As for CL packages, I've decided I don't really like the way they work. If a file is compiled, then (in-package foo) is only guaranteed to work if it appears at the top level. So...
(if (eq x 10) (in-package foo) (in-package bar))
works in an interpreted file, but the behaviour is undefined if the file is compiled. CLISP handles both cases fine.
Also in CL, the value of package* doesn't always correspond to the actual current package. For example
(setf x "I'm in the default pacakge!")
(setf foo::x "I'm in the FOO package!")
(setf *package* foo)
(print *package*)
(print x)
does this when interpreted
#<PACKAGE FOO>
"I'm in the FOO package!"
but this when compiled
#<PACKAGE FOO>
"I'm in the default pacakge!"
Either the package should be determined at eval-time (as was your suggestion) or the user should be forced to use read macros like #: and #.(in-package ...) to switch packages at read time. The CL solution is an ad-hoc compromise between the two.
Forcing the user to keep using read macros doesn't feel quite right. Personally I'm more for using 'eval-cxt objects, which would do the assignment from plain symbols to qualified symbols, and keep track of the current package.
Of course, using 'eval-cxt raises questions about static whole-program compilation, I think. Hmm. I haven't thought deeply about that yet.
