- Haskell-Cafe - Haskell.org

a cabal package with both a library and executable programs
by Manlio Perillo 26 Mar '09

26 Mar '09

Hi. This example is taken from the Cabal documentation: Name: TestPackage ... Library Build-Depends: HUnit Exposed-Modules: A, B, C Executable program1 Main-Is: Main.hs Hs-Source-Dirs: prog1 Other-Modules: A, B Executable program2 Main-Is: Main.hs Hs-Source-Dirs: prog2 Other-Modules: A, C, Utils Here I see a small problem. Why should I explicitly declare modules from the library that are used in the executables? I would like to do, instead ... Executable program1 Main-Is: Main.hs Hs-Source-Dirs: prog1 build-depends: TestPackage Executable program2 Main-Is: Main.hs Hs-Source-Dirs: prog2 build-depends: TestPackag Other-Modules: Utils I tried this, but configuration fails, since Cabal does not find the TestPackage. It is true that it does not yet exists, but we are going to build it! Should I fill a feature request ticket, or this is how it is supposed to work? Thanks Manlio

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Learning Haskell
by Tom.Amundsen 25 Mar '09

25 Mar '09

How long did it take you to become proficient in Haskell? By that, I mean - how long until you were just as comfortable with Haskell as you were with your strongest language at that time? -- View this message in context: http://www.nabble.com/Learning-Haskell-tp22673552p22673552.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: How to increment an Int in Haskell (stack overflow issue)
by John Lato 25 Mar '09

25 Mar '09

> From: Tim Bauer <bauertim(a)eecs.orst.edu> > > I have a program that is currently blowing out the stack, > Stack space overflow: current size 8388608 bytes. > Use `+RTS -Ksize' to increase it. > I am pretty sure I get to the end of the computation that > increments various statistic counters (lazily?) and only > when I go to print them out at the end, do things fail. > In addition to the excellent advice provided by others on this topic, you may want to look at using GHC's heap profiler if you can't track down the source of a memory issue. I've found it helpful in the past. Keep in mind that there are several different modes that may or may not be helpful for a particular problem, so you should try them all to see if you get any useful information. John

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Data Structures with Haskell
by Rohit Agrawalla 25 Mar '09

25 Mar '09

I am a beginner haskell programmer. I am interested in data structures implementation (all from basic ones like stack, queues etc. to advance ones like balanced binary trees, graphs etc.) in haskell. It would be really helpful if someone can point some good references for the same. Regards , Rohit

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ANNOUNCE: WinGhci, a GUI for GHCI on Windows
by Pepe Gallardo 25 Mar '09

25 Mar '09

Hi, I am pleased to announce the first release of WinGhci. WinGhci is a simple GUI for GHCI on Windows. It is closely based on WinHugs, and provides similar functionality. WinGhci project web page: http://code.google.com/p/winghci/<mhtml:{5097F7F7-AA40-4661-A7CF-D5EEC38F084A}mid://00000003/!x-usc:http://co…> Binaries: http://winghci.googlecode.com/files/WinGhci-1.0-bin.zip<mhtml:{5097F7F7-AA40-4661-A7CF-D5EEC38F084A}mid://00000003/!x-usc:http://wi…> Sources: http://winghci.googlecode.com/files/WinGhci-1.0-src.zip<mhtml:{5097F7F7-AA40-4661-A7CF-D5EEC38F084A}mid://00000003/!x-usc:http://wi…> Acknowledgements Much of the code in WinGhci was taken from the Winhugs project. Many thanks to Neil Mitchell for giving us permission to use his code. <mhtml:{5097F7F7-AA40-4661-A7CF-D5EEC38F084A}mid://00000003/!x-usc:http://wi…> Pepe Gallardo

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[ANN] ansi-terminal, ansi-wl-pprint - ANSI terminal support for Haskell
by Max Bolingbroke 25 Mar '09

25 Mar '09

These two packages allow Haskell programs to produce much richer console output by allowing colorisation, emboldening and so on. Both Unix-like (OS X, Linux) and Windows operating systems are supported (via a pure Haskell ANSI emulation layer for Windows). Examples, screenshots, and lots more information about how to get the packages are available at the freshly-minted homepages: http://batterseapower.github.com/ansi-terminal/ http://batterseapower.github.com/ansi-wl-pprint/ These two packages have actually been in stealth release mode on Hackage for some time. However, they seem to be getting some use and I'm not getting any bug reports, so I figure that they /must/ be stable enough to make a proper announcement :-) Cheers, Max (p.s: the GitHub "pages" feature seems to be absolutely ace - highly reccomended! http://pages.github.com/)

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How to increment an Int in Haskell (stack overflow issue)
by Tim Bauer 25 Mar '09

25 Mar '09

I have a program that is currently blowing out the stack, Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. I am pretty sure I get to the end of the computation that increments various statistic counters (lazily?) and only when I go to print them out at the end, do things fail. I have state monad transformer (StateT) that is keeping the counters among other things. The counters are stored in a pair within a larger data structure. > data AState s a = AS { ... > asStats :: (Int,Int) > ... > } to increment them I initially just simply applied either of > incFst, incSnd :: (Int,Int) -> (Int,Int) > incFst (x,y) = (x + 1,y) > incSnd (x,y) = (x, y + 1) to the current pair. I thought this was safe since primitive arithmetic was strict, but when I go to print the counter out (evaluate it), it blows apart. I first decided this was because the addition was somehow not strict and I was getting: (0 + 1 + 1 ...millions of times..., ....) and the evaluation of that first coordinate blew things apart. So I tried was adding a strictness annotation to the arguments. > incFst (!x,y) = (x + 1,y) > incSnd (x,!y) = (x, y + 1) No dice (I also tried using seq manually all over the place to no avail). Just for fun, I tried both of > incFst _ = (0,0) > incSnd _ = (0,0) and > incFst (x,y) = (x,y) > incSnd (x,y) = (x,y) The problem goes away. But maybe an optimization is covering up the crime. So I tried > incFst (x,y) = (y,x) > incSnd (x,y) = (y,x) And indeed this again crashes. Any hints as to what is going on? If it is relevant, here is my code to access the counter within the state monad > countFst :: StateT (AState s a) IO () > countFst = modify $ \as -> as{asStats = incFst (asStats as)} and the monad transformer I am using is > import Control.Monad.State.Strict

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ghci + hopengl
by Rafael Cunha de Almeida 25 Mar '09

25 Mar '09

Hello, I'm writing a program for plotting vectorial functions and maybe something else in the future. My goal is to be able to have the following usage: Prelude> :l Galo.hs Prelude Galo> show3Dvec (\t -> (t, t, 0)) [0.0,0.01 .. 1.0] * shows graph * Prelude Galo> show3Dvec (\t -> (t, t**2, 0)) [0.0,0.01 .. 1.0] * shows new graph * I already done something, the main module can be found here: http://github.com/aflag/galo/blob/0a54a53db0f66384cfc0775f12582931d0fb4205/… The whole project is found here: http://github.com/aflag/galo/tree/master I think mainLoop is somehow responsible to exit the whole thing. I tried to even call that function through forkIO. But didn't work quite well: my terminal started behaving really weird after I closed the window. Could you explain me what is going on and what should I look into for understanding how to solve the issue? []'s Rafael

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Whats the use of "!"
by Harsh Verma 25 Mar '09

25 Mar '09

I have seen ! added in front of many values, is it related to strict evaluation? Please elaborate on it. TIA, gimli _________________________________________________________________ Windows Live Messenger. Multitasking at its finest. http://www.microsoft.com/india/windows/windowslive/messenger.aspx

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central european functional programming school
by Roman Cheplyaka 25 Mar '09

25 Mar '09

Hi, I'm interested in 3rd central european functional programming school[1]. Maybe some haskellers attended previous CEFPs and want to share (or already shared) some experience? Who also is going to attend or participate in this year's CEFP? 1. http://plcportal.inf.elte.hu/en/tfp_cefp_2009/Pages/default.aspx -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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