gen.scm

(use gauche.generator)
;
#|
Scheme:generatorとdoとwhile
http://practical-scheme.net/wiliki/wiliki.cgi?Scheme%3agenerator%e3%81%a8do%e3%81%a8while#H-17qe7ru
|#
(define (generator-generate proc)
  (define next #f)
  (define return #f)
  (^[]
    (let/cc break ;; break = generatorがcallされた後に相当する継続
       (set! return break) ;; 環境を書き換え
       (if (not next)
          (begin
            (proc (^x (let/cc cc (set! next cc) (return x) ) ) )
            (return (eof-object)) )
          (next) )              ;; yieldの後に待ち構えている継続をcall
  )))

(define x #f)
(define y #f)

(set! x (generate (^[y] (y 1) (y 2) (y 3) )))
(set! y (generator-generate (^[y] (y 1) (y 2) (y 3) )))
#?=(generator->list x)
#?=(generator->list y)

(set! x (generate (^[y] (y 1) (y 2) (y 3) )))
(set! y (generator-generate (^[y] (y 1) (y 2) (y 3) )))
#?=(generator->lseq x)
#?=(generator->lseq y)

gistfile1.txt

>gosh /home/shuji/gauche/debug/gen.scm    
#?="/home/shuji/gauche/debug/gen.scm":25:(generator->list x)
#?-    (1 2 3)
#?="/home/shuji/gauche/debug/gen.scm":26:(generator->list y)
#?-    (1 2 3)
#?="/home/shuji/gauche/debug/gen.scm":30:(generator->lseq x)
#?-    (1 2 3)
#?="/home/shuji/gauche/debug/gen.scm":31:(generator->lseq y)
#?-    *** ERROR: attempt to return from a ghost continuation.
Stack Trace:
_______________________________________
  0  (format/ss (current-error-port) "#?-    ~,,,,v:s\n" (debug-print-w ...
        At line 77 of "/usr/local/share/gauche-0.9/0.9.4_pre3/lib/gauche/vm/debugger.scm"