此代码在codepad.org提供的Racket Scheme中工作,在显示消息"unexpected return"之前在连续行上显示数字1,2和3,但是相同的确切代码在ideone.com使用Chicken Scheme失败,我不明白错误消息鸡计划提供 . 如何使其与鸡计划一起使用?
(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)
1 回答
鸡需要加载syntax-case egg才能支持
syntax-case
. 但是,ideone没有安装那个鸡蛋,所以你不能在那里使用它 .因此,为了测试ideone,您将不得不将宏转换为显式重命名宏 .