July 2006 - Haskell-Cafe

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 01 Jul '06

01 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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