Question about Unix file paths

I think you should test for OS ( R.Version()$os )

The special meaning of "c:file" on Windows does not exist on
Unix, even if the filesystem is on a mounted Windows partition.

The patch does that implicitly by an "#ifdef Win32" in the source
code, an explicit check isn't needed.

If there are strange situations where the default handling of path
separators doesn't work, the user can always put together the path
using paste().  Users could have done that in Windows for paths like
C: or C:\, but those are common enough that I think it's reasonable to
handle them explicitly.

Duncan Murdoch