A closure is a combination of a function and the environment containing the variables it is bound to (closed over) rather than left open (like old LISPs, like e

A closure is a combination of a function and the environment containing the variables it is bound to (closed over) rather than left open (like old LISPs, like elisp). Every function isn't a closure. In particular, elisp lambdas aren't closures because elisp is dynamically bound - the variables are open, they are not closed over. Or with another perspective, the variables are bound in the global context. Either way, elisp closures aren't. From emacs scratch buffer: (setq f (let ((x 10)) (lambda () (progn (setq x (+ x 1)) x)))) (funcall f) 11 (funcall f) 12 (setq x 20) (funcall f) 21 This is because elisp is dynamically bound - it only has one environment (in this example), the global environment (leave aside buffer-local etc. for the moment). It doesn't matter if you try to create a new environment using a lambda, the same problem still occurs: (setq g (lambda (x) (lambda () (progn (setq x (+ x 1)) x)))) (setq f (funcall g 1)) (funcall f) 22 ;; or whatever you last assigned to x, + 1