Thursday, 4 December 2014

HsQML released: London Edition

Last week I gave a talk to the London Haskell User Group on my GUI library HsQML. The slides are available now and a video of the talk will be posted on the group's YouTube channel in due course (I'll post again when that happens).

The most distinctive, some might say contentious, thing about HsQML compared to other Haskell GUI libraries is the split between implementing the back-end logic of an application in Haskell and describing its user interface using the QML domain specific language. This tends to frighten people off and I was at pains to stress that while QML does have inbuilt scripting capabilities, we can build real applications with just a thin layer of QML over our Haskell code.

The talk walking through the implementation of a new sample "sticky notes" application. Here, the Haskell back-end takes care of persisting the user's data in an SQLite database and exposes a data model to QML. Several alternate QML front-ends then show how the same data model can be skinned with different user interfaces.

One of the sticky notes application's front-ends uses Qt Quick Controls for a native look and feel, shown here on three platforms.

Belatedly also, I'm announcing version of HsQML which debuted on Hackage at the week-end. This minor release fixes a couple of bugs. Most notably, that fact that HsQML was leaking the QApplication object and this caused programs to occasionally crash on exit under Linux. HsQML now ships an OnExitHook() which should shutdown the Qt framework when the GHC RTS does, or alternatively you can call the new shutdownQt function to do it manually.

release- - 2014.11.29

  * Added function to shutdown the Qt framework.
  * Fixed intermittent crash on exit under Linux.
  * Fixed reanimated objects being passed to QML as undefined.
  * Fixed typo in the names of implicit property signals.

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