;; Dynamic versus lexical scope
;; see librep.info: Variables, Scope and Extent
(require 'stdlib)

;; defvar defines a special (i.e. dynamically scoped) variable
(defvar a 'aap)
;; define defines a lexically scoped variable
(define b 'noot)
(setq c 'mies)

(defun f ()
  (let ((a 'wim)
        (b 'zus)
        (c 'jet))
    (printf "%s %s %s\n" a b c)
    (g)))

(defun g ()
  (printf "%s %s %s\n" a b c))

;; prints: wim zus jet, wim noot mies
;; when g is invoked from f, a stays dynamically bound to its value in the
;; closure of f, and b is lexically bound to the global b.
(f)
;; prints: aap noot mies
(g)

;; example of a peristent lexical binding. The counter variable is only
;; accessible from forms written inside the let form declaring it.
(let ((counter 0))
  (defun count ()
    (setq counter (1+ counter))
    counter))

(puts (count))                          ; => 1
(puts (count))                          ; => 2
(puts (count))                          ; => 3