; this is the only case where walk terminates naturally
[(null? l) '()]
[(atom? (car l)) (begin
- (let/cc k2
+ (let/cc k2 (begin
(set! resume k2) ; now calling resume with val will ignore val
- ; and continue with the second line of (begin ... (walk (cdr l)))
+ ; and continue with the final line of (begin ... (walk (cdr l)))
; when the next line is executed, yield will be bound to k1 or k3
- (yield (car l)))
+ (yield (car l))))
; the previous yield line will never return, but the following line will be executed when resume is called
(walk (cdr l)))]
[else (begin
(walk (car l))
(walk (cdr l)))]))]
[next (lambda () ; next is a thunk
- (let/cc k3
+ (let/cc k3 (begin
(set! yield k3) ; now calling yield with val will return val from the call to next
; when the next line is executed, resume will be bound to k2
- (resume 'blah)))]
+ (resume 'blah))))]
[check (lambda (prev)
(let ([n (next)])
(cond
; n will fail to be an atom iff we've walked to the end of the list, and (resume 'blah) returned naturally
[else #f])))])
(lambda (lst)
- (let ([fst (let/cc k1
+ (let ([fst (let/cc k1 (begin
(set! yield k1) ; now calling yield with val will bind fst to val and continue with the (cond ...) block below
(walk lst)
; the next line will be executed only when lst contains no atoms
- (yield '()))])
+ (yield '())))])
(cond
[(atom? fst) (check fst)]
[else #f])