Chicken Scheme 中的生成器

Question

这段代码在codepad.org, displaying the numbers 1, 2 and 3 on successive lines before displaying the message "unexpected return", but the same exact code fails using Chicken Scheme at ideone.com提供的Racket Scheme中有效，我不明白Chicken Scheme提供的错误信息。如何让它与 Chicken Scheme 一起使用？

(define-syntax define-generator
  (lambda (x)
    (syntax-case x (lambda)
      ((stx name (lambda formals e0 e1 ...))
         (with-syntax ((yield (datum->syntax-object (syntax stx) 'yield)))
           (syntax (define name
             (lambda formals
               (let ((resume #f) (return #f))
                 (define yield
                   (lambda args
                     (call-with-current-continuation
                      (lambda (cont)
                        (set! resume cont)
                        (apply return args)))))
                 (lambda ()
                   (call-with-current-continuation
                    (lambda (cont)
                      (set! return cont)
                      (cond (resume (resume))
                      (else (let () e0 e1 ...)
                            (error 'name "unexpected return"))))))))))))
        ((stx (name . formals) e0 e1 ...)
          (syntax (stx name (lambda formals e0 e1 ...)))))))

(define-generator (test-gen)
  (yield 1)
  (yield 2)
  (yield 3))

(define t (test-gen))
(display (t)) (newline)
(display (t)) (newline)
(display (t)) (newline)
(display (t)) (newline)

Answer 1

Chicken 需要加载 syntax-case egg 才能支持 syntax-case。但是ideone没有安装那个egg，所以你不能在那里使用。

因此，为了在 ideone 上进行测试，您必须将宏转换为显式重命名宏。

Chicken Scheme 中的生成器

Generators in Chicken Scheme

scheme

chicken-scheme