One new important feature of development version of Sler is the possibility to control shader arguments generation. Now only marked inputs of nodes are translated into shader arguments in generated RSL code. Also you can set the storage class for arguments (uniform or varying) and mark argument as output. In future when creating custom channels for nodes is implemented you will be able to use really arbitrary output variables (AOV) but now you can use only existing channels.
This video demonstrates this feature:
Or you can download it here.
You can get latest development version of Sler with this command:
cvs -z3 -d:pserver:email@example.com:/cvsroot/ribkit co -P sler
Or you can use graphical tools (usually on Windows) like WinCVS or TortoiseCVS