scheme - dynamic scope - why this is the return value?

Question

why under dynamic scope this code will return error for "g not defined"? when running ((ff) 5), at some point g will get a value (the f lambda) and will be inserted into the runtime stack.

(
let ((f (lambda (g)
  (lambda (n)
   (if (zero? n)
    1
    (* n ((g g) (- n 1))))))))
((f f) 5)
)

question from:https://stackoverflow.com/questions/65945323/scheme-dynamic-scope-why-this-is-the-return-value

Answer 1

With dynamic scope you don't have closures. Eg.

(define val #f)

(define (get-val val)
  (lambda ()
    val))

(define getter (get-val 5))
(getter) ; => #f

With lexical scope val from get-val lives in the returned procedure as a free variable and would return 5, but in dynamic scope it stopped existing right ather the proceudre was returned. The val referred in the procedure is whatever bound val in the dynamic scope. Eg.

(let ((val 10))
  (getter)) ; ==> 10

So val from the let became the closest binding with that name ad getter returned that.