Portable Windows for Common Lisp?

[kddlab!harl.hitachi.co.jp!mklein@uunet.UU.NET]

I would like to incorporate a machine-portable windowing capability
in my Common Lisp program (e.g. portable between Explorer, Symbolics,
SUN with CL interpreter). I don't want to have to rewrite my window-
based code every time I change machines, and would appreciate an easy
to use (high-level interface) from Common Lisp. Full functionality
like displaying windows on other machines would be nice; mouse-based
interaction is essential. Free/cheapware is of particular interest.

For example, I've heard X windows is an emerging standard used on 
many machines, and I have gotten the impression that some vendors 
are supplying high level CL interfaces to X windows. 

Could someone give me a pithy description of what my options are?

Currently I am using a Symbolics Lisp machine, "soon" to be upgraded
to Genera 8.0.

Sorry to be asking such an elementary question. I have had trouble getting
a coherent picture from the spate of messages on windowing systems.

		Mark Klein, Ph.D.
		Hitachi Ltd.
		Advanced Research Lab
		Hatoyama, Sataima 350

		mklein@harl.hitachi.co.jp
		0492-96-6111 ext. 341