lexical scope and dynamic extent

[Daniel L. Weinreb <DLW@SCRC-QUABBIN.ARPA>]

In the Symbolics system, interpreted, you get

>>Error: The GO tag L is no longer dynamically active

Compiled, you get a less-comprehensible error message:

>>Error: Attempt to %UNWIND-INTO-FRAME-AT-PC to a frame not running a
compiled function

In both cases, the system has detected that something's wrong.  In the
latter case, it goes to look for the tag, and finds an interpreted frame
where it expected a compiled frame, because the outer frame is gone.  To
improve the error message, we'd probably have to add some more
debugging-info (debugging-info is extra structure that lives with a
compiled code object to help the system create error messages and to
help various debugging tools figure out what's happening, among other
things).  It wouldn't be particularly hard.