How to make Lisp forget about previously exported symbols?

SBCL:

* (apropos "unexport")

UNEXPORT (fbound)


* (documentation 'unexport 'function)

"Makes SYMBOLS no longer exported from PACKAGE."


* (apropos "unintern")

UNINTERN (fbound)


* (documentation 'unintern 'function)

"Makes SYMBOL no longer present in PACKAGE. If SYMBOL was present then T is
returned, otherwise NIL. If PACKAGE is SYMBOL's home package, then it is made
uninterned."

There is plenty of documentation on these issues, which you should read or reread. This package/symbol thing sounds trivial enough at first sight, but it is different enough from what other languages do to be worth some reading (i.e. trying to reuse knowledge from other languages is particularly risky when it comes to packages and symbols).

If, after reading the docs, you still have trouble, try rereading them (the experience gained by having trouble will help you focus on the relevant sections; rereading without getting into trouble between readings is not very productive IMHO).

Some links I found useful:

• http://www.lispworks.com/documentation/HyperSpec/Body/11_.htm
• http://www.gigamonkeys.com/book/programming-in-the-large-packages-and-symbols.html
• http://www.flownet.com/ron/packages.pdf