- Haskell-Cafe - Haskell.org

Darcs-synchronisation tool
by Christophe Poucet 05 Jul '06

05 Jul '06

Hello, I typically back up my darcs repositories on different computers. However I do always use the same structure for the different "forests" of darcs repositories. Lately my laptop charger has died which has led me to constantly use a usbstick to move these repositories. Therefore I have started working on a little tool that will automatically sychronise similarly laid out darcs-forests. At the moment it's very bare-to-the-bones. IT will only darcs pull from the repositories in one forest to the other. I later plan to add options to automatically darcs init when necessary (another thing which I've personally missed from time to time). So, if you find yourself in a similar situation, or you have thoughts, concerns, comments regarding it, feedback is welcome! The source can be found at http://www.notvincenz.com/wiki/uploads/Personal/ApplyDarcs.hs and requires Neil Mitchell's http://www.cs.york.ac.uk/fp/darcs/filepath/System/FilePath.hs renamed as plain FilePath.hs. Cheers, Christophe (vincenz)

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Cyclic Type-synonyms
by Christophe Poucet 05 Jul '06

05 Jul '06

Hello, I use the Indirect Composite pattern a lot, and this means that typically, especially with recursive types (such as an AST), you end up with a lot of data-constructors. I understand that it is not possible to have pure cyclic types (because haskell requires iso-recursive and not equi-recursive types). However I wonder why certain cases can not be allowed. For instance, assume the following somewhat simplified AST: data Exp e = ELet String e e -- let x = a in b | ECond e e e -- If then else construct Now if I wanted to decorate this structure, I would use something like: data AnnotExp a = AE { unAE :: Exp (AnnotExp a), note :: a } However, and this example might be slightly too trivial to motivate it, however it does exemplify what can be done, one might not want to annotate at all and just have a recursive data AST. At this point, one either uses AnnotExp () or creates a new data type. It would be nice if instead one could use cyclic type-declarations, with the knowledge that we're going through a data-constructor and hence the type iso-recursive and not equi-recursive: type AST = Exp AST -- This is iso-recursive as it goes through the data constructors ELet and ECond Sadly this is not possible with the current GHC (I'm using 6..4.2). Is this possible with 6.6? Is there any reason why this is not possible. Feedback regarding this is welcome. A more motivating example can be seen below. Cheers, Christophe ----------------------------- data Exp var ident func exp stm = ELit Lit -- ^ Literals | EVar ident -- ^ Identifiers | EData Const [exp] -- ^ Data Constructors | ECall func -- ^ Function Calls | ELet var stm stm -- ^ Scoping | ECond exp stm stm -- ^ Conditional | ELoop exp stm -- ^ Looping deriving (Eq, Show) data AExp exp annot = AExp { unAExp :: exp, aexpNote :: annot, aexpLoc :: Location } type UnCorExp var annot = Exp var -- ^ Let-binders var -- ^ Named identifiers (Ident, [AExp UnCorExp var annot]) -- ^ Function calls (AExp UnCorExp var annot) -- ^ Expressions (AExp UnCorExp var annot) -- ^ Statements -- Flattened AST: function parameters can only be variables, similar for while- and if- conditions type UnSimExp var annot Exp var -- ^ Let-binders var -- ^ Named identifiers (Ident, [var]) -- ^ Function calls (var) -- ^ Expressions (AExp UnSimExp var annot) -- ^ Statements

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Clever generic ByteString hack?
by John Goerzen 05 Jul '06

05 Jul '06

Hi, In MissingH, I have a bunch of little functions that operate on lists. Some, like uniq (which eliminates duplicate elements in a list), operate on (Eq a => [a]) lists. Others, like strip (which eliminates whitespace at the start and end), operate on Strings only. Most functions of both types would be useful on ByteStrings and lazy ByteStrings. Most of these functions are written in terms of Data.List functions or list primitives that have equivolents in Data.ByteString. So, my question is: is there a clever hack available to me so that I could have 1 version of each function, and have it work on all three different types of input? I'd rather avoid having 3 versions, that are exactly the same except for imports. Thanks, -- John

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Re: [haskell] ANNOUNCE: HNOP 0.1
by mvanier 05 Jul '06

05 Jul '06

[Moving to haskell-cafe] OK, after going through this several times, here's what I've found: 1) The Debian linux build of haskell produces large executables. 2) The generic x86 binary distribution produces smallish executables (383765 bytes; still kind of large; stripped it's 191584 bytes). 3) I removed my entire source distribution, and recompiled from scratch with this build.mk file: SRC_HC_OPTS = -H64m -O2 GhcLibHcOpts = -O2 -fgenerics SplitObjs = YES I did an "autoreconf; configure; make; make install" and then recompiled hnop from scratch. I got large executables (2838528 bytes unstripped, 1540072 stripped). I'm at a loss here. Somehow, the SplitObjs option doesn't seem to be doing the job. Any suggestions would be appreciated. Mike Donald Bruce Stewart wrote: > Hmm. Did you build from scratch? Perhaps the libraries didn't get > rebuilt with split objs ? > > > mvanier: >> I've tried doing a manual build with SplitObjs set to YES, but without >> success; either the compiler was broken or it would still generate large >> executables. So as a sanity check, I installed the debian unstable build. >> But that one also gives me a huge executable: >> >> % ls -l >> total 2720 >> -rw-r--r-- 1 mvanier mvanier 818 Jun 29 20:48 LICENSE >> -rw-r--r-- 1 mvanier mvanier 308 Jun 30 04:59 Main.hi >> -rw-r--r-- 1 mvanier mvanier 80 Jun 29 20:48 Main.hs >> -rw-r--r-- 1 mvanier mvanier 1928 Jun 30 04:59 Main.o >> -rw-r--r-- 1 mvanier mvanier 43 Jun 29 20:48 Makefile >> -rwxr-xr-x 1 mvanier mvanier 2756151 Jun 30 04:59 hnop >> -rw-r--r-- 1 mvanier mvanier 807 Jun 29 23:56 hnop.tar.gz >> >> Am I the only person in the world with this problem? >> >> Also, for some inexplicable reason, debian puts ghci into /usr/X11R6/bin, >> though ghc is in the more sensible /usr/bin/ghc. >> >> TIA, >> >> Mike >> >> Donald Bruce Stewart wrote: >>> mvanier: >>>> Nope, just ghc-6.4.2 that I compiled myself on a Dell x86 laptop (Pentium >>>> M). I didn't use any strange configure options. Is there a special >>>> configure flag for split objects? If not, how is this determined? >>> Ah ha! You need to add -split-objs to the build.mk used by ghc to build >>> its libraries, as described here: >>> http://cvs.haskell.org/cgi-bin/cvsweb.cgi/~checkout~/fptools/ghc/HACKING?co… >>> >>> You want: >>> SplitObjs = YES >>> >>> in mk/build.mk >>> >>> It's not enabled by default, since it doesn't work on every platform. >>> The ghc that is distributed in the debian package system does have split >>> objs on, though. >>> >>> Cheers, >>> Don

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Where is Data.Atom ?
by Brian Hulley 04 Jul '06

04 Jul '06

Hi - I seem to remember from some discussion long ago that there is a Data.Atom module somewhere (hopefully with a BSD licence), but a search on Hoogle turned up no results so maybe I'm mistaken. What I'm looking for is an Atom type and the following operations: fromString :: String -> Atom toString :: Atom -> String instance Eq Atom instance Ord Atom -- this is where things get difficult! It is particularly important that the ordering comparison is extremely fast, preferably independent of the length of the original String, and that it preserves the lexicographic ordering between the original Strings. I can see that an "unsafe" global ref to a Trie of Char with Unique as the "value" of a node would allow me to implement fromString, toString, and instance Eq Atom, but I've got no idea how to implement instance Ord Atom so that the order is independent of the order in which Atoms are created and exactly the same as the lexicographic ordering of the String without being O(n) where n is the min of the lengths of the Atoms being compared. I'm also hoping that Atoms which are no longer in use would manage to magically vanish by themselves. In a Trie implementation, this would mean maintaining an invariant that leaf nodes are always held by a weak link and internal nodes by a strong link. Any ideas (or pointers to a nice downloadable module that already does all this :-) )? Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

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HDF5
by Joel Reymont 04 Jul '06

04 Jul '06

Does anyone have bindings for HDF5 [1]? [1] http://hdf.ncsa.uiuc.edu/whatishdf5.html Thanks, Joel -- http://wagerlabs.com/

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EclipseFP (Haskell IDE) 0.10.0 released
by Thiago Arrais 04 Jul '06

04 Jul '06

EclipseFP 0.10 has been released since last Friday. It is an open-source development environment for Haskell code. EclipseFP integrates GHC with an Haskell-aware code editor and also supports quick file browsing through an outline view, automatic building/compiling and quick one-button code execution. For this new release we have been working on code assistance support, something that has been heavily requested, and a Cabal editor. Downloads and more information are available on the project home page http://eclipsefp.sourceforge.net/ This release requires Eclipse 3.2, as opposed to Eclipse 3.1 that was required on the previous release. You may need to upgrade your Eclipse platform if you plan to use version 0.10. I have taken the liberty to create a wiki page for EclipseFP. You can post your comments and feature requests there, if you'd like. It is located at http://www.haskell.org/haskellwiki/EclipseFP Cheers, Thiago Arrais

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hquickfile first prototype ..
by Marc Weber 04 Jul '06

04 Jul '06

I want your feedback.. The purpose of this program is to get the files/ directories you know faster. Put this into your .bashrc: Of course you have to adjust the executable filename. ============= .bashrc ========================================================== alias F='/usr/bin/hquickfile' Q(){ cd `/usr/bin/hquickfile "$@"` } ============= end .bashrc ====================================================== The source can be found here: http://www.inversoft.de/hquickfile/hquickfile-0.0.tar.gz You need ghc, cabal, parsec and the FilePath library of Neil (Thanks for assisting me!) http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php Things to try: Q /t (equal to cd /tmp) Q /usl (equal to cd /usr/src/linux) .. you should get the idea by reading the help output: ============ hquickfile -h output ============================================= Usage: hquickfile Get the file you want quickly. hquickfile is not a new shell yet but a beginning.. ;) usage: you specify file patterns such as (explanation in bash glob syntax) @vl which will match v.*/l.* (eg var/log on liunux) :abc:def will match .*a.*b.*c.*/d.*e.*f.* =abc will match abc exactly prefix with / to start from root, not current directory windows users have to use /c for c:, /d for d: .. (win not yet tested) to take the first x directories as relative path to start from prepend x to remove the last x directories prepend x- eg cd is /home/marc/hq/ pattern 1-=foo will result in /home/marc/foo pattern 1=foo will result in /home/foo (match file 1 with =1 or @1 append '+' to add not yet existing parts eg you can do mkdir -p `thisapp /@t+a/b/c` to create the /tmp/a/b/c directory append / or : to match directories or files only you can use {blah,foo,...}/ab as you can do in bash which expands to two arguments blah/ab and foo/ab {a,b}{c,d} will expand to ac ad bc cd wheras {a,b}foo[c,d] will expand to afooc bfood {a,b}{c,d}[1,2,3.4] will expand to ac1 ad2 bc3 cd4 you can add glob patterns: ,a/*.txt will ask you wether you want all text files from abc/*.txt or abd/*.txt Because every key you have to type is important you can omit the leading @ so /ea is equal to /@ea would it be useful if small letters would also match capital letters but not the other way round? The Eclipse Plugin GotoFile (written by Max Uermann) does it this way written by Marc Weber Credits to any other haskeller whose tools I've been using (Neil, Pesco, ..) ! especially those on #haskell on freenode who have helped me a lot by listening -h, --help print this help ========== end hquickfile -h ================================================ I think there are still some bugs.. Marc Weber

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JRegex on "large" input sizes
by David House 03 Jul '06

03 Jul '06

Hi all. I need a decent regex library and JRegex seems the perfect choice: simple API, yet well-featured, as well as PCRE support. I want to use it on a simple project which involves input files a little larger than typical -- between 100KB and 500KB -- but still small enough so as to not present a problem. However, and I'm fairly sure JRegex is at fault here, my program segfaults on an input of ~230KB. Has anyone used JRegex successfully in this way before? If so, what tactics did you use? Thanks in advance. -- -David House, dmhouse(a)gmail.com

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Input/Output file
by Sara Kenedy 03 Jul '06

03 Jul '06

Hi all, I have a module Test.hs: module Test where import IO readMsgFile = do putStr "Input file: " ifile <- getLine putStr "Output file: " ofile <- getLine s <- readFile ifile writeFile ofile (test s) --test function test :: String -> String test s |s == "true" = "True" |s == "false" = "False" |otherwise = [] Then, I run *Test> readMsgFile Input file: test1.txt Output file: result1.txt The content of test1.txt is string "true". So I expect the result in "result1.txt" is "True" But, open file "result1.txt", it displays empty. I do not know why it does not return correct answer. If you don't mind, please share with me. Thanks a lot. S.

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Re[2]: Debugging with GHCi.
by Bulat Ziganshin 03 Jul '06

03 Jul '06

Hello Pepe, Monday, July 3, 2006, 2:15:59 PM, you wrote: > As you may know, this project was accepted for Google SoC and work started a > few weeks ago. There are now some observable results that can be tested, and > I have set up a wiki page at: > http://haskell.org/haskellwiki/Ghci/Debugger > As we are now approaching the less clear parts of the project your > impressions and ideas (either extense designs or small pointers) are very > welcome. The designs for dynamic breakpoints and call traces are open issues > yet. i'm very pleased with this year's selection of SoC projects and debugging is among the things i'm highly demanded. I personally interested in debugging imperative C-like code, with abilities to set breakpoints, watch (and change?) variable values, see "call stack" (i think that closures stack should serve this need), see local variables at each "call stack" level, evaluate expression and perform IO actions it's especially important for me to be able to use debugger inside some IDE that will allow to set breakpoints and ask variables' values directly inside the source code I'd written. i can recall the following haskell IDEs: HIDE, EclipseFP, Haskell mode for Emacs, Visual Haskell, WinGhci. I think their authors will say better what kind of interface with debugger they prefer imho, just console I/O interface should be enough for most IDEs, as long as debugger's output can be non-ambiguously parsed. Gdb often used to debug C++ programs inside IDEs in this way, i think that cloning it's interface should make it easier to integrate GhcDebugger support into IDEs i also vote for simplest implementation of dynamic breakpoints - the tight integration with IDEs, i.e. _features_, is more important than efficiency (if i correctly understood that this may change only an efficiency) I also will appreciate ability to view call traces - it's the thing that i really need sometimes, especially when debugging unexpected exceptions like "head: empty list". It will be especially great to see all variables' values at each execution moment. I don't have a great ideas about representation of this trace. One obvious idea would be to save some binary file and write special viewer for it, another possible idea is to produce (gigantic) html with trace represented as tree with usual '+' marks to expand each node. ps: you will not get much answers - first, because it's a summer and most Haskellers prefer at this time to set up breakpoints on bodies of their girlfriends ;) second - because this maillist don't have many readers. i suggest you to dup your question into main Haskell list and i cc'ed my answer to haskell-cafe in advance. but nevertheless your project is really important to make Haskell more usable for everyday work and Haskellers returned from their vacations will be glad to see that their debugging tasks becomes much easier. please also write exhaustive documentation at the end of your work so that ghci debugger will not become "black hole" feature -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Re[4]: [Haskell-cafe] EclipseFP (Haskell IDE) 0.10.0 released
by Bulat Ziganshin 03 Jul '06

03 Jul '06

Hello Piotr, Monday, July 3, 2006, 10:27:22 AM, you wrote: >> - syntax highlighting, including highlighting of bracket's pair >> - fast access to help about identifier >> - auto-indenting with user-tuned style > Personally I consider these 3 essential, so I'd vote for them to be > implemented in first place (in order as above). I think will test that > code completion today - out of sheer curiosity ;) i answer in cafe so that Thiago can see you preferences :) for me, compilation & errors navigation, syntax highlighting and code navigation is minimal required features set. help is actually replaced by code navigation - function's definition in Haskell typically contains appropriate help text (which is eventually extracted by Haddock and placed into html file). The only advantage of using pure html help is to omit all the unneeded information (implementation details and so on) and see beautiful formatted text with hyperlinks smart indentation is not easy for Haskell, i think. I don't even sure that myself has some strict indenting rules. moreover, with many edits of source files this again loses it's meaning i'm also curious about code completion - never worked with good one (after the MultiEdit's support for C language constructs :) ) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 34, Issue 45
by Jeremy O'Donoghue 03 Jul '06

03 Jul '06

Hi Jason, Just as a short follow-up on the question of installers: On 27/06/06, Jason Dagit <dagit(a)codersbase.com> wrote: > On 6/27/06, Jeremy O'Donoghue <jeremy.odonoghue(a)gmail.com> wrote: > > > > My applications are mainly for internal use at my workplace, and come > > with Windows installers (I use Inno setup with wxHaskell - never > > managed to make it work with GTK2, so these applications were > > delivered as zip files which just had to be unzipped in a certain > > place). > > Do you have any advice about using Inno with haskell? Have you tried > wix at all? > http://sourceforge.net/projects/wix/ I haven't looked at Wix. Inno is particularly straightforward as it has a 'wizard' interface (the script wizard). The basic steps (for wxHaskell) are: On screen 1: add application name, version, publisher and website (if applicable) On screen 2: add application install base directory and directory name. Decide if user can change these or not. On screen 3: add main application executable. Add any other files/directories used (In my case, I typically have only the main .exe file, wxmsw24.dll, wxc-msw2.4.2-0.9.4.dll and, possibly, a bitmaps directory and/or help files). On screen 4: Decide where in the start menu you will put the application. On screen 5: Any application documentation: license, pre-install readme, post-install readme. On screen 6: Define any language support details. On screen 7: Define setup compiler output directory, output filename, any icon to be used and (optionally) a password. That's it. The wizard generally produces all I need for a simple installer. > Maybe you have a developer blog I could read? I don't. I fear that I would start full of good intentions, write a few posts and then find that I had no time... I'll try to share what I know via the wiki as Simon suggested (will be putting this installer stuff, suitably edited, in the wiki shortly). Regards Jeremy

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System.FilePath, Request for comments
by Neil Mitchell 02 Jul '06

02 Jul '06

Hi, I have written a System.FilePath module in part based on the one in Yhc, and in part based on the one in Cabal (thanks to Lemmih). The aim is to try and get this module into the base package, as FilePath's are something many programs use, but its all too easy to hack up a little function that gets it right most of the time on most platforms, and there lies a source of bugs. This module is Posix (Linux) and Windows capable - just import System.FilePath and it will pick the right one. Of course, if you demand Windows paths on all OS's, then System.FilePath.Windows will give you that (same with Posix). Written in Haskell 98 + Heirarchical Modules. Haddock: http://www-users.cs.york.ac.uk/~ndm/projects/filepath/System-FilePath.html Darcs: darcs get http://www.cs.york.ac.uk/fp/darcs/filepath Source: http://www.cs.york.ac.uk/fp/darcs/filepath/System/FilePath.hs Homepage: http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php Tests: http://www.cs.york.ac.uk/fp/darcs/filepath/Tests.hs If you go to the haddock page there are a few little examples at the top of the file. If anyone could make any comments on the interface, the semantics of the operations (look at the Tests file if you don't want to go prodding the code), missing features etc. that would be very handy. The interface is not yet stable as a warning to those who choose to use it (although I hope its close - that depends on your comments!) Thanks Neil PS. Thanks to Marc Webber for code contributions, shapr for suggestions and a few others.

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Simple List Question
by Jenny678 02 Jul '06

02 Jul '06

Hello Little Problem, hope that somebody can help me I have a list >main [(1,2,3),(4,5,6),(3,4,5)] and i want all Elements at the 1. Pos. in new List: >[1,4,3] Thanks for help -- View this message in context: http://www.nabble.com/Simple-List-Question-tf1880239.html#a5139831 Sent from the Haskell - Haskell-Cafe forum at Nabble.com.

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Not in scope: type constructor or class
by Joel Reymont 02 Jul '06

02 Jul '06

Folks, I'm getting this error: ./HOC/StdArgumentTypes.hs:1:0: Not in scope: type constructor or class `HOC.Arguments:ObjCArgument' But if you look through the output below you will see that HOC.Arguments is being loaded by ghc. I assume that's what the skipping of HOC.Arguments means. The Arguments module starts like this so I believe it's exporting everything: module HOC.Arguments where import HOC.Base import HOC.FFICallInterface import Foreign.Storable import Foreign.ForeignPtr import Foreign.Ptr import System.IO.Unsafe(unsafePerformIO) import Language.Haskell.TH import Language.Haskell.TH.Syntax class (Storable b, FFITypeable b) => ObjCArgument a b | a -> b where withExportedArgument :: a -> (b -> IO c) -> IO c exportArgument :: a -> IO b importArgument :: b -> IO a objCTypeString :: a -> String StdArgumentTypes.hs starts like this so you see that it's importing HOC.Arguments module HOC.StdArgumentTypes where import HOC.Base import HOC.Invocation import HOC.Arguments import HOC.FFICallInterface import Control.Exception ( bracket ) import Foreign import Foreign.C.Types import Foreign.C.String -- Objective C -- ID: already defined instance FFITypeable SEL where makeFFIType _ = makeFFIType (undefined :: Ptr ()) $(declareStorableObjCArgument [t| SEL |] ":") instance ObjCArgument Bool CInt where exportArgument False = return 0 exportArgument True = return 1 importArgument 0 = return False importArgument _ = return True objCTypeString _ = "c" The line 1 in the error below makes me guess that it could be a Template Haskell issue. Any pointers? Thanks, Joel --- ghc --make HOC.hs -odir build/objects -hidir build/ imports -fglasgow-exts -package-name HOC ../ HOC_cbits/HOC_cbits.o -I../HOC_cbits -I../ libffi-src/build/include -framework Foundation -fth Chasing modules from: HOC.hs Skipping HOC.SelectorNameMangling ( ./HOC/SelectorNameMangling.hs, build/objects/HOC/SelectorNameMangling.o ) Skipping HOC.Base ( ./HOC/Base.hs, build/objects/HOC/Base.o ) Skipping HOC.FFICallInterface ( ./HOC/FFICallInterface.hs, build/ objects/HOC/FFICallInterface.o ) Skipping HOC.Arguments ( ./HOC/Arguments.hs, build/objects/HOC/ Arguments.o )Skipping HOC.Utilities ( ./HOC/Utilities.hs, build/ objects/HOC/Utilities.o )Skipping HOC.Invocation ( ./HOC/ Invocation.hs, build/objects/HOC/Invocation.o ) Skipping HOC.MsgSend ( ./HOC/MsgSend.hs, build/objects/HOC/ MsgSend.o ) Compiling HOC.StdArgumentTypes ( ./HOC/StdArgumentTypes.hs, build/ objects/HOC/StdArgumentTypes.o ) Loading package base-1.0 ... linking ... done. Loading object (static) ../HOC_cbits/HOC_cbits.o ... done Loading object (framework) Foundation ... done final link ... done Loading package haskell98-1.0 ... linking ... done. Loading package template-haskell-1.0 ... linking ... done. ./HOC/StdArgumentTypes.hs:1:0: Not in scope: type constructor or class `HOC.Arguments:ObjCArgument' ./HOC/StdArgumentTypes.hs:1:0: `exportArgument' is not a (visible) method of class `Arguments:ObjCArgument' ./HOC/StdArgumentTypes.hs:1:0: `importArgument' is not a (visible) method of class `Arguments:ObjCArgument' ./HOC/StdArgumentTypes.hs:1:0: `objCTypeString' is not a (visible) method of class `Arguments:ObjCArgument' -- http://wagerlabs.com/

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ghc does not want to link statically
by Joel Reymont 01 Jul '06

01 Jul '06

Folks, I'm trying to compile the Haskell Objective-C Binding (HOC) and it needs /usr/lib/libSystemStubs.a to find the missing _fprintf$LDBLStub symbol. I tried the following in the make file FOUNDATION_LIBS=-static -lSystemStubs -l dynamic -framework Foundation but ghc still tries to link libSystemStubs.a dynamically. How do I fix this? ghc --make HOC.hs \ -odir build/objects -hidir build/imports \ -fglasgow-exts -package-name HOC \ ../HOC_cbits/HOC_cbits.o \ -I../HOC_cbits \ -I../libffi-src/build/include \ \ -static -lSystemStubs -dynamic -framework Foundation \ ... Loading package base-1.0 ... linking ... done. Loading object (static) ../HOC_cbits/HOC_cbits.o ... done Loading object (dynamic) SystemStubs ... failed. Dynamic linker error message was: dlopen(libSystemStubs.dylib, 10): image not found Whilst trying to load: (dynamic) SystemStubs Directories to search are: /opt/local/lib ghc-6.4.2: user specified .o/.so/.DLL could not be loaded. make[1]: *** [ghcmake.build-stamp] Error 1 Thanks, Joel -- http://wagerlabs.com/

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Re: ANNOUNCE: HNOP 0.1
by Simon Marlow 01 Jul '06

01 Jul '06

My congratulations to the development team; this is an important contribution to the community. You might want to use {-# OPTIONS_GHC #-} rather than {-# OPTIONS #-}, unless compatibility with older versions of GHC is a goal. Still, the pragma only turns on warnings, so it's harmless. Ashley Yakeley wrote: > One interesting line of development would be to spin off the core > functionality into a separate library, to provide no-op services to > other Haskell applications. I'm thinking something like this: > > noop :: IO () -- generalise to other Monads? Only IO makes sense really, since by definition every non-IO expression does nothing, so the only interesting way to do nothing is in the IO monad. I imagine this interface would be relatively stable. I'm not sure at this stage where in the module hierarchy we should place it, though. Cheers, Simon

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lifting between two StateT monads
by Alexander Vodomerov 01 Jul '06

01 Jul '06

Hello! I've just started learning Haskell and have a simple question regarding monads. Please, don't blame me if it is too obvious (any RTFM links are welcome). Suppose, we have two data types, X and Y. X represent local state, Y -- global one. In some sense, X is contained in Y. For example, Y maybe (X, Z) or [X] or Map Int X. Let's take that (as it is in my case) Y = Map Int X I have function that make some transormation of local state (X) and having some other side effects. f :: StateT X m a where m is another monad, something like WriterT Log IO. Now I want to convert it into function transorming global state, more specifically it's n-th part. So, I want to combine n :: Int and f into g :: StateT Y m a where (Y ! n) is transormed via f, and other parts of Y are not touched. How can this be done? I've looked through StateT documentation and tutorial, but had not found any function from StateT X to StateT Y where Y is not the same as X. With best regards, Alexander.

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Re: ANNOUNCE: HNOP 0.1
by Ashley Yakeley 01 Jul '06

01 Jul '06

> Now we just need the Godot version, in which nothing happens twice. You may have to wait for that. -- Ashley Yakeley Seattle WA

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Re: [Haskell] Re: ANNOUNCE: HNOP 0.1
by Neil Mitchell 01 Jul '06

01 Jul '06

> > It would be interesting to compile it with John Meacham's Jhc, which > > claims to leave very little overhead in its executables. I know the > > current Jhc has a limit on total program size, but the current HNOP at > > least may slip under the wire (and I don't make any use of arrays, so it > > shouldn't be too slow). > > ; jhc -v Main.hs > 6Kb yhc Main.hs ls Main.hbc 113 bytes Thanks Neil

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Re: [Haskell] Re: ANNOUNCE: HNOP 0.1
by Robert Dockins 30 Jun '06

30 Jun '06

[moved to cafe] On Jun 30, 2006, at 4:01 AM, Ashley Yakeley wrote: > In article > <252C89C12FCAD84BA018CAD5268682FD0190C955(a)GBLONXMB02.corp.amvescap.net > >, > "Bayley, Alistair" <Alistair_Bayley(a)invescoperpetual.co.uk> wrote: > >> Cool, that's awesome. But I don't see any Haddock docs? Or a Cabal >> Setup.hs? Would it be much trouble to add them? > > Bear in mind HNOP compiles just to an executable file, so it doesn't > really have a Haskell API. > > One interesting line of development would be to spin off the core > functionality into a separate library, to provide no-op services to > other Haskell applications. I'm sorry; I know this is a serious discussion (either that or everyone involved in this discussion has a more subtle sense of humor than I), but this sentence made me laugh out loud... :-) "no-op services"? That's just great! > I'm thinking something like this: > > noop :: IO () -- generalise to other Monads? > > This would actually not be too hard to write, given my existing work, > and then of course the executable would simply be a thin wrapper. > > -- > Ashley Yakeley > Seattle WA Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG

2 1

Haskell I/O inside: down the rabbit's hole
by Bulat Ziganshin 30 Jun '06

30 Jun '06

Hello Haskell, I'm just wrote exhaustive introduction to Haskell I/O titled HASKELL I/O INSIDE: DOWN THE RABBIT'S HOLE Can you please help me (and Haskell community) by proof-reading this text? Even if you will correct paragraph or two, it will advance the work further. Also feel free to add more explanations, correct me and ask (here) about new topics you need to be explained. The page is http://haskell.org/haskellwiki/IO_inside -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

2 2

Re[2]: [Haskell-cafe] Haskell I/O inside: down the rabbit's hole
by Bulat Ziganshin 30 Jun '06

30 Jun '06

Hello Donald, Friday, June 30, 2006, 1:20:03 PM, you wrote: >> http://haskell.org/haskellwiki/IO_inside > Perhaps mention > http://research.microsoft.com/~simonpj/Papers/marktoberdorf > "Tackling the awkward squad: monadic input/output, concurrency, > exceptions, and foreign-language calls in Haskell" > for people wanting to go further into the area? of course. feel free to add anything you think is useful. like 'Arrays' page, it is collective work, and like this page it can go much further from it's initial state. a have added a section, but it needs further editing -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

1 0

Re: Speed of ByteString.Lazy
by Chad Scherrer 30 Jun '06

30 Jun '06

Then I should be thanking Duncan as well (thanks!). I had seen the array fusion idea before in the NDP work, but I hadn't thought of applying to this area. I wonder where else the concept might apply? Is there a typeclass to be built? -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx Cheers! Duncan Coutts and I have put in many long hours in improving the bytestring code over the last 3 months, in particularly the Lazy bytestring library, and array fusion on bytestrings. You can see here, http://www/~dons/images/commits/fps-commits.png<http://www/%7Edons/images/commits/fps-commits.png>, some 200 patches a month :} Its gratifying to find out that people really use the code :) -- Don -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

1 0

A question about stack overflow
by Huazhi (Hank) Gong 29 Jun '06

29 Jun '06

Hi, all I'm just a newbie for Haskell and functional programming world. The idea I currently read is quite different and interesting. I have one general question about the recursively looping style. For example: myMax [ ] = error "empty list" myMax [x] = x myMax [x:xs] = if x>= (myMax xs) then x else (myMax xs) I just list out this kind of very simple program. However, if the list size if a big number such as 10000000, the Winhug will report that the stack is overflow. Does it mean that the functional programming is lacking of scalability? I do know that we can manually change the stack size for it. But that's not a good solution according to my opinion. Yours, Hank

6 6

how to write an haskell binding
by minh thu 28 Jun '06

28 Jun '06

hi, hopefully (well, i liked the discussions) this message will not spawn so much messages :) i'd like to know if there exist some general guidelines/information about writing an haskell (or is it *a* haskell ?) binding for a c or a c++ library. i worry about : * implementation tools : use tools like c2hs or others, or do that bare hands * haskell idioms/usage : make good use of monads, type classes and other haskell related things * for c++, is it better to first write a c api for the c++ code before writing the binding * maybe advice about the c api knowing there will be haskell binding * any thing i forgot thanks a lot, thu

8 14

Deducing Show for GADTs
by Joel Björnson 28 Jun '06

28 Jun '06

Hi. I came a cross the following phenomena which, at least to me, occurs kind of awkward. The code below : data MyData a where DC1 :: (Show a ) => a -> MyData a instance Show (MyData a) where show (DC1 a ) = show a yields the ghci error : 'Could not deduce (Show a) from the context (Show (MyData a))' Adding a Show restriction for the instantiation as in instance Show a => Show (MyData a ) where show (DC1 a ) = show a makes the type checker happy. However, this means that all parametrised values over MyData must have a Show type which isn't necessarily what one wants. I would also like to point out that adding a 'wrapper type' as in data Wrap a = Wrap a data MyData a where DC1 :: (Show a ) => a -> MyData (Wrap a) instance Show (MyData a ) where show (DC1 a ) = show a works fine. Even though 'Wrap' does not derive Show. So, if anyone can give me some hints about the reason for this, I will appreciate it :) Thanks /Joel

4 3

Cabal and linking with static libs (.a files)
by Ketil Malde 28 Jun '06

28 Jun '06

(Reposted to café - my -libraries mail seems to have gotten lost along the way) Hi, I'm building an interface to a C library, which comes in the form of two .a files. I can't seem to get Cabal to link statically with these, so that the resulting package (libHSfoo-v.v.a) is self contained. I've tried fiddling with Cabal's ld-options and extra-libraries, but so far with no success - loading my package either results in GHC looking for (and failing to find) .so files, or "unknown symbol". Help? -k PS: did --user stop working (with GHC 20060607)? I'm adding --user to both 'configure' and 'install', but Cabal still wants to put things in /usr/local. -- If I haven't seen further, it is by standing in the footprints of giants

2 6

Are FunPtr's stable? (was: how to write an haskell binding)
by Brian Hulley 28 Jun '06

28 Jun '06

Bulat Ziganshin wrote: > Hello Brian, > > Tuesday, June 27, 2006, 2:43:15 AM, you wrote: > >> achieve a goal. One other thing to bear in mind is that foreign >> calls are extremely slow, so for example it is much faster to use the >> Foreign.Marshal.Array and Foreign.C.String functions to allocate and >> populate a temporary array with the contents of a list, and send the >> pointer to this array to C with one foreign call, than to send each >> element of the list with multiple foreign calls (eg to paste only >> 19K of text from the Windows clipboard to my app took over 1 >> minute!!! > > he-he-he :) just add "unsafe" specifier: Thanks Bulat! It turns out nearly every foreign function I'm using doesn't make callbacks into Haskell so can be marked "unsafe" so your solution has saved me an enormous amount of refactoring... :-) On a related note, as I was reading the FFI specification again, I can't find any mention of whether or not FunPtr's are stable with respect to garbage collection. I'm assuming they are but am I correct? Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

3 4

closures with side effects
by tpledger＠ihug.co.nz 28 Jun '06

28 Jun '06

dkarapet wrote: > I have been trying to understand closures > in haskell and how they relate > to side effects. I have been looking > around but all I find are trivial > examples with no side effects. Please let > me know if you know of any examples. The side effects occur in the context that causes the closure to be entered. Here's a nigh-trivial example. myClosure :: IO () myClosure = putStrLn "Hello, world." main = myClosure >> myClosure When myClosure is defined, the side effect doesn't occur yet. We just have a *definition* of an IO action that hasn't yet been bound into the program's sequence of actions. When main binds myClosure into the program's sequence of actions (twice), the side effect occurs (twice). Depending on the implementation of putStrLn, it may be faster the second time because the same closure has been entered before. HTH, Tom

1 0

Re: [Haskell] Google SoC: Software Transactional Memory for Parrot
by John Meacham 28 Jun '06

28 Jun '06

On Tue, Jun 27, 2006 at 08:29:21AM -0700, Jared Updike wrote: > >Am I the only one whose first instinct upon reading this is "EW!"? > > You are not the only one, judging from my own experience. I made my > own sort of algebraic datatypes / abstract datatypes in C# by using > Enums and Objects and runtime casts. It works, but the code itself is > hairy. I guess the good news is that once I built the ADT the---in my > case, ugly---implementation is hidden. When I first started using Haskell Sather was my language of choice. As I learned Haskell and all it's cool features I kept wanting to "backport" them to Sather... Algebraic data types was one of the things I proposed to the sather community, a wacky idea for an OO language of sathers heritage. but it was not long after then that I realized I should just be using Haskell to begin with and redirected my efforts here. :) John -- John Meacham - ⑆repetae.net⑆john⑈

1 0

Re: Haskell-Cafe Digest, Vol 34, Issue 45
by Jason Dagit 27 Jun '06

27 Jun '06

On 6/27/06, Jeremy O'Donoghue <jeremy.odonoghue(a)gmail.com> wrote: > Hi Jason. > > My $0.02 > > On 27/06/06, haskell-cafe-request(a)haskell.org > <haskell-cafe-request(a)haskell.org> wrote: > > ---------- Forwarded message ---------- > > From: "Jason Dagit" <dagit(a)eecs.oregonstate.edu> > > > Requirements: > > Okay, so now that you know why I'm here, let me give you an idea of > > what my *ideal* GUI library would be for this project (roughly in > > order of importance): > > 1) Doesn't require the end user to install anything (no dependencies) > > 2) Looks and feels like windows > > 3) Robust (or mature) > > 4) A pleasure to program (boo @ swing) > > 5) ?? > > > > I don't really know the landscape, but this is my (uneducated) idea of > > my options: > > A) wxWidgets > > B) gtk2hs > > C) win32 api > > D) write the gui in C or C++ and use the FFI to invoke it > > E) write the gui in scala or java and use FFI + JNI to invoke it > > F) ?? you tell me > > > > I think (although I have yet to verify) that (A) satisfies #1-4, but > > (B) doesn't satisfy #1. Is this true? I tried to install wxHaskell > > but it turned out to be a real pain. I'm using visual haskell so that > > I have COM support (I need the version of H/Direct that ships with > > VisualHaskell and VisuallHaskell only ships with ghc 6.5) and that > > means I have to compile the less mainstream haskell libraries myself. > > I have yet to successfully install wxHaskell on my dev machine at > > work. > > I've developed a couple of projects with wxHaskell, along with a > couple using the lablGtk2 library for Ocaml - in fact, the whole > clunkiness and lack of Windows and (especially) Mac native feel of GTK > on non-Linux platforms is a large part of what brought me to Haskell > :-) > > My applications are mainly for internal use at my workplace, and come > with Windows installers (I use Inno setup with wxHaskell - never > managed to make it work with GTK2, so these applications were > delivered as zip files which just had to be unzipped in a certain > place). Do you have any advice about using Inno with haskell? Have you tried wix at all? http://sourceforge.net/projects/wix/ Maybe you have a developer blog I could read? > To distribute wxHaskell applications you need only two DLLs and an > executable. All can be in the same directory. I think this covers 1) Yes, I would say that's almost ideal. (Ideally the user wouldn't even have to install my progam it would 'just work' ;) > Look and feel is Windows native. As an added bonus (for me, at least) > it also looks native on Mac and Linux. That's 2) Yes, I've used wxPython in the past very successfully. It's fast, easy to use, tends to look right. (in my narrow opinion) > wxHaskell is fairly robust, but you need to be aware that it does not > have complete coverage of the wxWindows library. I have found layout > behaviour to be incomprehensible at times (although I found this to be > somewhat true of the native wxWindows sizers on which layout is > built). Some of the more exotic widgets (Scintilla, wxGrid) are either > not wrapped, or the wrapping is incomplete. I have not succeeded, in > the general case, in getting sash wiondows to work as I would like > them to (it's possible for some limiting cases, but that is not enough > for my needs) Hmm...Yes I've fought extensively with the layout managers for Java that come with the Net Beans IDE. I think using a layout manager is a great idea, but then I'll spend several hours fighting with getting just one screen to layout correctly and never want to use layout managers again. Perhaps I'm just dense, but the Matisse gui builder in Net Beans is really frustrating for me. > My impression, sadly, is that little development now goes on on > wxHaskell. The last compiled binaries available from the website are > over a year old now and, as you've already discovered, it's really > quite difficult to get wxHaskell to compile on Windows. For what it's > worth, I gave up on 2.6.x and reverted to 2.4.2, which compiled > cleanly for me. I took a hint here and downloaded 2.4.2, followed the instructions to the letter and got things almost working. It seems that I had spaces in my paths. VisualHaskell installed to: C:\Program Files\Visual Haskell When I came to the step of compiling wxHaskell I needed to run configure with these options: ./configure --libdir=C:/Progra~1/Visual~1 The two important things here are: 1) You must use the forward slash and 2) you cannot use spaces. After it installed I started getting panics from 'ghc -package wx': http://www.haskell.org/pipermail/glasgow-haskell-bugs/2005-October/005632.h… And I found a solution here: http://www.haskell.org/pipermail/glasgow-haskell-bugs/2005-October/005639.h… Next I found that I needed to add C:\Program Files\Visual Haskell to my path so that the wxHaskell dlls could be located by windows. Now I'm at the point where I can compile and run wxHaskell programs (yay!). > > Because of the appearance that it's withering on the vine, I would be > reluctant to recommend wxHaskell. However, despite the gripes above, I > think it's a superb piece of work. I have managed to produce some very > high performance applications with it - users assumed that I had > written in hand-optimized C (FastPackedStrings also had a big hand in > the performance). If the project were better documented, I really > believe that there's a chance that the project would take off. As an > example, I easily have the knowledge of C/C++ needed to contribute, > and the Haskell is getting there, but the (lack of) documentation > makes it hard for the end user at times - let alone the wannabe > developer. When I used wxPython I was often referencing the C++ docs and I didn't mind as I'm reasonably fluent in C++. So (hopefully) this will not slow me down when using wxHaskell. > wxHaskell programming is something of a mix of Haskell idioms (layout, > in particular) and C style imperative programming (in IO monad). In > some respects the UI code looks quite similar to wxPython, but at > least you get Haskell goodness for everything else. This is a big > plus. This is something I'm looking forward to. A little bit of not-as-pretty Haskell with lots of typical Haskell to support it. I think it will make my project fun to work on as well as giving me certain bonuses in the software engineering department (go referential transparency!). [snipped testimonials about gtk2hs] Thanks for the info about gtk2hs. I feel like GTK is great and I would gladly use it on an open source project but I think given my target audience and my requirements it's not right for this project. > > I can't really comment on your other potential solutions. Hopefully I won't need them now :) Thanks, this was very helpful, Jason

1 0

Re: Haskell-Cafe Digest, Vol 34, Issue 45
by Jeremy O'Donoghue 27 Jun '06

27 Jun '06

Hi Jason. My $0.02 On 27/06/06, haskell-cafe-request(a)haskell.org <haskell-cafe-request(a)haskell.org> wrote: > ---------- Forwarded message ---------- > From: "Jason Dagit" <dagit(a)eecs.oregonstate.edu> > Requirements: > Okay, so now that you know why I'm here, let me give you an idea of > what my *ideal* GUI library would be for this project (roughly in > order of importance): > 1) Doesn't require the end user to install anything (no dependencies) > 2) Looks and feels like windows > 3) Robust (or mature) > 4) A pleasure to program (boo @ swing) > 5) ?? > > I don't really know the landscape, but this is my (uneducated) idea of > my options: > A) wxWidgets > B) gtk2hs > C) win32 api > D) write the gui in C or C++ and use the FFI to invoke it > E) write the gui in scala or java and use FFI + JNI to invoke it > F) ?? you tell me > > I think (although I have yet to verify) that (A) satisfies #1-4, but > (B) doesn't satisfy #1. Is this true? I tried to install wxHaskell > but it turned out to be a real pain. I'm using visual haskell so that > I have COM support (I need the version of H/Direct that ships with > VisualHaskell and VisuallHaskell only ships with ghc 6.5) and that > means I have to compile the less mainstream haskell libraries myself. > I have yet to successfully install wxHaskell on my dev machine at > work. I've developed a couple of projects with wxHaskell, along with a couple using the lablGtk2 library for Ocaml - in fact, the whole clunkiness and lack of Windows and (especially) Mac native feel of GTK on non-Linux platforms is a large part of what brought me to Haskell :-) My applications are mainly for internal use at my workplace, and come with Windows installers (I use Inno setup with wxHaskell - never managed to make it work with GTK2, so these applications were delivered as zip files which just had to be unzipped in a certain place). To distribute wxHaskell applications you need only two DLLs and an executable. All can be in the same directory. I think this covers 1) Look and feel is Windows native. As an added bonus (for me, at least) it also looks native on Mac and Linux. That's 2) wxHaskell is fairly robust, but you need to be aware that it does not have complete coverage of the wxWindows library. I have found layout behaviour to be incomprehensible at times (although I found this to be somewhat true of the native wxWindows sizers on which layout is built). Some of the more exotic widgets (Scintilla, wxGrid) are either not wrapped, or the wrapping is incomplete. I have not succeeded, in the general case, in getting sash wiondows to work as I would like them to (it's possible for some limiting cases, but that is not enough for my needs) My impression, sadly, is that little development now goes on on wxHaskell. The last compiled binaries available from the website are over a year old now and, as you've already discovered, it's really quite difficult to get wxHaskell to compile on Windows. For what it's worth, I gave up on 2.6.x and reverted to 2.4.2, which compiled cleanly for me. Because of the appearance that it's withering on the vine, I would be reluctant to recommend wxHaskell. However, despite the gripes above, I think it's a superb piece of work. I have managed to produce some very high performance applications with it - users assumed that I had written in hand-optimized C (FastPackedStrings also had a big hand in the performance). If the project were better documented, I really believe that there's a chance that the project would take off. As an example, I easily have the knowledge of C/C++ needed to contribute, and the Haskell is getting there, but the (lack of) documentation makes it hard for the end user at times - let alone the wannabe developer. In short, I'm not sure about 3). wxHaskell programming is something of a mix of Haskell idioms (layout, in particular) and C style imperative programming (in IO monad). In some respects the UI code looks quite similar to wxPython, but at least you get Haskell goodness for everything else. This is a big plus. Back in the day when I was using the Ocaml GTK2 binding, the following observations were true. I suspect they may be true of GTK2Hs (as they are mainly observations on GTK2 on Windows per se), but I am not certain. Installation of GTK2 on Windows is nothing short of revolting. It's a completely manual set of 'work out which DLL or library to download from where and install it in a suitable directory. Building from source is worse. I never managed to work out a small, sane set of DLLs which could just be packaged with the executable I was delivering. It may be possible, but I didn't manage it. That's a fail on 1), I suspect. Look and feel is adequate on Windows, for the most part. However, the file dialog, in particular, caused my users (mainly engineers, so pretty switched on, on the whole) no end of confusion, and was a major driver to my dropping Ocaml for this type of work. That's a failure on 2), at least for me. However, in its defence, GTK2 is stable and capable on Windows. I also have the impression that GTK2Hs is much more actively developed than wxHaskell, and this may be a good reason to choose it if what you are producing is a prototype which will not have wide distribution. I think you'd have to give GTK2Hs a good rating for 3). I can't really comment on your other potential solutions. Regards Jeremy

1 0

RE: [Haskell-cafe] A question about stack overflow
by voigt.16734551＠bloglines.com 27 Jun '06

27 Jun '06

--- Huazhi (Hank) Gong" <hankgong(a)nm.gist.ac.kr wrote: > Thank you very much for introducing tail recursion. > It's my first time to hear this. :) > However, I'm wondering whether every loop structure from C like language can > be translated to this kind of tail recursion? Yes, as discovered by John McCarthy almost 50 years ago in "Recursive functions of symbolic expressions and their computation by machine. Communications of the ACM, 3:184-195, 1960". Ciao, Janis Voigtlaender.

1 0

[GHC/Base.A_o] Error 1
by gaa＠cin.ufpe.br 27 Jun '06

27 Jun '06

Anyone can help me? I did some changes in the .mk and makefile files in order to integrate it with the Haskell.NET code generator but when I try to compile the following error appears: ../../ghc/compiler/ghc-inplace -H32m -O -W -fno-warn-unused-matches > -fwarn-unuse > d-imports -fglasgow-exts -cpp -Iinclude -#include HsBase.h -Icbits/regex > -funbox > -strict-fields -package-name base -O -dcore-lint -W > -fno-warn-unused-matches -fw > arn-unused-imports -fglasgow-exts -keep-msil-files -fvia-il -hisuf A_hi > -hcsuf > A_hc -osuf A_o -fvia-il -keep-msil-file -c GHC/Base.lhs -o GHC/Base.A_o > -ohi > GHC/Base.A_hi > GHC/Base.lhs:296: parse error on input `.' > make[3]: *** [GHC/Base.A_o] Error 1 > make[2]: *** [all] Error 1 > make[1]: *** [all] Error 1 > make[1]: Leaving directory `/cygdrive/c/Guilherme/ghc-6.2.2/libraries' > make: *** [build] Error 1 > > > > Thanks, Guilherme A. Avelino

2 1

Win32 GUI bindings
by Jason Dagit 27 Jun '06

27 Jun '06

I'm looking for recommendations (testimonials?) for GUI libraries for haskell (ghc 6.5) on the win32 platform that meet my requirements below. But first, I try to motivate my question. Bit of background: I work at a smallish software company and I've been given a project where I'm supposed to create a prototype which will later be scraped and a new version will be written that is part of our main product. The prototype will only ever run on windows and it will be distributed to customers for a year or two before it is assimilated. I've used python a bit to prototype the prototype and figure out some of the basics. I'll need a small GUI (maybe one or two dialogs), an XML library, a few small parsers and COM support. I was going to put Haskell back on the shelf and use either python or scala for this project because of the COM requirement but just today I made a major breakthrough with H/Direct and it looks like Haskell is back in the running. So far I plan to use HaXml, parsec and H/Direct but I still need some way to create a gui. This project is fairly representative of all the work we do at my company so I feel if I find a good solution this time it's probably what I'll focus on using in the future. That's part of the reason I'm trying out python, Haskell and scala. (Perhaps the real reason is just that I like playing with languages ;). Requirements: Okay, so now that you know why I'm here, let me give you an idea of what my *ideal* GUI library would be for this project (roughly in order of importance): 1) Doesn't require the end user to install anything (no dependencies) 2) Looks and feels like windows 3) Robust (or mature) 4) A pleasure to program (boo @ swing) 5) ?? I don't really know the landscape, but this is my (uneducated) idea of my options: A) wxWidgets B) gtk2hs C) win32 api D) write the gui in C or C++ and use the FFI to invoke it E) write the gui in scala or java and use FFI + JNI to invoke it F) ?? you tell me I think (although I have yet to verify) that (A) satisfies #1-4, but (B) doesn't satisfy #1. Is this true? I tried to install wxHaskell but it turned out to be a real pain. I'm using visual haskell so that I have COM support (I need the version of H/Direct that ships with VisualHaskell and VisuallHaskell only ships with ghc 6.5) and that means I have to compile the less mainstream haskell libraries myself. I have yet to successfully install wxHaskell on my dev machine at work. I think that (C) is going to violate #4 and maybe #3 depending on how much code I need to write to get the bare windows api to do what I want. Plus I doubt this makes sense for a long term solution. I think (D) makes less sense than (C) and I doubt it's a nice way to do things, I'm probably better off with (C). As for (E), why don't I just do the whole thing in scala if I'm requiring the GUI to be in scala? Advice? Thanks, Jason

3 3

Simple matrix
by Atila Romero 26 Jun '06

26 Jun '06

I made a very simple matrix module that implements matrix sum and multiplication. It does not require any especific type since it uses Num [[a]]. So instead of typing something like Matrix [[1,0],[0,2]] * Matrix [[1,2],[3,4]] you can just type [[1,0],[0,2]]*[[1,2],[3,4]] It needs -fglasgow-exts Atila module SimpleMatrix where instance Num a => Num [[a]] where fromInteger x = [[fromInteger x]] abs x = map (map abs) x (+) [ ] y = y (+) x [ ] = x (+) x y = zipWith (zipWith (+)) x y (*) x y = map (matrixXvector x) y where -- matrixXvector :: Num a => [[a]] -> [a] -> [[a]] matrixXvector m v = foldl vectorsum [] $ zipWith vectorXnumber m v -- vectorXnumber :: Num a => [a] -> a -> [a] vectorXnumber v n = map (n*) v -- vectorsum :: [a] -> [a] -> [a] vectorsum [] y = y vectorsum x [] = x vectorsum x y = zipWith (+) x y _______________________________________________________ Novidade no Yahoo! Mail: receba alertas de novas mensagens no seu celular. Registre seu aparelho agora! http://br.mobile.yahoo.com/mailalertas/

8 17

closures with side effects
by dkarapet 26 Jun '06

26 Jun '06

I have been trying to understand closures in haskell and how they relate to side effects. I have been looking around but all I find are trivial examples with no side effects. Please let me know if you know of any examples.

3 2

Scoped data declarations
by Christophe Poucet 26 Jun '06

26 Jun '06

Dear, Yesterday, while discussing with Cale and SamB on I suddenly came up with the crazy idea of scoped data declarations. After some brief discussion to check the validity, I finally came to the conclusion that they should be feasible. In addition, I don't think that they would require a high amount of changes in current compilers. Basically if you have something like: module Main where foo = let data Foo = Foo deriving Show in Foo\ main :: IO () main = print foo One can see this as having an extra hidden module that defines Foo but that does not export it. The only change that is then required is that while compiling Foo, the hidden-ness of Foo must be removed. For instance, if one were to load this into, say, ghci (this is fictive of course): # ghci Main.hs > :t foo foo :: Codeloc2.Foo There were initially some objections to this, because it is no longer feasible to actually write the type of the function foo. But if one looks at current GHC, this objection is already there: module A(foo) where data Foo = Foo deriving Show foo = Foo module Main where import A main = print foo As Excedrin then pointed out, importing this Main into ghci, gives foo :: Foo.Foo And this notation can not be written in Main either, because Foo is hidden in A. Therefore, I would like to note that scoped data declarations are just like hidden data-declarations with two extra requirements: 1) Generate source-location-based submodule names 2) Add an extra import rule for those hidden modules in the subexpressions of where the data-declaration is being originally defined. Comments are welcome, of course :) Cheers! Christophe (vincenz)

3 3

Re: [Haskell-cafe] Re: Functional progr., infinity, and the Universe
by voigt.16734551＠bloglines.com 26 Jun '06

26 Jun '06

--- paul.hudak(a)yale.edu wrote: Jerzy Karczmarczuk wrote: > > OK, I think that this subject matured enough to rest in peace... > > I would have to agree with that, although... Since the subject is not going to rest, why not also jump in? > Well, each partial list is finite. I think quite a few people would agree that a finite list is one ending in []. So 1:_|_ is a partial list, but not a finite one. 1:[] is a finite list. > But the limit of a chain IS the maximal element of the set of all > elements comprising the chain, since the LUB, in the case of a chain, is > unique, and thus we don't have to worry about choosing the "least" > element (i.e. it reduces to the upper bound, or maximal element). That doesn't quite make sense, IMHO. The chain _|_, 1:_|_, 1:1:_|_, 1:1:1:_|_, ... has the limit (or upper bound) "ones", but "ones" does not appear in the chain. An upper bound of a set may not appear in the set. But the maximal element of a set by definition ("element of") necessarily is in the set. So you cannot use the two notions interchangably. BTW, if the limit of a chain would always appear in the chain (by virtue of being the maximal element of the set of all elements comprising the chain), then every chain would be stationary eventually. That would quite simplify denotational semantics, wouldn't it? > So I'd say that Brian has at least come close to discovering God :-) And come to the conclusion, in a later mail, that both: A. "the list [0,1,2,3,4,5,..] is longer than [1,2,3,4,5,..]" and B. "ie [0,1,2,3,4,..] is the same length as [1,2,3,4,5,..]" I think not. Obviously not. I know that this conclusion was qualified by "assuming that they all grow at the same rate", which of course has no counterpart in the denotational semantics setting discussed above. So it's not a wrong statement, just one that cannot really be formulated. Well, anyway, didn't want to be nitpicking. But I think it's important that if we want to think about Haskell's semantics denotationally (which in itself is somewhat problematic), we should at least be careful not to blur concepts. And asserting that the limit of a chain is always an element of that chain is a dangerous oversimplification that does not work out. Ciao, Janis Voigtlaender.

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parsec, how to feed single tokens?
by Marc Weber 25 Jun '06

25 Jun '06

Hi. I want to write a haskellquickfind app to get a list of files using human readable hash values (eg the first character of directory/filenames) Eg hquickfind vtl should print /var/tmp/local My implementation should look like this: Every folder/file is token and I want to run a parser. to consume /var Then I want to run it with all subdirs in var where it should fail on anything but t.* ... My Problem : I can't access runP directly to feed the parser with one token and get the result (failure, need more tokens).. Have I missed a function or isn't parsec meant to be used this way? Would you recommend writing your own small parser for this? Another question: Can you use another SourcePos state than SourcePos? Marc

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Haskell developer is needed
by pvainuk＠aol.com 25 Jun '06

25 Jun '06

An enthusiastic Haskell Developer with good C++ skills is needed to assist with the rollout of a new system. This is a high profile project and the successful candidate will work in a very strong business oriented team where they will gain experience in wide variety of products and systems. Essential skills include: Haskell language, C++, office technology, Windows environment. Some finance knowledge is desired, but not essential. The ideal candidate with in depth understanding of computer science basics must be passionate about Haskell. You will need a 1st class computer science degree or demonstrate sound work experience. A successful candidate must be prepared to work under the pressure in the very dynamic environment extended hours. This is an excellent opportunity for a talented developer to join a well established company with global presence and to work on the most cutting edge technologies and to really progress your career. Location: HQ, London, UK Please send your CV to pvainuk(a)aol.com

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ReadP and MonadFix
by Gracjan Polak 24 Jun '06

24 Jun '06

Hi all, A question for hot summer day: Text.ParserCombinators.ReadP.ReadP is an instance of Monad. Could it be an instance of MonadFix too? I'm not that sharp in Haskell to write it myself, but it seems I could make use of such a beast. :) Anybody willing to share? This will also present the advantage of Lazy over Eager Parser Combinators, mentioned in some other thread. -- Gracjan

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Binary IO
by jeff lasslett 24 Jun '06

24 Jun '06

Greetings, I am considering writing -in Haskell of course - a small program to translate binary files to human readable text. The trouble is that I can find no easily digestible tutorial style info on how to do binary IO in Haskell. I have read about some of the libraries that people have created to do binary IO, but the documentation wasn't sufficient to get me started (perhaps because I'm a bit dense, and also relatively new to Haskell). What I would like is to see a short example showing some code that reads from a binary file. I would also like to know what the most widely used library for doing binary IO in Haskell is. I would greatly appreciate it if someone could post a small example or two illustrating how to do binary IO in Haskell using the most widely used binary IO lib (if there is such a thing). Failing that, I would appreciate a link to some Haskell code that does binary IO that I could study. Lastly, if there is a good tutorial on doing binary IO in Haskell then I would appreciate a link to that as well. Thanks in advance, Jeff Lasslett

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newbie - IO issues (of course)
by Geoffrey King 24 Jun '06

24 Jun '06

I have been work my way through "Haskell The Craft of Functional Programming", all was fine until IO (chapter 18). That is causing me bafflement. I am trying to write a totally trivial program that reads a series of integers from the console until it gets a zero, then returns the series of integers as a list. I am down to randomly editing my code, never a good sign. Any clues would be appreciated, My code so far, which clear doesn't work, is: getInt :: IO Int getInt = do putStr "Enter number (zero to quit)" line <- getLine return (read line :: Int) anIntList :: [Int] anIntList = do let n = getInt if n == 0 then return [] else return (n : anIntList) ps: even a simple version that returns an Int i can't get to work. anInt :: Int anInt = do n <- getInt return n

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Lambda abstraction analogous to imperative pseudo-code?
by Clifford Beshers 23 Jun '06

23 Jun '06

The Wikipedia article on lambda abstractions (http://en.wikipedia.org/wiki/Lambda_abstraction) has a statement that does not resonate with me: A lambda abstraction is to a functional programming <http://en.wikipedia.org/wiki/Functional_programming> language such as Scheme <http://en.wikipedia.org/wiki/Scheme_programming_language> what pseudo-code <http://en.wikipedia.org/wiki/Pseudo-code> is to an imperative programming <http://en.wikipedia.org/wiki/Imperative_programming> language. Does anyone else find this to be a peculiar statement? If you think it is accurate, could you provide an alternate explanation and/or example to the one in the article?

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Functional programming for processing of large raster images
by oleg＠pobox.com 23 Jun '06

23 Jun '06

Recently Vo Minh Thu wondered if Haskell (or, I generalize, functional programming) can be of much use for computer graphics programming. I'd like to point out a project that experimentally shown that functional programming is of great help for processing of large raster images (24-bit PPM files). The paper describing the system has been accepted for `Science of Computer Programming' and is in press: Combining Partial Evaluation and Staged Interpretation in the Implementation of Domain-Specific Languages Christoph A. Herrmann, Tobias Langhammer The code for the system is available online http://infosun.fmi.uni-passau.de/cl/metaprog/imagefilter2-2005-10-30.tgz The previous [slightly obsolete] version of the paper, presented at the MetaOCaml'04 workshop, is available online http://www.fmi.uni-passau.de/forschung/mip-berichte/MIP-0410.html The paper includes a few pictures and the table with benchmark, so we can observe the benefits. Now, with offshoring and native MetaOCaml fully implemented, we can gain bigger benefits. In this project, functional programming does what it is probably best suited: to develop a `compiler' -- a compiler from a filter specification to quite efficient code. The code is specialized to all available static information. To be precise, the authors implement an interpreter -- which is then specialized to the source program and so interpretative overhead is removed and the code is optimized. Staging an interpreter automatically gives a compiler. Futamura projections are not only the fascinating, but useful, too.

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Re: [Haskell-cafe] Re: Functional progr., infinity, and the Universe
by voigt.16734551＠bloglines.com 23 Jun '06

23 Jun '06

--- paul.hudak(a)yale.edu wrote: voigt.16734551(a)bloglines.com wrote: > 1:_|_ is certainly finite. In what sense is it not? I see that point. I have been using "finite" as, by convention, equal to "total and finite". And so have others. As always with convention, one can argue. I won't, of course. > Sorry, see my reply to Bill Wood. Yes, saw that later. > distinguishes what are called "interesting" elements from other elements > (if I recall the terminology correctly). Interesting ;-) Ciao, Janis.

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sortBy2 for List library
by Serge D. Mechveliani 23 Jun '06

23 Jun '06

Consider the following suggestions for the standard Haskell library `List'. ------------------------------------------------------------------------ import List (intersprerse, insertBy) compose :: [a -> a] -> a -> a -- just appropriate name compose = foldr (.) id insertBy2 :: (a -> b) -> Comparison b -> a -> [a] -> [a] insertBy2 f cp a xs = map fst $ insertBy (\ p p' -> cp (snd p) (snd p')) (a, f a) [(x, f x) | x <- xs] Similar are mergeBy2, sortBy2. type ComparisonValue = LT | GT | Eq deriving ... -- better name than `Ordering' type Comparison a = a -> a -> ComparisonValue ------------------------------------------------------------------------ Motivation example for `compose': myShowsList :: Show a => [a] -> String -> String myShowsList xs = compose $ intersperse (", "++) $ map shows xs myShowsList ("; "++) [1,2,3] --> "1; 2; 3" Motivation example for insertBy2: Consider the program insertBy (\ n m -> compare (f n) (f m)) 100 [0 .. 1000], where f :: Integer -> Integer is expensive to compute. We see that the program insertBy2 f compare 100 [1 .. 1000] spends 2 times less of `f' invocations, and looks natural. ----------------- Serge Mechveliani mechvel(a)botik.ru

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