Older blog entries for conrad (starting at number 62)

A Haskell template for GTK, Glade, Cairo apps

I just uploaded cairo-appbase to Hackage. This is a template for building new GUI applications using GTK, Glade and Cairo.

To install it:

  
$ cabal update $ cabal install gtk2hs-buildtools $ cabal install cairo-appbase

Then, run cairo-appbase:

The GTK widget layout is done via a Glade XML file which can be edited visually using glade. This template includes working callbacks to handle the File and Help menus and File Save/Open dialogs, with dummy handlers for selecting filenames and the Edit menu's cut/copy/paste. The main canvas uses Cairo for graphics rendering, and includes example code from the cairo package.

To build your own application on top of this, first grab the code. You can either grab it from hackage with cabal unpack cairo-appbase, or clone the git repo:

To add widgets, install glade from your distro system and run glade data/main.glade. Note that you must run cabal install to put the glade file in the correct place for your application to pick it up. To modify the code, edit src/cairo-appbase.hs. Hooking up functions to widgets is very simple: get a widget by name (which you set in glade file), and hook one of its signals (which you found in the Signals tab in glade) to an IO () action:

  
cut1

The template code includes a trivial definition of myCut:

  
myCut :: IO () myCut = putStrLn "Cut"

A real application will want to pass data to the callback. In C, this is fairly tedious as you only have a single void * to pass to callbacks as "user_data", and applications typically do lots of marshalling and unmarshalling to pass data around. In Haskell however, you can make yourself a more complex callback handler and use a curried version of it in each instance:

  
cut1 MoonPhase -> LuckyNumber -> IO () myCut project phase num = do let selection = currentSelection project when (phase == Full) howl when (num /= 7) fail doActualCut selection

Erik de Castro Lopo discussed how currying at length in his April 2006 post, GTK+ Callbacks in OCaml. The Haskell GTK+ bindings have been around a long time, but were only recently cabalized and uploaded to Hackage. I put together cairo-appbase in August 2006 when I was playing with it, but now that I have more time for Haskell I've updated it and uploaded it to Hackage. Enjoy, and hack away!

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