[R-SIG-Mac] Editor for R cocoa GUI?

[Matthew Fero]

Christof,
It may not be what you're asking for, but I enjoy using SubEthaEdit for 
creating R code.  It is a nice text processor and there is user 
contributed plugin which enables R syntax highlighting.  It does mean 
that you have to cut and paste your code into the R-GUI or Source your 
text files.  The program can be downloaded at the CodingMonkeys 
website:
http://www.codingmonkeys.de/subethaedit/

To add R syntax highlighting follow the developers link and download 
the "R/S-Plus" mode.  This should be placed within the application's 
Mode folder (Control+Click > Show Package Contents > 
Contents/Resources/Modes)

Matthew