S9fES **              ==>  object
      *extensions*    ==>  list
      *library-path*  ==>  string
      *loading*       ==>  boolean

These are dynamic variables defined at the top level of S9fES.
** evaluates to the result most recently displayed at the REPL.

*EXTENSIONS* lists the extension procedures provided by the
extended interpreter (if any).

*LIBRARY-PATH* is a string containing the value of the
S9FES_LIBRARY_PATH environment variable as initialized when the
interpreter launches (or a reasonable default value).

*LOADING* is set to #T when the interpreter loads a file and
otherwise to #F. Altering the value of *LOADING* by a program
will lead to undefined behavior of S9fES.

(cons 1 2)      ==>  (1 . 2)
(car **)        ==>  1

*extensions*    ==>  ()

*library-path*  ==>  ".:~/.s9fes:/u/share/s9fes"

*loading*       ==>  #f

If you want to change the values of these variables temporarily at
run time, you need the FLUID-LET syntax, which is contained in the
S9fES extension library:

(let ((*library-path* "some-new-path"))
  (load-from-library "in-new-path.scm"))       ==>  error

(fluid-let ((*library-path* "some-new-path"))
  (load-from-library "in-new-path.scm"))       ==>  OK
