- Haskell-Cafe - Haskell.org

ANN: newports.hs utility for freebsd
by brad clawsie 29 Jun '07

29 Jun '07

i have written a small haskell program to solve a problem many users of freebsd may have - knowing what ports have been updated after a daily/weekly etc cvsup. this is a trivial bit of coding hardly worth attention, but if it might be of use to you, you can find it here: http://www.b7j0c.org/content/haskell-newports.html standard disclaimers - coded & tested mildly by me, a hobbyist haskeller

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Newbie question: alternative for toInt/fromInt
by peterv 29 Jun '07

29 Jun '07

I'm trying to get the SOE graphics library to compile for Win32 using the latest libraries. I fixed a couple of imports, but in the file GraphicsTypes.hs, the functions toInt/fromInt are used, which are now obsolete: type Dimension = Int toDimension :: Win32.INT -> Dimension fromDimension :: Dimension -> Win32.INT toDimension = toInt fromDimension = fromInt I don't have a clue how to fix this, as I can't find alternatives for toInt/fromInt (except toInteger/fromInteger, but that would convert to heavyweight ints), but I guess it must be really easy? Thanks, Peter

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New New newbie question/help
by Balu Raman 28 Jun '07

28 Jun '07

Hi, Hope someone can help me, just starting out with SOE.My code : module Main where import Graphics.SOE.Gtk spaceClose :: WIndow -> IO() spaceClose w = do k <- getKey w if k == ' ' then closeWindow w else spaceClose w equilateralTri :: Window -> Int -> Int -> Int -> IO() equilateralTri w x y side = drawInWindow w (withColor Red (polygon [(x,y),(a,b),(x,y)])) where b = y + side * sin(pi/3) a = x + side * cos(pi/3) main = runGraphics( do w <- openWindow "Equilateral Triangle" (400,400) equilateralTri w 50 300 200 spaceClose w ) all of the above in file triangle.hs when I do a :l triangle.h in ghci, I get the following error triangle.hs:17:36: No instance for (Floating Int) arising from use of 'pi' at triangle.hs:17:36-37 Probable fix: add an instance declaration for (Floating Int) In the first argument of '(/)', namely 'pi' In the first argument of 'cos', namely '(pi / 3)' In the second argument of '(*)', namely 'cos (pi/3)' Failed, modules loaded: none Can someone help me what's going on to a brand new newbie. All I can figure out is that some type mismatch between float and int . I tried various combinations of lets and wheres and I still get the same complaints. I am just linearly studying SOE Thanks, - br

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Status of MIME Strike Force
by Arie Peterson 28 Jun '07

28 Jun '07

Hi, What is the status of the MIME Strike Force? The goals proposed at <http://www.haskell.org/haskellwiki/Libraries_and_tools/MIMEStrikeForce> promise a very useful library. Has the design been initiated? Kind regards, Arie

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Tools for Haskell and COM
by Lewis-Sandy, Darrell 28 Jun '07

28 Jun '07

Are there any currently maintained tools for interfacing Haskell with COM objects? It appears that both Haskell script and Haskell direct haven't been updated since the turn of the century, and have fallen out of step with recent library changes.

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Re: [Haskell-cafe] HDBC and Sqlite3: SqlValue is restricted to SqlString
by Malte Milatz 28 Jun '07

28 Jun '07

Michael T. Richter: > http://www.sqlite.org/datatype3.html > > Short summary: any data you put into SQLite3 may or may not come out > as text. :D Thanks, Michael. (I'm forwarding this to the list again because there is at least one other person interested.) Well, I've read that page before and I think you're wrong. Sqlite3 is “spontaneously typed”, so to say, but it is still typed. Furthermore the column type gives a hint at how to interpret a value. And what's more, Sqlite3 does not store integers as plain strings anymore, so it seems very unnatural to me for a binding to represent them as strings. Although I do not use Python, I made use of the fact that there are a couple of Python libraries installed on my system, and voilà: >>> print cur.fetchall() [(1, 0, u'a'), (2, 1, u'b')] Here I get my integers as integers and my strings as strings. And, well, Boolean values as numbers, but that's Python's truth philosophy. Anyway, this has convinced me that there is room for improvement in HDBC-Sqlite, unless I have entirely missed something. Regards, Malte

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Yet another implementation of cond
by Jon Cast 28 Jun '07

28 Jun '07

I discovered this trick the other day, and didn't remember seeing it anywhere as a cond implementation: head $ [ e1 | cond1 ] ++ [ e2 | cond2 ] ++ [ e3 | cond3 ] etc. You can even use full pattern guards (more powerful than GHC's) in your conditions! Jonathan Cast http://sourceforge.net/projects/fid-core http://sourceforge.net/projects/fid-emacs

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Cabal Configurations - Beta-Testers Wanted
by Thomas Schilling 28 Jun '07

28 Jun '07

Hello Cafe! Cabal configurations are an often-requested new feature of Haskell's packaging system Cabal. As part of my Google Summer of Code project I implemented it with the feature set of the latest proposal[1]. I would now like people to try it out and give some feedback if it solves their problems, if there are bugs with the current implementation, or if it breaks any install scripts. So, if you have written a package and think your package could profit from Cabal configurations, please adjust your package description and try to build it on as many systems as possible and report any problems (or successes). Following are some instructions to get started. Thanks, / Thomas INSTALLING [Note: The following build instructions are for a recent GHC. If you have another Haskell compiler/interpreter you'll probably have to adjust these steps a bit. Please report any problems you encounter.] You should be able to get Cabal with configurations via: $ darcs get --partial http://code.haskell.org/~nominolo/src/cabal +configs/ Before installing you might want to hide the current cabal package using (tt shouldn't be necessary, though) via $ ghc-pkg hide Cabal or $ sudo ghc-pkg hide Cabal depending on where Cabal is installed. Installing the new Cabal should be as simple as: $ cd cabal+configs $ make install user=y PREF=~/sw This will build Cabal with version 1.1.7, register it in the current user's package database, and install it to the "sw" directory of the current user home directory. Adjust the parameters to your needs. To remove use: $ make remove user=y PREF=~/sw NEW FEATURES The new constructs didn't integrate well with the conventional syntax, so I changed it to a C-style block-style syntax. (This is consistent with Haskell's use of { .. } in do-blocks; adding or replacing this with an indentation-based approach is thinkable and might actually integrate better with the rest of Cabal file syntax. So yell if you want it--but no bike sheds please! ;) The new syntax structures cabal files like this: global properties optional flags descriptions Library { library build properties and conditionals } Executable name { executable build properties and conditionals } For an example, see below. Inside the Library and executable sections you can now use conditionals with the syntax: body: cabal_stanza "\n" body | "if" conditional "{" body "}" [ "else" "{" body "}" ] body | <nothing> conditional: "os(" string ")" | "arch(" string ")" | "flag(" flagname ")" | "True" | "False" | "!" conditional | conditional "||" conditional | conditional "&&" conditional | "(" conditional ")" Note that you cannot test for dependencies directly. The user either specifies certain features she wants by switching flags on or off during the configure step or Cabal picks a suitable flag assignment for you, depending on which dependencies are available. Unless specified otherwise, flag assignments default to True. ATM, the only field specifying dependencies is "build-depends". Options specified inside a conditional are (mostly) added to the values specified outside. E.g. GHC-Options: -Wall if flag(debug) { GHC-Options: -DDEBUG } when built with flag "debug" set to True will be built with GHC-Options: -Wall -DDEBUG For a more detailed description see[1]. The following example .cabal- file should demonstrate the features (it is also available and updated at[2]): Name: Test1 Version: 0.0.1 Cabal-Version: >= 1.1.7 License: BSD3 -- License-File: LICENSE Author: Thomas Schilling <notme(a)nospam.com> Maintainer: Thomas Schilling <notme(a)nospam.com> --Homepage: http://www.example.com/ Synopsis: Test package to test configurations Description: See synopsis. . Really. Category: Useless Flag Debug { Description: Enable debug support Default: False } Flag NoBuild { Description: Inhibit building this package. -- defaults to True } Library { Build-Depends: base Exposed-Modules: Testing.Test1 Extensions: CPP -- flag names are case insensitive if flag(debuG) { CC-Options: "-DDEBUG" GHC-Options: -DDEBUG } if flag(NoBuild) { Build-Depends: nonexistentpackage } } Executable test1e { Main-is: T1.hs Other-modules: Testing.Test1 if flag(debug) { CC-Options: "-DDEBUG" GHC-Options: -DDEBUG } } When configuring it with the usual command line, you now get an additional line, showing which flags were chosen: $ ./Setup.lhs configure configure: Reading installed packages... Configuring Test1-0.0.1... configure: Flags chosen: nobuild=False, debug=False Setup.lhs: Warning: No license-file field. configure: Dependency base-any: using base-2.1.1 [...] Note that, even though the default for the "nobuild" flag was True, the required dependencies weren't present, so it was forced to False. If you want to force flags to certain values you can do so by giving the --flags or -f flag to configure. Listing the (case-insensitive) name forces it to True, putting a "-" in front of the name forces it to False. For example: $ ./Setup.lhs configure -fdebug configure: Reading installed packages... Configuring Test1-0.0.1... configure: Flags chosen: nobuild=False, debug=True Setup.lhs: Warning: No license-file field. [...] or $ ./Setup.lhs configure --flags="-debug nobuild" configure: Reading installed packages... Configuring Test1-0.0.1... Setup.lhs: At least the following dependencies are missing: nonexistentpackage -any $ Note that if you want to change the configuration of a package, you have to ./Setup.lhs clean first, to make sure everything gets recompiled. Good Luck! [1] http://www.mail-archive.com/cabal-devel@haskell.org/msg00282.html [2] http://hackage.haskell.org/trac/hackage/wiki/CabalConfigurations

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Running GranSim on GHC 6.6.1
by Felipe Almeida Lessa 28 Jun '07

28 Jun '07

Hello, everybody! I'd like to know how to compile with GranSim. When compiling anything I get an error about package "concurrent". In fact, it complains even something simple like $ ghc -gransim ghc-6.6.1: unknown package: concurrent This happens with GHC 6.6 from Ubuntu packages and from GHC 6.6.1 compiled from the site tarballs with "./configure --enable-gransim". Is GranSim broken? Or deprecated? Maybe on GHC from Darcs? Or do I have to do something else? I couldn't find anything recent about GranSim (and I've googled quite a lot =). Any pointers are appreciated! Thanks in advance, -- Felipe.

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Reinvention
by Andrew Coppin 27 Jun '07

27 Jun '07

I seem to be forever writing code that looks like this: decode :: String -> (SKI,String) decode (c:cs) = case c of 'S' -> (S,cs) 'K' -> (K,cs) 'I' -> (I,cs) '*' -> let (e0,cs0) = decode cs; (e1,cs1) = decode cs1 in (e0 :@: e1, cs1) In other words, lots and lots of functions with signatures like foo :: [Foo] -> (Bar,[Foo]) that likes to call itself recursively, or that gets called from somewhere else. Is there a Better Way(tm) to do this? It looks like such a common idiom that you'd expect to see "something" in the libraries somewhere. (I remember being puzzled that there was no library function for creating a Cartesian product of two lists. Puzzled until I realised that the monadic nature of lists make it utterly trivial to do this by hand anyway! So it's not always obvious to know what you're looking for...)

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