If you're already used to C++ Qt and PyQt, qtHaskell should be relatively straightforward (though probably with a few gotchas).
You could download qtHaskell and look at the examples to get an idea for the feel of it. If you're already used to Qt they should look familiar.

Subclassing _is_ done a little weird:

First you declare a dummy datatype:

data MyQPushButton = MyQPushButton

And then you use the qSubClass function:

myQPushButton :: String -> IO (QPushButton MyQPushButton)
myQPushButton s = qSubClass $ qPushButton1 s

The type signature here is necessary. It's the only thing that forces the new (QPushButton a) to be a QPushButton MyQPushButton.

Then you can use your subclassed buttons like so:

main :: IO ()
main = do
    app <- qApplication
    dialog <- qDialog
    button1 <- myQPushButton "Click for Stuff"
    qObject_connectSlot1 button1 "clicked()" button1 "click()" $ on_pbutton_clicked dialog
    mainLayout <- qVBoxLayout
    qLayout_addWidget mainLayout button1
    qWidget_setLayout dialog mainLayout
    qWidget_setWindowTitle dialog "Stuff Test"
    ok <- qDialog_exec dialog
    return()

on_pbutton_clicked :: QDialog () -> QPushButton MyQPushButton -> IO ()
on_pbutton_clicked _dlg _this  = do
    mb <- qMessageBox1 _dlg
    qMessageBox_setText mb $ "Stuff"
    qWidget_show mb
    return ()

Hmmm, though it doesn't look like you can currently overload methods of your parent class, usually you don't need too though as you can just tie into a signal (so you still can do things like paint). Though I'm kinda suprised I didn't notice this before, I'll have to email the guy and see if this is actually an issue.

Also, qtHaskell doesn't fully support all the Qt widgets (though it covers most of them) but there is a new version coming out soon that should be more complete.

Overall qtHaskell has served my perposes well.

There is also a good listing of GUI toolkits for Haskell at http://www.haskell.org/haskellwiki/Applications_and_libraries/GUI_libraries

- Job

On Tue, Sep 1, 2009 at 1:49 AM, Michael Mossey <mpm@alumni.caltech.edu> wrote:
Thanks for the info. Interesting. I'm already familiar with C++ Qt and also PyQt. I am also a fan of Qt.

However, as a beginner to Haskell, I want to be sure I don't get myself into trouble. I hope that qtHaskell is straightforward.

Qt depends on deriving user classes. How is this handled in qtHaskell?

Thanks,

-Mike


Job Vranish wrote:
I recommend qtHaskell.
I am a big fan of Qt in general. It has good documentation and extensive examples, is very well designed, and has a good license. I'd even say the C++ version is good choice for beginners (certainly easier to understand/use than say GTK).
The qtHaskell bindings are also pretty good. The documentation and examples are not as extensive, but you can usually use the C++ documentation to fill in the gaps.
Being already familiar with C++ Qt, using qtHaskell was a snap. However, if you're unfamiliar with both Qt and Haskell it will probably be confusing at first. Though I'd bet money the GTK bindings aren't any better in that regard.
I'd still say you'd be more productive with qtHaskell in the long run.

- Job


On Sat, Aug 29, 2009 at 11:03 AM, Michael Mossey <mpm@alumni.caltech.edu <mailto:mpm@alumni.caltech.edu>> wrote:

   I want to choose a GUI library for my project. Some background: I'm
   a beginner to functional programming and have been working through
   Haskell books for a few months now. I'm not just learning Haskell
   for s**ts and giggles; my purpose is to write
   music-composition-related code; in particular, I want to write a
   graphical musical score editor. (Why write my own editor, you may
   ask? Because I want to fully integrate it with
   computer-assisted-composition algorithms that I plan to write, also
   in Haskell.) I decided to use Haskell for its great features as a
   functional programming language.

   Regarding a choice of GUI library, I want these factors:

   - it needs to provide at a minimum a drawing surface, a place I can
   draw lines and insert characters, in addition to all the standard
   widgets and layout capabilities we have to come to expect from a GUI
   library.

   - This is a Windows application.

   - it needs to be non-confusing for an intermediate-beginner
   Haskeller. Hopefully good documentation and examples will exist on
   the web.

   - It might be nice to have advanced graphics capability such as Qt
   provides, things like antialiasied shapes, and a canvas with
   efficient refresh (refereshes only the area that was exposed, and if
   your canvas items are only primitives, it can do refreshes from
   within C++ (no need to touch your Haskell code at all). However I'm
   wondering if qtHaskell fits my criteria "well-documented" and "lots
   of examples aimed at beginners".

   Thanks,
   Mike
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