There is a math node that has less than and greater than functions. There are other nodes that return Boolean values for various tests. They are in the wiki under cycles/reference.
I have already tried to use the math node.
That would still mean that i need to supply a value in the group input. What i need is a checkbox in the group input itself instead of a socket or a value input.
eg. check box to switch between an opaque or transparent shader with nothing in between.
I hope you get what you want it sounds like a nice addition if you are distributing your nodegroups to people who don’t know how to use nodes, but I personally don’t see the difference between a checkbox and a two position sliding switch.