GNU Common Lisp as a porting target

When looking around at Common Lisp stuff, usually I see CMUCL and SBCL support, and rarely do I see GCL support. Maybe this is owing to what I've looked for, but it does seem like a pattern. So, if something works on CMUCL or SBCL, how difficult is it to get working on GCL? What kinds of apps are very difficult to move over? What kinds are easy? Is there some general reason why GCL doesn't seem to be as popular as CMUCL or SBCL?

Brandon Van Every           Seattle, WA

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