July 2003 - Haskell - Haskell.org

Function composition and currying
by Dr Mark H Phillips 25 Jul '03

25 Jul '03

Hi, Hopefully this is a simple question. I am wanting to know good ways of using ".", the function composition operator, when dealing with currying functions. Suppose I have the following functions defined: f :: Int -> Int f x = x*x g :: Int -> Int -> Int g a b = a + b If I wish to add 1 and 2 together and then square them I can do: f (g 1 2) = 9 but what if I wish to use function composition in the process? I can't do (f.g) 1 2 because the 2 doesn't get passed in till too late. I could do (f.(g 1)) 2 or even (f.(uncurry g)) (1,2) But what I really want is a function with signature Int -> Int -> Int. The answer is probably: (curry (f.(uncurry g))) 1 2 but this seems awfully messy just to do f (g 1 2). And what if g were a function with three curried arguments? Then uncurry and curry wouldn't apply. What then? Is there a better way? Thanks, Mark. -- Dr Mark H Phillips Research Analyst (Mathematician) AUSTRICS - smarter scheduling solutions - www.austrics.com Level 2, 50 Pirie Street, Adelaide SA 5000, Australia Phone +61 8 8226 9850 Fax +61 8 8231 4821 Email mark(a)austrics.com.au

17 28

Announce: wxhaskell: MacOSX installer
by Arthur Baars 24 Jul '03

24 Jul '03

I have created an "out-of-the-box" MacOS X installer for wxHaskell. Simply double-click on the package. The installer can be downloaded from: http://home.deds.nl/~dediav/WxHaskell.dmg This link is only valid for a couple of weeks. After Daan returns from holidays he'll probably put it on the wxHaskell pages. Note the package only works with ghc 6.0 or higher! The installer does the following: 1) copy wxWindows and wxHaskell libraries to /usr/local/wxhaskell 2) register the wx and wxh packages with ghc-pkg To uninstall, type in a Terminal: 1) rm /usr/local/wxhaskell 2) ghc-pkg -r wxh 3) ghc-pkg -r wx The package also contains the wxHaskell documentation and samples. Copy them to your disk. To test the installation: Open a terminal in the samples/wx directory, and write: 1) ghc --make -package wx Camels.hs -o camels 2) /usr/local/wxhaskell/bin/macosx-app --program=camels 3) ./camels The macosx-app script is located at /usr/local/wxhaskell/bin; you may want to add this directory to your PATH. Have fun :-)) Arthur >From: "Daan Leijen" <daanleijen(a)xs4all.nl> >Date: din jul 22, 2003 19:47:27 Europe/Amsterdam >To: <haskell(a)haskell.org>, <gui(a)haskell.org>, ><wxhaskell-users(a)lists.sourceforge.net> >Subject: [wxhaskell-users] Announce: wxhaskell: macOSX binaries and bugfix. >Reply-To: <daanleijen(a)xs4all.nl> > >Two announcements regarding wxHaskell: ><http://wxhaskell.sourceforge.net> > >1) I have created a binary release for MacOS X. Installation details can > be found on the download page. > >2) I have fixed a small bug in the configuration script for Linux. The > source release has been updated. (and I promise I won't do that again > as I go tomorrow on a holiday for two weeks :-) > >All the best, > Daan. _________________________________________________________________ Tired of spam? Get advanced junk mail protection with MSN 8. http://join.msn.com/?page=features/junkmail

1 0

ANNOUNCE: Haskell/Java VM Bridge 0.2.1 Release
by Ashley Yakeley 23 Jul '03

23 Jul '03

Release 0.2.1 of Haskell/Java VM Bridge is now available in source-code form. 0.2.1 is a minimal update to work with GHC 6.0. If you are using GHC 5.04, you should use the 0.2 release instead. Haskell/Java VM Bridge allows Haskell programs access to the Java Virtual Machine. It comes in two parts: the 'Native' part, that abstracts away differences in the various Java VMs, and the 'Haskell' part that provides a Haskell API. The Native part is not Haskell-specific, and could potentially be used by other languages wishing to access the Java VM. Features include: * Calling of Java methods, access to fields, array-handling; * Integration of garbage collectors; * Reconciliation of exception models; * Reconciliation of thread models, including 'synchronized' monitor support and the ability to fork Haskell actions as Java threads; * Strong typing for Java classes and method argument lists (as tuples), and use of Haskell lists as arrays; * Creation of Java classes 'on the fly' (using DefineClass and the Java Class File Format) that can have Haskell callback methods; * Lifted monads which do all the necessary JNI class and method/field ID preloading and 'JNIEnv'-pointer variable handling for you -- these can be automatically generated via a tool (MakeJVMModule); * Layered design includes lower-level IO-based interface; * Automatic generation of modules for Java API classes; * All relevant imports, flags and libraries etc. handled by a single GHC package 'javavm'; * No 'unsafe' Haskell calls or pure function FFI anywhere; * Easy to port to new Java VMs. This release should be 'beta' quality, but has undergone little testing. You will need: * An x86 machine running some form of Unix, or a Mac OS X machine; * GHC 6.0 or later; * A Java VM. It's been tested only with Sun's JVM, but should (may?) work with a number of others. Haddock documentation is currently blocked on a bug in Haddock ("implicit parameters"). Should that be fixed, you will be able to build API documentaion by doing "make doc". Some simple examples have been included such as a program that shows a Java Frame containing an instance of a Haskell-defined subclass of Canvas that has a Haskell 'paint' method that draws an oval. You should be able to figure out most of it from that. Haskell/JVM Bridge and source code is licensed under the GNU Lesser GPL. <http://sourceforge.net/projects/jvm-bridge/> Future plans: * port to Cygwin * use hierarchical module structure * separate out pure (non-FFI) Haskell into a separate package * better typing for the IO-based layer -- Ashley Yakeley, Seattle WA Almost empty page: <http://semantic.org/>

1 0

Announce: wxHaskell, a portable GUI library.
by Daan Leijen 23 Jul '03

23 Jul '03

Announcement: wxHaskell 0.1 --------------------------- <http://wxhaskell.sourceforge.net> wxHaskell is a new portable GUI library for Haskell. The goal of the project is to provide an industrial strength portable GUI library, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore build on top of wxWindows -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with native look-and-feel, and it has a very active community (ranked among the top 25 most active projects on sourceforge). Since most of the interface is automatically generated from the wxEiffel binding, the current release of wxHaskell already supports about 75% of the wxWindows functionality -- about 2500 methods in 500 classes with 1200 constant definitions. wxHaskell has been build with GHC 6.0 on Windows, MacOS X and Unix systems with GTK. A binary distribution is available for Windows (and we are working on a binary release for MacOS X). And even if you don't intend to write GUI's yourself, it will be fun to check out the screenshots at <http://wxhaskell.sourceforge.net>. All the best, Daan Leijen.

3 3

varying function by typeclass
by Abraham Egnor 23 Jul '03

23 Jul '03

I have a function that takes, among other things, a (wrapped) generic type, i.e. "forall a. a". My function can possible produce an error message; is there any way to set up the function so that if the type is an instance of Show include the value along with the error message? I can't think of any, and this is honestly the first time I've been directly frustrated by Haskell's typesystem, so it's bugging me more than it might otherwise. Any suggestions? Abe

1 0

HToolkit 1.0 released
by Krasimir Angelov 22 Jul '03

22 Jul '03

+-------------------------------------------------------+ | ANNOUNCEMENT: HToolkit 1.0 released | +-------------------------------------------------------+ | author: Krasimir Angelov | | www : http://htoolkit.sourceforge.net | | forum : mailto://htoolkit-users@lists.sourceforge.net | +-------------------------------------------------------+ The HToolkit is a package primary intended for development and designing of platform independent graphical user interface. The package gives you an abstract API for many platforms while for each platform are used only libraries which are native for the platform. This release supports only Windows and Linux platforms, but the chosen model allows support for other platforms. Under Windows the package use only native Win32 API and under Linux are used GTK/GNOME libraries. The difference between HToolkit and most of other libraries is that the latter uses only controls and dialog elements which are native under target plaform. The advantage of this is that the application looks like more native. Similar model is chosen from wxWindows for C++ and SWT for Java. The disadvantage of this libraries is that they are written in high level languages and this makes difficult to use them from other languages. The main part of HToolkit is written in C and the used model simplifies FFI interface between the HToolkit core and high level languages (most languages proposes only FFI to C). The current release gives only interface to Haskell. There is plan to build GUI libraries based on HToolkit core for C#, SmallTalk and Python. HToolkit for Haskell -------------------- HToolkit �� Haskell is divided in two libraries: GIO and Port. The Port library is a low level interface and it is not intended to be used for development. Port includes modules written in C and FFI for them written in Haskell. GIO is a high level API intended for application development. The HToolkit is divided in high and low level in order to allow development of experimental high level interfaces without sacrifice of low level API. For the time beings HToolkit gives all features proposed from ObjectIO with exception of ToolBar and CustomControl. Many of ObjectIO features are extened, but there are also many new features which does't exists in ObjectIO. Relatively all controls supported from wxHaskell are supported from HToolkit. Still missing controls like Panel, Gauge and Notebook but they are planned for the next release of HToolkit. Currently the HToolkit is the only package for Haskell which allows to create, load, edit and save images at runtime. Another interesting feature is that the toolkit allows to display icons in menu items. The feature is native under GTK/GNOME but is hard to implement under Windows. NOTE: The ToolBar support is included in the package but still doesn't work. This is because under Windows it still requires a bit of development while under GTK/GNOME the package uses the new API for GtkToolbar which will be part of the next GTK release. Krasimir Angelov __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com

1 0

Announce: wxhaskell: macOSX binaries and bugfix.
by Daan Leijen 22 Jul '03

22 Jul '03

Two announcements regarding wxHaskell: <http://wxhaskell.sourceforge.net> 1) I have created a binary release for MacOS X. Installation details can be found on the download page. 2) I have fixed a small bug in the configuration script for Linux. The source release has been updated. (and I promise I won't do that again as I go tomorrow on a holiday for two weeks :-) All the best, Daan.

1 0

Superclass Defaults
by Ashley Yakeley 21 Jul '03

21 Jul '03

This seems to be a frequently requested feature of Haskell: the ability to declare default members in a superclass for a particular class. Here's an example: class Functor f where fmap :: (a -> b) -> f a -> f b class (Functor f) => Monad f where ... The idea is that it should be possible to declare a type an instance of both Monad and Functor without having to provide a definition for 'fmap'. Instead, a default would be used: fmap ab fa = fa >>= (return . ab) Well I don't doubt this would be a very useful extension to the Haskell language: indeed it would eliminate code in all my Haskell projects. But before we can propose this, we have to work out what the syntax would look like. Here are some properties I think such a mechanism should have: 1. It should be possible to declare types as instances of Monad and Functor with a different definition of fmap overriding the default. 2. It should be possible to declare another subclass of Functor that also has a default for fmap. 3. The members of any existing class should be subclass-defaultable in another module; i.e., no special syntax should be involved in the class declaration of the superclass. 4. It should be possible to distinguish between different appearances of the same class in the superclass context. For instance: class C a where c :: Int -> a class (C a,C b,C (a -> b)) => D a b where ... Any ideas? -- Ashley Yakeley, Seattle WA

2 1

HScheme Status
by Ashley Yakeley 20 Jul '03

20 Jul '03

HScheme, my Scheme interpreter, is mostly done. I've put up the latest build as a CGI program, together with lists of features and issues standing before release. See: <http://hscheme.sourceforge.net/> Curiously (or not), parsing is by far the biggest time hit. I hope to do a bit more profiling to see if I can find out just why. -- Ashley Yakeley, Seattle WA

1 0

RE: referring to deeply embedded definitions
by Hal Daume 18 Jul '03

18 Jul '03

Please ignore my stupid question :) -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: Hal Daume > Sent: Friday, July 18, 2003 10:23 AM > To: haskell(a)haskell.org > Subject: referring to deeply embedded definitions > > > Suppose I have: > > > module M1 where > > import M2 > > foo = 'a' > > and > > module M2 where > > import M3 > > and > > > module M3 where > > foo = True > > Now, inside M1, I want to write something like: > > > bar = if M2.foo then M1.foo else 'b' > > or > > > bar = if M3.foo then M1.foo else 'b' > > but neither of these is valid. Is there any way to get at > the definition from M3? > > - Hal > > -- > Hal Daume III | hdaume(a)isi.edu > "Arrest this man, he talks in maths." | www.isi.edu/~hdaume >

1 0