Hi Axel,
Because gtk2hs exists and is availabe on all three platforms, everybody gets the benefit of a complete, professional interface right now, so everyone should accept it as standard and not mourn about the slight differences in UI appearnce :-)
This is actually a rather good argument in favor of GTK. However, the GTK interface does not satisfy the constraint that it must be reasonably easy to implement. If someone wants a backend for Aqua or whatever, it is extremely hard to create a gtk implementation from scratch. The world would be good place when gtk would be the standard library for writing gui's, but right now, the toolkit is mainly portable across unix platforms.
I think existance is not a very good argument.
You are right about that. I should rephrase that: "since it is implemented for two different targets, it may be a good starting point for the definition of an (L) interface" -- I think it is quite hard to even come up with some interface that is just abstract enough to be implementable by a wide range of targets and is at the same time low-level enough that it is still reasonably easy to implement.
I would like to define the portable library with techniques of the Object I/O and let everyone who has a backend (or is willing to write one) participate in its creation.
That certainly seems a good idea to me. Participation of many people with different backends is fairly essential as the (L) interface will probably change and evolve a lot when different backends are added. To get people involved though, it may be good when the 'GUI task force' is able to define some initial (L) interface that people can try to write backends for. All the best, Daan.