June 24th Wednesday (六月　二十四日　水曜日)

最新推荐文章于 2025-08-21 09:06:15 发布

原创最新推荐文章于 2025-08-21 09:06:15 发布 · 730 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#lambda #branch

本文详细解析了AMB宏的工作原理及实现方式，并通过具体示例展示了其如何在程序中进行回溯选择。AMB宏能够帮助程序实现非确定性选择，在遇到失败情况时返回并尝试其他可能的选择。

How the amb run?

(define-syntax amb
(syntax-rules ()
    ((amb alt ...)
     (let ((prev-amb-fail amb-fail))
       (call/cc
        (lambda (sk)

          (call/cc
           (lambda (fk)
             (set! amb-fail
                   (lambda ()
                     (set! amb-fail prev-amb-fail)
                     (fk 'fail)))
             (sk alt))) ...

             (prev-amb-fail)))))))

For example.

(amb #f #t)

It will be expaned as follow.

(let ((prev-amb-fail amb-fail))
(call/cc
   (lambda (sk)

     ; branch 1
     (call/cc
      (lambda (fk)
        (set! amb-fail
              (lambda ()
                (set! amb-fail prev-amb-fail)
                (fk 'fail)))
        (sk #f)))

     ; branch 2
     (call/cc
      (lambda (fk)
        (set! amb-fail
              (lambda ()
                (set! amb-fail prev-amb-fail)
                (fk 'fail)))
        (sk #t)))

     (prev-amb-fail))))

The (amb) will be expanded as follow.

(let ((prev-amb-fail amb-fail))
(call/cc
   (lambda (sk)

     (prev-amb-fail))))

The (prev-amb-fail) is invoked.

If failed, return the #f branch, and then the #t branch is began to run. The #t is selected to return.