Question

I have the following test example to be able to use read, but encounters some problem:

#lang racket
(struct test (num) #:prefab)
(define s3 (read (open-input-string "((AK= #s(test .)) (AV))")))
(match s3
   [`((AK= ,(struct test (val))) (AV)) (displayln val)])

It will give out read: unexpected)’`

I know it is because of the ., but my source will contain a lot of this kind of thing, then the question is that how can I read them in racket?

Thanks in advance…

Answer 1

You can disable reading dots with read-accept-dot and read-accept-infix-dot, but that just makes it an error if there’s a dot. So it sounds like you’d want to use a custom readtable here (read the guide section too):

#lang racket
(struct test (num) #:prefab)
(define rt:no-dots
  (make-readtable (current-readtable)
                  #\. 'non-terminating-macro (  _ #'|.|)))
(define (read-with-dots str)
  (parameterize ([current-readtable rt:no-dots])
    (read (open-input-string str))))
(define s3 (read-with-dots "((AK= #s(test .)) (AV))"))
(match s3
   [`((AK= ,(struct test (val))) (AV)) (displayln val)])

Alternatively, you can make the dots get treated as comments:

(define rt:no-dots
  (make-readtable (current-readtable)
                  #\. 'non-terminating-macro
                  (  _ (make-special-comment #f))))