Are you trying to figure out whether a particular file is the "main
script" as opposed to being loaded from some other script?
One way to do this is to check your own variable *main* and bind it if
it is not bound already. This is portable.
Another way is to use SYS::*LOAD-LEVEL*, which is bound to incremented
values by LOAD.
Yet another way is EXT:ARGV http://clisp.org/impnotes/environment-enq.html#argv
2 years ago you asked about this here:
can you offer a better rationale than then?