如何在球拍中使用管道和自定义端口

Question

我试图在球拍中使用自定义端口或管道。我想写一个消息到管道，管道检查消息，并根据消息，它返回另一个消息或某个值。

我已经试过这样的事情：

(define (write-s msg) 
    (let-values ([(in-port transmitting) (make-pipe)] 
       [(receiving out-port) (make-pipe)]) 
    (write msg out-port) 
     (let ((message (read receiving))) 
     (if (equal? message '(DOGE)) 
      (write '(SO AMAZE) transmitting) 
      'do-nothing) 
     (if (equal? message '(MUCH PIPES)) 
      (write '(WOW RACKET) transmitting) 
      'do-nothing)) 
     (read in-port))) 

Answer 1

我建议定义一个简单的辅助功能，make-codec-input-port，让您从原始输入端口和一个“编解码器”功能创建一个输入端口。这里的关键点 - 对于我来说，make-pipe的Racket文档不是很明显 - 您想要运行调用编解码器功能的thread。

在这里我展示了一个普通的编解码器，它可以用#\b替代每个#\a字符。你可以改变它的match声明来做更有趣的事情。

#lang racket 

;; Given an input-port and a codec function, return a new input-port 
;; that is the encoded version. `codec` is (input-port? output-port? 
;; -> any). For example can be deflate, inflate, gzip-through-ports, 
;; gunzip-through-ports, copy-port (the identity function for this), 
;; or your own such function. 
(define codec-buffer-size (make-parameter 1024)) 
(define (make-codec-input-port in codec [name #f]) 
    (define-values (pin pout) (make-pipe (codec-buffer-size) name name)) 
    (thread (lambda() 
      (codec in pout) 
      (close-output-port pout))) 
    pin) 

;; Example of a codec function. 
(define (replace-a-with-b in out) ;; (input-port? output-port? -> any) 
    (let loop() 
    (define ch (read-char in)) 
    (unless (eof-object? ch) 
     (write-char (match ch 
        [#\a #\b] 
        [x x]) 
        out) 
     (loop)))) 

;; You could also write the codec function a bit more simply using 
;; `in-port`: 
(define (replace-a-with-b in out) ;; (input-port? output-port? -> any) 
    (for ([ch (in-port read-char in)]) 
    (write-char (match ch 
        [#\a #\b] 
        [x x]) 
       out))) 

;; Example direct use of the codec function. 
(let() 
    (define orig-in (open-input-string "axaxax")) 
    (replace-a-with-b orig-in (current-output-port))) 
;; => bxbxbx 

;; Example use of the encoded input port. With this, a user of the 
;; port need not know anything about the codec function. 
(let() 
    (define orig-in (open-input-string "axaxax")) 
    (define encoded-in (make-codec-input-port orig-in replace-a-with-b)) 
    (port->string encoded-in)) 
;; => "bxbxbx"