Question

In lisp I can bind free variables bound in a closure like this…

(let ((x 1) (y 2) (z 3))
  (defun free-variables () (+ x y z)))

(free-variables)

results in …

6

What I want to know is if it is possible to inspect bound closure variables dynamically?

E.g.

(inspect-closure free-variables)

resulting in something like…

((x 1) (y 2) (z 3))

Thanks SO

Answer 1

Common Lisp

Access to the closure’s internal variables is only possible from functions in the same scope (See Jeff’s answer). Even those can’t query somewhere for these variables. This functionality is not provided by the Common Lisp standard.

Obviously in many cases individual Common Lisp implementations know how to get this information. If you look for example at the SLIME code (a Common Lisp development environment) for GNU Emacs, the code for inspect and backtrace functionalities should provide that. The development wants to show this – for the user/programmer the Common Lisp standard does not provide that information.