I am creating a new language based on Racket and I don't want certain #x macros to work, such as the syntax-quote #'. How do I remove it so that #' does not do a syntax quote, but does whatever an unbound dispatch macro-char does?
I can do that with single-char macros by doing
(make-readtable (current-readtable)
#\' #\a #f) ; set ' to be the same as a normal character
but I don't know how to do this for dispatch macros.
Assuming you want #' to be treated as ':
Provide a reader-proc that simply calls the normal 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)))))
A slightly more complicated example of working with 'dispatch-macro is the lambda reader literal support I just recently added to #lang rackjure.
UPDATED
Assuming you want #' to cause a read error, "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)))))