Okay, I gave up on the point of getting the perl bindings for gtk2 going.
It was just too much work, and would not only require getting the gtk2 bindings going, but also writing bindings for hildon, the maemo-specific stuff.
So I went to plan B, which was to reimplement a maemo-specific GUI in python that just talks to a perl back-end which takes care of all of the actual data processing. This is now well under way. A working prototype of the GUI in python is now in SVN, it can read and display calendar data, but has no edit capabilities yet. The back-end portion is just about finished, it is a mixture of code from the dayplanner perl client and the dayplanner-daemon, what’s missing there is more configuration file handling (which can’t be done yet, because I’m not quite sure what config options the maemo UI actually needs) and synchronization code.
This has helped make Day Planner even more modular. I split out some code that is useful elsewhere into a DP::CoreModules module. That module now has code that for instance handles the configuration files, parses date strings, creates config dirs, runtime module loading, summary string wrappers and localtime() wrappers. All code that can be shared (and doesn’t merit having their own module) will be put there.
I expect the maemo port to have initial editing capabilities within 1-2 weeks, depending on my workload.