[R] Packaging platform-specific functions

[jhallman at frb.gov]

I have a few functions, such as screenWidth() and screenHeight(), which
I have been able to implement for a Unix/Linux environment, but not for
Windows. (Does anyone know how to find the screen dimensions in
Windows?) 

The Writing R Extensions manual tells me how to include
platform-specific sections in documentation, and even how to have
platform-specific help files.  But it doesn't say anything about when or
how to handle platform-specific code.  In particular, how do package
writers handle functions that make sense for one platform but not for
another?  I'd like to keep a single set of source code files and
generate the Windows and Linux packages from it.

Any suggestions?

Jeff Hallman