Nick Name wrote:
[...] This raises the problem: what if I have also "instance Positioned Window"? Well, this problem has many solutions, the simplest of wich is *not* to have statically read-only attributes. I would rather try other solutions, however they might complicate the class and type hierarchy.
What do you all think about this?
I think that the distinction (read-only, write-only, read-write) is very important for a good API design: Runtime tests are evil when errors could have been caught at compile time. The poor programmer would be forced to consult the documentation for every widget to see if getting and/or setting a particular attribute/property is allowed or not. :-P My OpenGL/GLUT binding relies very heavily on "state variables", which are very similar to the stuff in HToolkit and other proposals on this GUI list: http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/OpenGL/Graphics/Rendering/OpenGL/GL/StateVar.hs?rev=1.6&content-type=text/x-cvsweb-markup The main difference is that there is no `w' (widget) argument, because OpenGL/GLUT/OpenAL/... are based on an implicit context, which can be changed separately outside the core API. In the case of OpenGL, the context is the whole OpenGL state machine, which is typically a window-local entity managed by a toolkit. Because of this, my get/set API is a bit simpler, but I'm quite interested in a general (H98 conformant!) API for use in the GUI APIs and my stuff. Cheers, S.