Aug '08

Someone wrote: >> >> trie: O(len)*O(width) >> hashed trie: O(len) >> hash: O(len) If "width" here refers to the branching factor of the trie, it's actually O(len.lg(width)), and the width that matters is not the *possible* number of choices but the *actual* number. The great problem with hash tables is devising good hash functions. There is a vast literature about hash tables, but there is very little about how to design good hash functions for anything other than numbers and maybe strings. It would be nice to think that _had__ there been plenty of good advice about constructing good hash functions the Java library implementors would have taken it. As it is, their hashing functions for collections leave much to be desired.

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Galois Tech Talks: Stream Fusion for Haskell Arrays
by Don Stewart 29 Aug '08

29 Aug '08

Just a quick note about next week's Galois Tech Talk. Now that Galois has completed its move into downtown Portland, and a shiny new, centrally located, office space, we're opening up our tech talk series a bit more widely. If you're in Portland, and interested in functional programming and formal methods, drop by! ------------------------------------------------------------------------ Title: Stream Fusion for Haskell Arrays Speaker: Don Stewart Date: Tuesday, July 15th, 10.30am sharp. Location: Galois, Inc. 421 SW 6th Ave. Suite 300 (3rd floor of the Commonwealth Building) Portland, Oregon Abstract: Arrays have traditionally been an awkward data structure for Haskell programmers. Despite the large number of array libraries available, they have remained relatively awkward to use in comparison to the rich suite of purely functional data structures, such as fingertrees or finite maps. Arrays have simply not been first class citizens in the language. In this talk we'll begin with a survey of the more than a dozen array types available, including some new matrix libraries developed in the past year. I'll then describe a new efficient, pure, and flexible array library for Haskell with a list like interface, based on work in the Data Parallel Haskell project, that employs stream fusion to dramatically reduce the cost of pure arrays. The implementation will be presented from the ground up, along with a discussion of the entire compilation process of the library, from source to assembly. About the Galois Tech Talks. Galois (http://galois.com) has been holding weekly technical seminars for several years on topics from functional programming, formal methods, compiler and language design, to cryptography, and operating system construction, with talks by many figures from the programming language and formal methods communities. The talks are open and free. If you’re planning to attend, dropping a note to <dons(a)galois.com> is appreciated, but not required. If you're interested in giving a talk, Don's always looking for new speakers. ------------------------------------------------------------------------

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Haskell symbol ~
by Maurício 28 Aug '08

28 Aug '08

Hi, What does '~' mean in Haskell? I read in haskell.org/haskellwiki/Keywords that “(...) Matching the pattern ~pat against a value always suceeds, and matching will only diverge when one of the variables bound in the pattern is used.” Isn't that true for any variable, due to lazyness? At the same place, I found that example, but wasn't wise enough to figure out what it does: (f *** g) ~(x,y) = (f x, g y) Can you help me understand it? Thanks, Maurício

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Pure hashtable library
by Bulat Ziganshin 28 Aug '08

28 Aug '08

Hello haskell-cafe, solving one more task that uses English dictionary, i've thought: why we don't yet have pure hashtable library? There is imperative hashtables, pretty complex as they need to rebuild entire table as it grows. There is also simple assoc lists and tree/trie implementations, but there is no simple non-modifiable hashes. how should it look: * hashtable is represented as an array of assoc lists: Array Int [(a,b)] * interface to extract data from ht is the same as from assoc list: lookup :: HT a b -> a -> Maybe b * ht may be built from assoc list. we should just know it's size beforehand in order to create Array of reasonable size. constructor also need a hashing function: create :: [(a,b)] -> Int -> (a->Int) -> HT a b given these constraints, it should be just a 10-20 lines of code, and provide much better efficiency than any tree/trie implementations -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Building SDL-image package on Windows
by Garrick Chin 28 Aug '08

28 Aug '08

Hello, I'm trying to build the latest SDL-image package (0.5.2) from Hackage on Windows and encountering problems. These are the steps I've taken so far: 1. Downloaded SDL 1.2.13 developmental library for Mingw32 to E:\SDL-1.2.13, and SDL_image 1.2.6 developmental library for VC8 to E:\SDL_image-1.2.6. 2. Installed SDL package from Hackage, modifying the SDL.cabal according to the included WIN32 readme file and then runghc Setup.lhs configure/build/install 3. Downloaded the SDL-image package from Hackage, modified the SDL-image.cabal file to add the line "Include-Dirs: E:\SDL_image-1.2.6\include\SDL, E:\SDL-1.2.13\include\SDL" so Cabal can find the header files. After doing "runghc Setup.lhs configure", "runghc Setup.lhs build -v" gives me the following output: Creating dist\build (and its parents) Creating dist\build\autogen (and its parents) Preprocessing library SDL-image-0.5.2... Creating dist\build\Graphics\UI\SDL\Image (and its parents) E:\ghc\ghc-6.8.2\bin\hsc2hs.exe --cc=E:\ghc\ghc-6.8.2\bin\ghc.exe --ld=E:\ghc\ghc-6.8.2\bin\ghc.exe --cflag=-package --cflag=SDL-0.5.4 --cflag=-package --cflag=base-3.0.1.0 --cflag=-IE:\SDL_image-1.2.6\include\SDL --cflag=-IE:\SDL-1.2.13\include\SDL -o dist\build\Graphics\UI\SDL\Image\Version.hs Graphics\UI\SDL\Image\Version.hsc E:/ghc/ghc-6.8.2/libHSrts.a(Main.o)(.text+0x7):Main.c: undefined reference to `__stginit_ZCMain' E:/ghc/ghc-6.8.2/libHSrts.a(Main.o)(.text+0x36):Main.c: undefined reference to `ZCMain_main_closure' collect2: ld returned 1 exit status linking dist\build\Graphics\UI\SDL\Image\Version_hsc_make.o failed command was: E:\ghc\ghc-6.8.2\bin\ghc.exe dist\build\Graphics\UI\SDL\Image\Version_hsc_make.o -o dist\build\Graphics\UI\SDL\Image\Version_hsc_make.exe The results of a limited google search suggests that the __stginit_ZCMain linker error has to do with GHC expecting a main function, but I'm not really sure how that works in context of a library.

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building documentation
by Thomas Hartman 28 Aug '08

28 Aug '08

I'm on ubuntu, ghc 6.8.3. I built this using the Generic i386 Linux build at http://www.haskell.org/ghc/download_ghc_683.html How do I build local documentation that matches what I see at http://www.haskell.org/ghc/docs/latest/html/libraries/ -- and am I correct that this is 6.8.3 right now? When I go to file:///usr/share/doc/ghc6-doc/libraries/index.html to browse local docu, I am missing for example Control.Monad.Error.

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Is there GHC 6.8.3 on Ubuntu?
by Rafael Gustavo da Cunha Pereira Pinto 28 Aug '08

28 Aug '08

Is there anyone packing GHC 6.8.3 for Ubuntu Hardy? Thanks -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

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dangling symbolic links
by Nicolas Frisby 28 Aug '08

28 Aug '08

I think I've exhausted my options without catching exceptions. If I have an invalid symbolic link, how can I identify that it exists? (Sorry about the line wrap.) tmp$ ls -l # no tricks up my sleeve, empty directory tmp$ touch foo tmp$ ln -s foo bar tmp$ ls -l total 8 lrwxr-xr-x 1 nfrisby nfrisby 3 Aug 27 23:29 bar -> foo -rw-r--r-- 1 nfrisby nfrisby 0 Aug 27 23:29 foo tmp$ ghc -e 'System.Directory.doesFileExist "bar"' True tmp$ rm foo tmp$ ls -l total 8 lrwxr-xr-x 1 nfrisby nfrisby 3 Aug 27 23:29 bar -> foo tmp$ ghc -e 'System.Directory.doesFileExist "bar"' # it follows the broken link False tmp$ ghc -e 'System.Posix.Files.fileExist "bar"' # the POSIX API also follows False tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap` System.Posix.Files.getFileStatus "bar"' # so does this one POSIX API also follows *** Exception: bar: getFileStatus: does not exist (No such file or directory) tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap` System.Posix.Files.getSymbolicLinkStatus "bar"' # the most successful so far True tmp$ rm bar # but it isn't an existence check... tmp$ ls -l tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap` System.Posix.Files.getSymbolicLinkStatus "bar"' *** Exception: bar: getSymbolicLinkStatus: does not exist (No such file or directory) Is there a way to check for the existence of a symbolic link without testing if getSymbolicLinkStatus raises an exception? This is with Darwin Kernel Version 8.11.1, GHC 6.8.2, directory-1.0.0.0, and unix-2.3.0.0. Thanks.

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xmonad on the openmoko mobile phone
by Don Stewart 28 Aug '08

28 Aug '08

Haskell fans might be impressed by the good work of Joachim Breitner, who got xmonad running on his openmoko phone, http://www.joachim-breitner.de/blog/archives/300-Xmonad-on-my-mobile-phone.… You can see a photo here, http://galois.com/~dons/images/openmoko-nomeata.jpg Haskell on the iphone next? -- Don

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problem with cabal for syb-with-class
by Andrew U. Frank 28 Aug '08

28 Aug '08

i tried to install wxGeneric and need syb-with-class. i got the package from hackage. configure runs fine, but when i build i get: Data/Generics/SYB/WithClass/Instances.hs:11:7: Could not find module `Data.Array': it is a member of package array-0.1.0.0, which is hidden but array-0.1.0.0 is installed, as shown later. what can be wrong? why is an installed package complained about as hidden? thanks for help! andrew frank@bernH:~/haskellSources/packages/syb-with-class-0.3$ ghc-pkg describe array name: array version: 0.1.0.0 license: BSD3 copyright: maintainer: libraries(a)haskell.org stability: homepage: package-url: description: This package defines the classes @IArray@ of immutable arrays and @MArray@ of arrays mutable within appropriate monads, as well as some instances of these classes. category: author: exposed: True exposed-modules: Data.Array Data.Array.Base Data.Array.Diff Data.Array.IArray Data.Array.IO Data.Array.MArray Data.Array.ST Data.Array.Storable Data.Array.Unboxed hidden-modules: Data.Array.IO.Internals import-dirs: /usr/lib/ghc-6.8.2/lib/array-0.1.0.0 library-dirs: /usr/lib/ghc-6.8.2/lib/array-0.1.0.0 hs-libraries: HSarray-0.1.0.0 extra-libraries: extra-ghci-libraries: include-dirs: includes: depends: base-3.0.1.0 hugs-options: cc-options: ld-options: framework-dirs: frameworks: haddock-interfaces: /usr/share/doc/ghc6-doc/libraries/array/array.haddock haddock-html: /usr/share/doc/ghc6-doc/libraries/array f

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Associative Commutative Unification
by John D. Ramsdell 28 Aug '08

28 Aug '08

I'd like to write an obviously correct implementation of a unifier, a program that when given two terms, finds a substitution that makes the two terms equal. The phrase "obviously correct" is meant to imply that the clarity of the code trumps efficiency. As near as I can tell, high performance unifiers are full of side-effects, and achieving the same performance without side-effects in Haskell is difficult or impossible. In contrast, it is easy to write obviously correct Hasklell implementations of unifiers for freely generated term algebras. One can use Lawrence Paulson's code in ML for the Working Programmer as a template or follow Martelli and Montanari's simple set of rules. My problem is one of my operators is multiplication, which is associative and commutative. These two properties make unification much more difficult. Mark Stickel described a complete unification algorithm for this problem, but the task of translating his description into an obviously correct Haskell program appears to be difficult. For example, the algorithm requires the generation of the basis of solutions to linear homogeneous diophantine equations. I haven't located an algorithm for this part yet. If you have experience implemented equational unification in Haskell, please share it. John

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Problem building the plugins package
by Emmanuel 28 Aug '08

28 Aug '08

Hello I am having troubles building the plugins package : manu:~/Desktop/tmp manu$ cabal install plugins Resolving dependencies... cabal: cannot configure plugins-1.2. It requires ghc >=6.8 There is no available version of ghc that satisfies >=6.8 I am on a Mac PPC (OS X 10.4) with ghc-6.8.2 and Cabal-1.4.0.1 so the error message is puzzling... Can anyone help ? I'd like to install Lambdabot and plugins is one of the dependencies... Thanks Manu

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timer_create revisited
by Brandon S. Allbery KF8NH 28 Aug '08

28 Aug '08

I'm trying to build GHC 6.8.2 (6.8.3 once I get all this nailed down...) from an old bootstrap ghc on SuSE 9.3-64 (yes, I know) because the 6.6.1 and newer binary tarballs for amd64 Linux doesn't work with the "timer_create" issue. The problem is, having built a shiny new 6.8.2 both stage1 and stage2, the result works but compiled programs have the "timer_create" problem. (??) At this point I'm stymied. Suggestions, other than "upgrade" (not currently possible due to commercial software support and timing issues)? -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH

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ANNOUNCE: Wired 0.1.1
by Emil Axelsson 28 Aug '08

28 Aug '08

Hello, This is to announce the first release of the hardware description library Wired. Wired can be seen as an extension to Lava that targets (not exclusively) semi-custom VLSI design. A particular aim of Wired is to give the designer more control over the routing wires' effects on performance. The only working backends in this version are simulation and verification (through Lava), and generation of postscript layouts. Soon, there will also be static timing analysis and DEF file generation. The DEF format is accepted by most tools for physical design. Wired is available from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Wired or using Darcs: darcs get http://www.cs.chalmers.se/~emax/darcs/Wired/ There is also a homepage at: http://www.cs.chalmers.se/~emax/wired/index.html Comments, questions, patches are welcome. Cheers, / Emil

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Re: [Haskell] Another First course in Haskell
by Johannes Waldmann 27 Aug '08

27 Aug '08

Piyush P Kurur wrote: ( http://article.gmane.org/gmane.comp.lang.haskell.general/16390 ) > I am planing a haskell based functional programming course. > It is supposed to be a first course and I intend to show how > real world applications can be built quite easily in haskell. > Any feed back is really welcome. Is it a first course in programming, or in functional programming? Either way, I recommend focus on "data" and then "class/instance", i.e. have the students use algebraic data types right from the beginning (*). Another idea for teaching is to introduce the language by having the students use standard libraries (e.g. Data.Map), also right from the start. So they are forced to read type signatures etc. (**) (*) that's the main problem I see with Hutton's book http://www.cs.nott.ac.uk/~gmh/book.html : it has "Declaring types and classes" as chapter 10 (of 13 total). I think that's way off - and it leaves readers (students) with the impression that declarative programming basically deals with (functions on) lists. This may have been true in the 70s/80s (LISP, Prolog), but it certainly shouldn't be true today. Recall the proverb "Get your data structures correct first, and the rest of the program will write itself." (David Jones, cited in John Bentley: More Programming Pearls) I think this is independent of language and paradigm. (**) again, Hutton's book does not contain a single "import" declaration in the programming examples (did not check fully, but got this impression while browsing). Yes , Data.* is not Standard Haskell(98) and that's probably why he avoided it but the result diametrically contradicts everyday programming experience where the typical application program (in any language) is just some glue between library functions that do 90 percent of the actual work. Sure, a student programmer must be able to write a stand-alone bubble/quick/mergesort but it is equally (if not more) important that he knows how to (1) find and (2) call a sorting routine in any given programming environment. (So, have your students use http://www.haskell.org/hoogle/ ) Best regards, J.W.

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apparent minor bug in "Getting started" tutorial at "Haskell Hacking: a journal of Haskell programming"
by Benjamin L.Russell 27 Aug '08

27 Aug '08

This is just a minor documentation bug report, but I tried following the instructions in the "Getting started" tutorial at "Haskell Hacking: a journal of Haskell programming" (http://cgi.cse.unsw.edu.au/~dons/blog/2006/12/16#programming-haskell-intro) for GHCi 6.8.3 on Windows XP Professional (Service Pack 2), as follows: >You can compile this code to a native binary using GHC, by writing in a source file: > > main = putStrLn "G'day, world!" > >and then compiling the source to native code. Assuming your file is A.hs: > > $ ghc A.hs > >This produces a new executable, ./a.out (a.out.exe on windows), which you can run like any other program on your system: > > $ ./a.out > G'day, world! However, this produced the following files, instead: A.hi A.o main.exe main.exe.manifest There was no a.out file, and running A.o popped up a Windows dialog box asking me to specify which application to run the program with. So, I ran $ ghc --help and found the following documentation: >To compile and link a complete Haskell program, run the compiler like >so: > > ghc --make Main > >where the module Main is in a file named Main.hs (or Main.lhs) in the >current directory. The other modules in the program will be located >and compiled automatically, and the linked program will be placed in >the file `a.out' (or `Main.exe' on Windows). > >[...] > >Given the above, here are some TYPICAL invocations of ghc: > > # compile a Haskell module to a .o file, optimising: > % ghc -c -O Foo.hs Running $ main.exe produced the desired result: >G'day, world! Would it be possible to update the documentation to reflect the need to enter $ main.exe after compilation instead of $ a.out ? Thank you. -- Benjamin L. Russell

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Re: [Haskell-cafe] Re: [Haskell] Top Level <-
by Adrian Hey 27 Aug '08

27 Aug '08

Lennart Augustssom wrote: > Since at some point you have to interface with the hardware you are > forced to obey whatever convention is used for interrupts etc. At that > point you may very well have to use global variables. But you can > quickly abstract away from that in stay in the safe land without globals. BTW, did you notice that the non-hosted driver API example I put on the wiki page doesn't use "globals" either :-) The two device handles are at the top level (are "globals" as you would say), but the driver code takes these as an argument so doesn't care if they're top level or not. If I don't have the device handles at the top level or some means to get them from the top level then I have no alternative but to export createDeviceHandle either directly to the "user level" API (really bad!) or to some other bit of higher level system code that can be trusted not to create 2 or more handles for the same device (and no handles for non-existant devices). Let's assume it's that latter. In the simple case where it is known at compile time that there are exactly 2 devices in the system at known base addresses, can you explain how the higher level bit of the system guarantees that user level application code will only ever have access to 2 different device handles in total (one for each device), no matter what? How does it solve this problem in the more complex complex case where hardware must be probed somehow to discover how many devices there are and where they are? All without using any global variables please. Also, assuming you succeed, please explain what advantages or extra safety your solution provides over a solution which does use global variables. The obvious solution seems to be to have this code present this function to the user level API.. getAvailableDeviceHandles :: IO [DeviceHandle] Which shouldn't be hard to implement in either case, except for the fact IO state "getters" can't be implemented at all without top level mutable state or runOnce primitives or something like that (AFAICS). newAvailableDeviceHandles perhaps? I guess that could come in handy if the user code decides it doesn't like the old ones for some reason :-) Regards -- Adrian Hey

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best runProcess solution to work with windows and linux
by Andrew U. Frank 27 Aug '08

27 Aug '08

i use System.POSIX.IO to run a process and access the handles (after due transformation) to get the values back. this solution is unfortunately not portable and works only on unix (or cygwin) but not for plain windows. there seems to be a somewhat comparable package in system.win32.process. is there a solution independent of OS? what is the best approach to use to run a process and read the result back which works in both unix and windows? any suggestion highly appreciated! andrew

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Re: [Haskell] Top Level <-
by Adrian Hey 27 Aug '08

27 Aug '08

(Moving to Haskell cafe) Edward Kmett wrote: > On Sun, Aug 24, 2008 at 7:12 PM, Ashley Yakeley <ashley(a)semantic.org> wrote: > >> Is there any interest in implementing a top level "<-" to run monadic code? >> > > This is actually implemented in jhc. See the 'top level actions' section of > http://repetae.net/computer/jhc/manual.html Gosh! I was always quite impressed by Johns determination to write a Haskell compiler and by his self discipline in resisting the temptation to fix everything that was wrong with Haskell and keep to standards :-) I implemented my own ACIO monad a while ago (which is of course quite useless without top level <- bindings) and it turned out that there was quite a lot that could go in here. The only problem seemed to be that some things that seemed perfectly reasonable to create via ACIO had *IO* finalisers associated with them, which didn't feel right to me. But if you think about how finalisers get run I'm inclined to think we should insist that they are ACIO too. Regards -- Adrian Hey

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darcs weekly news #1
by Eric Kow 27 Aug '08

27 Aug '08

Hi everybody, I thought it would be useful if we got back into the habit up summarising our weekly darcs activities. This is the first entry of what I hope to be Darcs Weekly News. Note that I have also Bcc'ed the Haskell Cafe; which I will not be doing everytime, but just this once :-) News and discussions -------------------- hacking sprint (25/26 October) We are now planning three sites for the upcoming darcs hacking sprint: Brighton (moved from Cambridge), Paris and Portland. More news as we finalise the venues in the next two weeks! performance benchmarking Eric is working on integrating performance regression testing into the darcs buildbot. The progress is slow but steady! darcs 2 real world comparison Jason analyses a comparison of darcs push between 1.0.9 and 2.0.2. http://blog.codersbase.com/2008/08/21/darcs-2-real-world-push-performance-e… darcs weekly news Most of darcs weekly news is automated, but we still need human editors! To help out, darcs get http://code.haskell.org/darcs/darcs-news Issues resolved in the last two weeks (5) ----------------------------------------- * issue115 (Dmitry Kurochkin) match patches touching given files. http://bugs.darcs.net/issue115 * issue823 (Dmitry Kurochkin) do not exit on keyboard interrupt when getting patches. http://bugs.darcs.net/issue823 * issue936 (Dmitry Kurochkin) fix type witnesses configure check. http://bugs.darcs.net/issue936 * issue950 (David Roundy) fix fix_filepath to work with --repodir (and add test demonstrating this). http://bugs.darcs.net/issue950 * issue995 (Dmitry Kurochkin) changes --context : {--human-readable,--xml-output} have no effect. http://bugs.darcs.net/issue995 Patches applied in the last two weeks (69) ------------------------------------------ 2008-08-25 Jason Dagit minor refator to get_extra improve comments 2008-08-25 Eric Kow Same ChangeLog entries since 2.0.2 Some more globally ignored changes. 2008-08-24 David Roundy Simplify filepath handling, cutting lots of hardly-used code. don't bother computing path when checking prereqs (since we now can handle looking at beginning/ending working directories). resolve issue950: fix fix_filepath to work with --repodir (and add test demonstrating this). eliminate fix_flag. add new framework for ensuring that certain arguments are converted to absolute paths. make Darcs.Lock functions accept FilePathLike arguments. refactor maybeMkSubPath very slightly. refactor repoPath very slightly. make makeAbsolute behavior match comment. 2008-08-22 Dmitry Kurochkin Fix makeAbsolute to work with '../foo' paths. 2008-08-22 David Roundy move withCurrentDirectory, withTempDir and withPermDir rewrite mkAbsolutePath to be safe. 2008-08-22 Eric Kow Changelog (ignore 'Add a test entries') 2008-08-22 David Roundy resolve conflicts. 2008-08-19 Dmitry Kurochkin Resolve issue936: fix type witnesses configure check. Use forkIO in URL module as suggested by Simon Marlow. Remove HTTP.copyUrl, integrate it to URL module. More URL module refactoring. 2008-08-22 Eric Kow Canonize Nathaniel Filardo and Simon Marlow. Add test case for issue966 (from Dan Pascu's bug report) 2008-08-21 David Roundy remove trailing whitespace. 2008-08-21 Dmitry Kurochkin Documentation for match touch primitive. Resolve issue115: match patches touching given files. 2008-08-22 Eric Kow Remove unused FileSystem module. 2008-08-20 David Roundy fix type witnesses in with_selected_patch_from_repo. clean up bugs functions (eliminate darcsBug.h). 2008-08-19 Jason Dagit Fix a bug with incorrectly specified with_selecte_patch_from_repository. 2008-08-19 Dmitry Kurochkin Remove HTTP.exists, use Autoconf.have_HTTP instead. 2008-08-19 David Roundy fix improper use of bug in HTTP. 2008-08-19 Dmitry Kurochkin Do not import HTTP module in Darcs.Bug, use bug and debugFail for error reporting in HTTP module. 2008-08-19 David Roundy fix incompatibility with ghc 6.6. make scan_bundle create a lazy patch bundle. resolve conflicts with Darcs.Ordered change. 2008-08-15 Jason Dagit replace separate_middle_last_from_first and separate_last_from_first_middle with get_choices correct a bug in with_selected_patches_from_repository refine type witnesses in SelectChanges make WhatsNew work with type witnesses major refactor of SelectChanges to work with type witnesses 2008-08-16 nwf(a)cs.jhu.edu Move Darcs.Patch.Ordered to Darcs.Ordered since it isn't patchy 2008-08-19 Simon Marlow Fix use of threadWaitRead on Windows Fix Windows build 2008-08-17 Dmitry Kurochkin URL module refactoring. Do not compile curl support if libwww is enabled. URL.hs: always import debugFail, again. URL.hs: call debugFail when download fails. URL.hs: debug messages. Spacing in Darcs/Commands/Changes.lhs Rename catchInt to catchInterrupt, better message when get is interrupted. Resolve issue995: changes --context : {--human-readable,--xml-output} have no effect. 2008-08-18 Eric Kow Add test for issue1017 (as suggested by Bjorn Bringert) 2008-08-19 David Roundy don't print "Wrote patch to -" when writing patch to stdout. always send with context. 2008-08-18 Eric Kow Tidy up known failing shell tests. Tidy up failing test for issue1013. Move hidden conflicts bug to tests directory. Add failing test for issue1012 (Simon Marlow). 2008-08-15 Dmitry Kurochkin Resolve issue823: do not exit on keyboard interrupt when getting patches. 2008-08-14 David Roundy fix buggy comments in bugs/identical-patches.sh. 2008-08-13 Eric Kow Add Ian's identical-patch test case. 2008-08-13 Dmitry Kurochkin URL.hs: store only URL in waitToStart queue. 2008-08-14 Eric Kow Add (failing) test for issue944. 2008-08-13 nwf(a)cs.jhu.edu Split Cache mostly out of Darsc/Repository/Prefs into its own file (take 2) 2008-08-13 Jason Dagit remove a few unsightly functions 2008-08-13 Dmitry Kurochkin Fix URL module bug with pipelining enabled. Minor change to URL module. Enable pipelining by default, add --disable-pipelining option (issue838). -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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contributing to standard library
by Tim Newsham 27 Aug '08

27 Aug '08

Like everyone else who has used Haskell for a while, I'm accumulating functions which I feel should have already been in the standard libraries. What's the normal path to contributing functions for consideration in future standard libraries? Is there some experimental standard lib that we can contribute to to "try out" for the big league? Here are some functions: http://www.thenewsh.com/%7Enewsham/x/machine/Missing.hs Tim Newsham http://www.thenewsh.com/~newsham/

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ANN: First Monad Tutorial of the Season
by Hans van Thiel 27 Aug '08

27 Aug '08

Hello All, I'm proud to announce the first monad tutorial of the new season. It's under the Wiki permissive licence, but the web page has some clip art, so 'The Greenhorn's Guide to becoming a Monad Cowboy' is on http://www.muitovar.com/monad/moncow.xhtml Best Regards, Hans van Thiel

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unsafeInterleaveIO, lazyness and sharing
by Wolfgang Jeltsch 27 Aug '08

27 Aug '08

Hello, Haskell is non-strict but not necessarily lazy. So it’s possible that an expression is reduced to WHNF although it is not used yet. Could this “early reduction” also happen to outputs of unsafeInterleaveIO actions (which might trigger the action too early)? While I’d expect those outputs to be evaluated lazily (reduced as late as possible), I cannot find anything in the docs that guarantees this. In addition, I’d like to know whether unsafeInterleaveIO outputs are guaranteed to be evaluated at most once so that the “interleaved action” is executed at most once. Again, I suppose that this is the case while I cannot find a guarantee for it. Best wishes, Wolfgang

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Re: [Haskell] Re:Fwd: Haskell job opportunity: Platform Architect at
by John Meacham 27 Aug '08

27 Aug '08

On Wed, Aug 20, 2008 at 03:17:14PM -0700, Jason Dusek wrote: > What is your company going to do? What sort of dot-com attitude is that? Your company does whatever the buzzword that the venture capitalist you are currently talking to is enthralled with. :) 'monadic B2B ultra-wideband catamorphic connection oriented infospherespace' John -- John Meacham - ⑆repetae.net⑆john⑈

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String to Double conversion in Haskell
by Daryoush Mehrtash 27 Aug '08

27 Aug '08

I am trying to convert a string to a float. It seems that Data.ByteString library only supports readInt. After some googling I came accross a possibloe implementation: http://sequence.svcs.cs.pdx.edu/node/373 My questions are: a) is there a standard library implementation of string -> Double and float? b) Why is it that the ByteString only supports readInt? Is there a reason for it? Thanks, Daryoush Mehrtash

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Re[2]: [Haskell] Top Level <-
by Bulat Ziganshin 27 Aug '08

27 Aug '08

Hello Derek, Tuesday, August 26, 2008, 8:14:21 PM, you wrote: >> but from my POV it's important to push this feature into haskell >> standard > Haskell should be moving -toward- a capability-like model, not away from > it. what you mean by "capability-like model"? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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OpenGL's VBO with Haskell
by Twinside 27 Aug '08

27 Aug '08

Hi Haskell list, Today I'm turning to you for the use of VBO (Vertex Buffer Object) in Haskell. I seem to be able to create one without any problem using the following code : ------------------------------------------------------ vboOfList :: Int -> [Float] -> IO BufferObject vboOfList size elems = let ptrsize = toEnum $ size * 4 arrayType = ElementArrayBuffer in do [array] <- genObjectNames 1 bindBuffer arrayType $= Just array arr <- newListArray (0, size - 1) elems withStorableArray arr (\ptr -> bufferData arrayType $= (ptrsize, ptr, StaticDraw)) bindBuffer ArrayBuffer $= Nothing reportErrors return array ------------------------------------------------------ However the problem arise when I try to draw primitives using this vbo : ------------------------------------------------------ displayVbo buff size = do let stride = toEnum sizeOfVertexInfo vxDesc = VertexArrayDescriptor 3 Float stride $ offset 0 colors = VertexArrayDescriptor 4 Float stride $ offset 12 texCoo = VertexArrayDescriptor 2 Float stride $ offset (12 + 16) filt = VertexArrayDescriptor 4 Float stride $ offset (12 + 16 + 8) bindBuffer ArrayBuffer $= Just buff arrayPointer VertexArray $= vxDesc arrayPointer ColorArray $= colors arrayPointer TextureCoordArray $= texCoo arrayPointer SecondaryColorArray $= filt drawArrays Quads 0 size bindBuffer ArrayBuffer $= Nothing ------------------------------------------------------ Nothing is displayed on screen. As you can see, my VBO contain interleaved data : - 3 float for the vertex - 4 for the color - 2 for the texture coordinate - 4 for the secondary color) The 'offset' function has type Int -> Ptr Float, and is used to forge a pointer from an Int, to mimic the C way of using VBO. As far as I've checked, the values in my list for VBO generation are valid and well displayed using other techniques. So is there a workaround other method for my solution, preferably by keeping my data interleaved? Secondly, is there any sample for advanced features like VBOs in Haskell? Regards, Vincent

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Haskell Speed Myth
by Thomas Davie 26 Aug '08

26 Aug '08

Lo guys, I thought you'd like to know about this result. I've been playing with the debian language shootout programs under OS X, looking at how fast Haskell code is compared to C on OS X, rather than linux. Interestingly, Haskell comes out rather better on OS X than it did on Linux. Here's my results (times in seconds): C Haskell Relative speed Inverse Binary Trees 6.842 1.228 0.179479684302835 5.57166123778502 Fannkuch 5.683 15.73 2.76790427591061 0.361284170375079 Mandelbrot 1.183 2.287 1.93322062552832 0.517271534761697 nbody 10.275 16.219 1.57849148418491 0.633516246377705 nsieve 0.167 0.253 1.51497005988024 0.660079051383399 nsieve-bits 0.471 0.713 1.51380042462845 0.660589060308555 partial sums 1.047 1.313 1.25405921680993 0.797410510281797 pidigits 1.238 1.4 1.13085621970921 0.884285714285714 recursive 1.554 3.594 2.31274131274131 0.432387312186978 spectral-norm 27.939 19.165 0.685958695729983 1.45781372293243 threadring 91.284 1.389 0.0152162481924543 65.719222462203 ------------------------------------------------------------------------- Averages 1.35333620432893 0.738914688605306 Some notes: Hardware: 2Ghz Core2Duo, enough ram to not worry about paging Some programs are not included, this is because the C code produced compile errors. The Haskell code appears to be portable in *all* cases. The average slowdown for running Haskell is only 1.3 times on OS X! That's pretty damn good. I'm sure some people will say "yeh, but you have to optimise your code pretty heavily to get that kind of result". Interestingly, the programs that have the biggest speed advantage over C here are also the most "naïvely" written ones. The thing that seems to make C slower is the implementation of malloc in OS X. This has a couple of implications, first, if apple replaced the malloc library, it would probably push the result back to the 1.7 times slower we see under Linux. Second, Fannkuch can probably be optimised differently for Haskell to look even better -- at the moment, the haskell code actually uses malloc! Finally, that threading example... WOW! 65 times faster, and the code is *really* simple. The C on the other hand is a massive mess. Bob

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Valid Haskell characters
by Maurício 26 Aug '08

26 Aug '08

Hi, In Haskell reference, I see the following definitions: uniWhite -> any Unicode character defined as whitespace; uniSmall -> any Unicode lowercase letter; uniLarge -> any uppercase or titlecase Unicode letter; uniSymbol -> any Unicode symbol or punctuation. Where do I get lists for those characters? My first attempt was to check: http://unicode.org/Public/UNIDATA/UnicodeData.txt and consider large anything marked as CAPITAL and small anything marked as SMALL. I didn't know what to guess about the symbols. Am I using the right reference? How can I recognize (or get a list of) valid uppercase and lowercase unicode letters, as well as symbols and punctuation? Thanks for your help, Maurício

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Re: [Haskell-cafe] Valid Haskell characters
by Richard A. O'Keefe 26 Aug '08

26 Aug '08

On 26 Aug 2008, at 3:42 pm, Deborah Goldsmith wrote: > All characters with general category Lu have the property Uppercase, > but the converse is not true. It depends on what the OP wants to do with the information. For example, Unicode Standard Annex 31, http://www.unicode.org/reports/tr31/tr31-9.html is defined in terms of the General Character classification, *not* in terms of the binary properties "Upper", "Alpha", &c. When the Haskell report says uniSmall -> any Unicode lowercase letter uniLarge -> any uppercase or titlecase Unicode letter it is really unclear what definition is meant: are we talking about characters in general category Lu or Lt, or are we talking about characters with the Uppercase property? Since it's _identifiers_, I'd expect UAX#31 to apply, so it should be general category. The specification of the Char module is similarly ambiguous. Since this is *not* about identifiers, I suppose this time the Other_Uppercase characters might well be included. It would be nice to have this spelled out clearly somewhere not too far from the Report on haskell.org.

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Re: [Haskell-cafe] Valid Haskell characters
by Richard A. O'Keefe 26 Aug '08

26 Aug '08

On 26 Aug 2008, at 1:31 pm, Deborah Goldsmith wrote: > You can't determine Unicode character properties by analyzing the > names of the characters. However, the OP *does* have a copy of the UnicodeData...txt file, and you *can* determine the relevant Unicode character properties from that. For example, consider the entry for space: 0020;SPACE;Zs;0;WS;;;;;N;;;;; ^^ The Zs bit says it's a white space character (Zs: separator/space, Zl: separator/line, Zp: separator/paragraph). Or look at capital A: 0041;LATIN CAPITAL LETTER A;Lu;0;L;;;;;N;;;;0061;^ ^^ The Lu bit says it's a L(etter) that is u(pper case). Upper case: Lu, lower case: Ll, title case: Lt, modifier letter: Lm, other letter: Lo, digit: Nd, ... If memory serves me correctly, this is explained in the UnicodeData.html file, under a heading something like Normative Categories.

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can the default instances in GHC be recompiled with overlap?
by Jason Dusek 26 Aug '08

26 Aug '08

Per the GHC manual section on instance overlap: If an instance declaration is compiled without -XOverlappingInstances, then that instance can never be overlapped. This could perhaps be inconvenient. It is inconvenient for certain things. If I want to declare a special `instance Show [MyType] where...` I am out of luck. However, the solution need not involve a change to the way instances are handled -- if all the `GHC.*` instances were compiled with overlapping instances, I'd be able to declare my instance. Is there a substantial barrier, either theoretical or practical, to recompiling GHC this way? -- _jsn |...GHC manual section...| http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensio…

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Prototype of a syntax reference
by Maurício 26 Aug '08

26 Aug '08

Hi, I'm trying to make a syntax reference in the form of source code. It's not ready, but if someone shares the same ideas I could use some help. (Should I put this on a wiki? Where?) My “design principles” are: • It should contain just pieces of uncommented code. The idea is not to use it as a fast tutorial, but as a reminder of how to write all kinds of things, and solve all questions of type “is this allowed?”; • It should be small, and fit on a printed A4 page; • It should show the complete syntax of everything, not the most common. For instance, ‘case of’ should show the use of guards; • It should be an example of valid code, not good one. The idea is to show what can be done, not what should :) • It should use expanded code, not identation rules. Replacement of identation for code (like {} etc.) have simple rules, and the proper way to ident can be deduced from expanded code. Sometimes this is important if we are trying to solve syntax errors; • It should use Unicode. It's nice to know which kind of Unicode characters can actually be used; • It should use no predefined types or classes except Bool. I’ll write a Prelude code reference if this first attempt go right. So I came up with the weird code below. It should contain a lot more, and be more dense (more syntax examples per lines of code), but it's already usefull for a begginer like me. What do you think? Best, Maurício module Ça (Exèmplo(Åwirù,Øwet'Л,Øwet'И),aҝҧү,Clááá) where { class Clááá ú where { (⊗) :: ú -> ú -> ú; τAmber :: ú -> ú; τAmber a = a ⊗ a; }; data D١ = U1 | U2 | U3; data D٢ = Vú1 | Vú2 | JustVú; data D٤ = Opção | OutraOpção; data Exèmplo = Åwirù | Øwet'Л D٤ | Øwet'И D٢ Exèmplo; osmesmos :: D٤ -> D٤ -> Bool; osmesmos Opção Opção = True; osmesmos OutraOpção OutraOpção = True; osmesmos _ _ = False; aҝҧү = (Øwet'И Vú2 aҝҧү) ⊗ Åwirù; instance Clááá Exèmplo where { Åwirù ⊗ _ = Åwirù; a@(Øwet'Л b) ⊗ x = case x of { Åwirù -> a; y@(Øwet'Л o) | (osmesmos o Opção) -> a | otherwise -> Øwet'И Vú1 y; y@(Øwet'И _ _) -> y ⊗ a }; a@(Øwet'И Vú1 _) ⊗ _ = a; a@(Øwet'И Vú2 x) ⊗ _ = x; a@(Øwet'И JustVú _) ⊗ y = y; } }

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Re: [Haskell-cafe] Haskell Propeganda
by Niels Aan de Brugh 26 Aug '08

26 Aug '08

Christopher Lane Hinson wrote: >> Here's an error the Haskell run-time system might throw: >> *** Exception: Prelude.head: empty list >> (or whatever) >> >> So now what? Action plan = []. > > rgrep " head " . > > Lists 17 items for three projects I've been working on summing to > 10000 lines of haskell. Use listToMaybe or pattern matching and > -Wall, and raise an explicit (error "with explanation"), which is all > good practice in the C world as well. Please, don't make undocumented > use of partial functions in serious code. You're absolutely right, and the compiler can warn the programmer for such mistakes. However, I've found that analysing the run-time behaviour/errors (if they do occur) in a Haskell program to be harder than in a language like C(++) which has many very mature engineering tools available. No doubt this is a matter of time and money, not which language is better suited for "real work". Regards, Niels

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ANN: The Monad.Reader - Issue 11
by Wouter Swierstra 25 Aug '08

25 Aug '08

I am pleased to announce that a new issue of The Monad.Reader is now available: http://www.haskell.org/haskellwiki/The_Monad.Reader Issue 11 consists of the following three articles: * David F. Place How to Refold a Map * Kenneth Knowles First-Order Logic a la Carte * Douglas M. Auclair MonadPlus: What a Super Monad! The Monad.Reader is a quarterly magazine about functional programming. It is less formal than a journal, but a bit more enduring than a wiki page or blog post. If you'd like to write something for the next issue of The Monad.Reader, please get in touch. I haven't fixed the deadline for the next issue just yet. Expect a deadline early 2009. Wouter

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Re: [Haskell] Top Level <-
by Duncan Coutts 25 Aug '08

25 Aug '08

This topic came up in #haskell this evening... On Sun, 2008-08-24 at 16:12 -0700, Ashley Yakeley wrote: > 1. Global mutable state. For instance, here's the count variable for > Data.Unique rewritten: > > uniqSource :: MVar Integer > uniqSource <- newMVarTL 0 > > Isn't that much nicer? > <http://haskell.org/haskellwiki/Top_level_mutable_state> It's nicer syntax but it's still not true. There's still no such thing as a global variable. There's always a scope. In this case what scope are we looking for? Process scope? Only one instance of uniqSource per process? If so, it's not right. We can link in multiple copies of a package and thereby end up with multiple instances (this really happens, it's not a far fetched scenario). So uniqSource is a package-name/version scope mutable variable. To get the right thing for the annoying C libs that have 'global' init and finalise functions you need something else. Not actually process scope, that's too wide. You need exactly the same scope as the system linker is using, so that we get one variable per instance of the C library linked into the process. Consider a process using several dlls where each one links to a C lib that needs 'global' initialisation, we must have exactly one 'global' var instance per dll in this case because that's the linker namespace scope. The scope you need depends on the application. A language extension like this is likely to only cover package-name/version scope, not scopes like thread, OS thread, rts instance, linker, process, user account, OS, subnet, interweb, planet etc. So in practise, what scopes do we often need, and does package-name/version scope correspond to many of those use cases? Duncan

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ANN: Mueval 0.5.1, 0.6, 0.6.1, 0.6.2, 0.6.3, 0.6.4
by Gwern Branwen 25 Aug '08

25 Aug '08

Evening folks. So it's that time again, to do a Mueval announcement! This time I'd like to announce version 0.6.4, & 0.6.3. And 0.6.2. And 0.6.1. And 0.6. And 0.5.1. These releases have some nice stuff to them; perhaps the most interesting aspect is that I've carried through on my threats^Wpromises, and Lambdabot in #haskell now uses Mueval. GETTING All the stuff from the previous ANNs still apply here: you can get it at <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>, do a 'darcs get --lazy http://code.haskell.org/mubot/', cabal-install mueval, and so on. DEPENDENCIES 0.6.4 does add an additional dependency, on haskell-src-exts, for use in some experimental parsing code, so you'll now need that in addition to Hint, utf8-string, and show. (Upgrading Hint is mandatory, utf8-string unnecessary, and show nice but certainly not necessary.) BUILDING Same as usual. CHANGES 0.5.1 * SmallCheck support 0.6 * A new option, --loadfile, which loads a given *.{l}hs file with a module and makes its function available for evaluation. This is a complex option; see the README. * Cleaner output, thanks to a needless show call sjanssen identified. 0.6.2 * Speed improvements (shorter timeouts, optimizations) * Mueval imports many more modules by default, so one can freely use standard functions from Control.Monad, for example; this also brings with it many test examples from #haskell. * experimental --noimports flag, to disable default imports (such as the above, and also of the Prelude). This was motivated by Lambdabot's Caleskell, but I'm not sure why it doesn't interact well with --loadfile (and so doesn't work with Lambdabot). 0.6.3 * Saizan contributed some significant improvements to error reporting and thread handling, so the infamous time-out errors are replaced by normal errors more reminiscent of GHCi. 0.6.4 * Fixed an issue with lazy printing of results * Exceptions are now caught and printed more prettily; again, thanks to Saizan * Forced a dependency on the latest Hint; this fixes an error where one could successfully evaluate: bash-3.2$ mueval -e '1 + 1 {- addition example -}' 2 but not: bash-3.2$ mueval -e '1 + 1 -- addition example' * Added a --rlimits option. I decided that the POSIX resource limits were causing too many people problems. So now non-time resource limits are disabled unless specifically requested with --rlimits. * mmorrow contributed some experimental parsing patches intended to catch subtle invocations of dangerous functions. If haskell-src-exts is too burdensome a dependency, Mueval/Context.hs and mueval.cabal can be easily edited to remove the dependency. KNOWN ISSUES * Qualified imports do not work. That is, one cannot do $ mueval -e 'M.map (+1) $ M.fromList [(1,2)]' or whatever and expect the proper Data.Map functions to be substituted in. This is a weakness in the GHC API, AFAIK. It is possible that this will be fixed in future versions of Hint or GHC, but I do not expect that to happen for months. * Many limits in System.Posix.Resource are simply completely broken for many users; that is, *no* value can be set using them. I have been unable to figure out the heck why this is the case (I can't reproduce it), and AFAIK no one has filed a bug with the GHC developers, so this probably won't be fixed anytime soon. -- gwern Secure wwics P415 SASP Comirex mailbomb ISADC Sayeret SBI Jatti

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Re: [Haskell-cafe] multi-core programming in Haskell
by Galchin, Vasili 25 Aug '08

25 Aug '08

Thank you Murray. My post was not so clear .... I was referring to "automatic" parellelization vs "manual" parallelization. By "automatic" I mean the programmer doesn't have to indicate where to parallelize ... instead the compiler decides how to parallize! Vasili On Sat, Aug 23, 2008 at 12:58 AM, Murray Gross <mgross21(a)verizon.net> wrote: > > > Vasili: > > Each "par" "sparks" a new thread, which is then queued for execution. At > appropriate points, the threads are distributed to available (free) > processors (cores). The result is that parallelization scales automatically > with the number of available processors. Take a look at the GPH site for > papers that will provide more information on how parallel (and distributed) > Haskell does things. > > Best, > > Murray Gross, > Brooklyn College > > > > > > On Fri, 22 Aug 2008, Galchin, Vasili wrote: > > Hello, >> >> With pure side of the Haskell house, there is hope that the generated >> code could automagically scale as more cores are added yes? It seems that >> it >> is on the stateful monadic side of the house in an appplication that it is >> the programmer responsibility to design the software so that it scales >> across increasing cores? (I am assuming that things like "par" construct >> are >> monadic). On Monday, I am starting a several month project with a company. >> Alledgely some of the code will be written in Python. I would like engage >> the manager in a discussion about multi-core "enabling" the code now when >> we >> design and implement not later as an afterthought. Seems like a gnarly >> subject given current "state-of-the-art" software tools. Ideas?! >> >> Regards, Vasili >> >>

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Why doesn't this work?
by Andrew Coppin 25 Aug '08

25 Aug '08

colour_grid :: (Particle -> IO ()) -> Grid ph -> IO () colour_grid fn g = sequence_ $ runST $ do ps <- grid_coords g mapM (\pix -> do particle <- read_grid g pix return $ fn particle ) ps When I attempt to run this, GHCi just gives me a very cryptic type checker error. I can't figure out what's wrong here. As far as I can tell, this should run...

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(no subject)
by john lask 24 Aug '08

24 Aug '08

Hi has anyone had any success in running a recent version of hs-plugins on a windows platform. I refer to this post to the haskell list in December last year. The current version of hs-plugins dosn't appear to work either. Same problem ... http://www.haskell.org/pipermail/haskell/2007-December/020043.html jvl _________________________________________________________________ Meet singles near you. Try ninemsn dating now! http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Fdating%2Eninemsn%2Ecom%2Eau…

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Type family fun
by Chris Eidhof 24 Aug '08

24 Aug '08

Hey all, I was playing around with type families, and I have a strange problem. Suppose we have an alternative to an Either datatype: > data (:|:) a b = Inl a | Inr b and a class Ix: > class Ix i where > type IxMap i :: * -> * > empty :: IxMap i [Int] Now I want to give an instance for (a :|: b): > instance (Ix l, Ix r) => Ix (l :|: r) where > type IxMap (l :|: r) = BiApp (IxMap l) (IxMap r) > empty = BiApp empty empty BiApp is defined as following: > data BiApp a b c = BiApp (a c) (b c) However, it looks like the recursive calls to empty can't be unified, I get the following error message: Couldn't match expected type `IxMap l' against inferred type `IxMap i' Expected type: IxMap (l :|: r) [Int] Inferred type: BiApp (IxMap i) (IxMap i1) [Int] In the expression: BiApp empty empty In the definition of `empty': empty = BiApp empty empty In the inferred type, there should be IxMap l instead of IxMap i, does anybody know what I'm doing wrong? Thanks, -chris

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ANN: benchpress 0.2.1
by Johan Tibell 24 Aug '08

24 Aug '08

I'm pleased to announce the first public release of benchpress. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/benchpress benchpress is a micro-benchmark library that produces statistics such as min, mean, standard deviation, median, and max execution time. It also computes execution time percentiles. Release bundle: http://hackage.haskell.org/packages/archive/benchpress/0.2.1/benchpress-0.2… Docs: http://hackage.haskell.org/packages/archive/benchpress/0.2.1/doc/html/Test-… Code: git clone git://github.com/tibbe/benchpress.git An example benchmark: > import qualified Data.ByteString as B > import System.IO > import Test.BenchPress > > inpath, outpath :: String > inpath = "/tmp/infile" > outpath = "/tmp/outfile" > > blockSize :: Int > blockSize = 4 * 1024 > > copyUsingByteString :: Handle -> Handle -> IO () > copyUsingByteString inf outf = go > where > go = do > bs <- B.hGet inf blockSize > let numRead = B.length bs > if numRead > 0 > then B.hPut outf bs >> go > else return () > > main :: IO () > main = bench 100 $ do > inf <- openBinaryFile inpath ReadMode > outf <- openBinaryFile outpath WriteMode > copyUsingByteString inf outf > hClose outf > hClose inf And the output, best viewed using a fixed-width font: $ ./example Times (ms) min mean +/-sd median max 232.774 273.611 53.317 266.648 722.332 Percentiles (ms) 50% 266.644 66% 266.826 75% 269.616 80% 295.040 90% 295.360 95% 305.855 98% 350.742 99% 450.855 100% 722.332 Cheers, Johan

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Lines of code metrics
by Dimitry Golubovsky 24 Aug '08

24 Aug '08

Hi, Greg Fitzgerald wrote: >Does anyone know of a good case study comparing a project written in C >versus one written in Haskell? I'm mostly looking for a comparison of lines >of code, but any other metric, such as time to market and code quality >metrics could also be Just curious, has anybody tried to apply Halstead's code metrics (see e. g. http://www.sei.cmu.edu/str/descriptions/halstead_body.html) but there is a 70s' book titled "Elements of Software Science" to Haskell and other functional languages vs. C and other imperative languages? I myself played with these calculations in late 80s trying to estimate code quality of Pascal programs on PDP-11, but that was a pain to count functions' operands properly as they might come from global variables. Application of these formulas to functional languages might be mich cleaner, so has anybody tried? Thanks. -- Dimitry Golubovsky Anywhere on the Web

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