(with-values () (resume (calling-coroutine) object #t) #f))
+(define (reduce-generator func init gen)
+ ;; Call FUNC for each item in the generator GEN.
+ ;;
+ ;; We maintain a STATE, which is initially INIT. For each ITEM produced by
+ ;; the generator, we replace the state by (FUNC ITEM STATE); finally, we
+ ;; return the final state.
+
+ (let loop ((state init))
+ (with-values (item any?) (resume gen)
+ (if any?
+ (loop (func item state))
+ state))))
+
(define (list-generator gen)
;; Collect the elements generated by GEN into a list and return it.
- (let loop ((l '()))
- (with-values (it any?) (resume gen)
- (if any?
- (loop (cons it l))
- (reverse l)))))
+ (reverse (reduce-generator cons '() gen)))
(define (same-generators? gen-a gen-b)
;; Return whether GEN-A and GEN-B generate the same elements in the same
(define (main args)
(cond ((null? args) (error "bad args"))
((null? (cdr args))
- (do ((l (list-generator (fringe (parse-tree (car args)))) (cdr l)))
- ((null? l))
- (write-char (car l)))
+ (reduce-generator (lambda (ch ?) (write-char ch)) #f
+ (fringe (parse-tree (car args))))
(newline))
((null? (cddr args))
(display (if (same-generators? (fringe (parse-tree (car args)))