使用禁用的分派读取器宏创建可读表

Question

我正在创建一种基于球拍的新语言，我不希望某些#x宏工作，例如语法引用#'。我如何删除它，使#'不做语法引用，但做任何未绑定调度宏字符?

我可以通过

处理单字符宏

(make-readtable (current-readtable)
                #' #a #f) ; set ' to be the same as a normal character

但是我不知道如何为调度宏做这个

Answer 1

假设您希望将#'视为':

提供一个reader-proc，它只调用正常的read-syntax:

#lang racket/base
(define (reader-proc ch in src line col pos)
  (read-syntax src in))
(define our-readtable (make-readtable (current-readtable)
                                      #'
                                      'dispatch-macro
                                      reader-proc))
;; A `#:wrapper1` for `syntax/module-reader`, i.e. to use in your
;; lang/reader.rkt
(define (wrapper1 thk)
  (parameterize ([current-readtable our-readtable])
    (thk)))
(provide wrapper1)
;; tests
(module+ test
  (require rackunit
           racket/port)
  (parameterize ([current-readtable our-readtable])
    (check-equal? (with-input-from-string "#'foo" read)
                  'foo)
    (check-equal? (with-input-from-string "#'(foo)" read)
                  '(foo))
    (check-equal? (with-input-from-string "#'(foo #'(bar))" read)
                  '(foo (bar)))))

使用'dispatch-macro的一个稍微复杂的例子是我最近添加到#lang rackjure的lambda读取器文字支持。

---

假设您希望#'导致读错误，"bad syntax: #'":

#lang racket/base
(require syntax/readerr)
(define (reader-proc ch in src line col pos)
  (raise-read-error (format "bad syntax: #~a" ch)
                    src line col pos 2))
(define our-readtable (make-readtable (current-readtable)
                                      #'
                                      'dispatch-macro
                                      reader-proc))
;; A `#:wrapper1` for `syntax/module-reader`, i.e. to use in your
;; lang/reader.rkt
(define (wrapper1 thk)
  (parameterize ([current-readtable our-readtable])
    (thk)))
(provide wrapper1)
;; tests
(module+ test
  (require rackunit
           racket/port)
  (parameterize ([current-readtable our-readtable])
    (check-exn exn:fail? (λ () (with-input-from-string "#'foo" read)))))