Racket 中的 struct 是一个宏吗?

问题描述

我记得我在某处读到它不是宏而是内置于核心语言中.类似的东西，我不确定，因为我已经记不起从哪里读到它了.那么 struct 是否是 Racket 中的宏?如果没有，为什么它被内置到核心语言中?

I remember I read somewhere it is not a macro and is built into the core language. Something like that, I am not sure, because I can no longer remember from where I read it. So is struct a macro in Racket or not? If not, why is it built into the core language?

推荐答案

一个宏；struct.rkt有

(define-syntax (struct stx)
    (define (config-has-name? config)
      (cond
       [(syntax? config) (config-has-name? (syntax-e config))]
       [(pair? config) (or (eq? (syntax-e (car config)) '#:constructor-name)
                           (eq? (syntax-e (car config)) '#:extra-constructor-name)
                           (config-has-name? (cdr config)))]
       [else #f]))
    (with-syntax ([orig stx])
      (syntax-case stx ()
        [(_ id super-id fields . config)
         (and (identifier? #'id)
              (identifier? #'super-id))
         (if (not (config-has-name? #'config))
             (syntax/loc stx
               (define-struct/derived orig (id super-id) fields  #:constructor-name id . config))
             (syntax/loc stx
               (define-struct/derived orig (id super-id) fields . config)))]
        [(_ id fields . config)
         (identifier? #'id)
         (if (not (config-has-name? #'config))
             (syntax/loc stx
               (define-struct/derived orig id fields  #:constructor-name id . config))
             (syntax/loc stx
               (define-struct/derived orig id fields . config)))]
        [(_ id . rest)
         (identifier? #'id)
         (syntax/loc stx
           (define-struct/derived orig id . rest))]
        [(_ thing . _)
         (raise-syntax-error #f
                             "expected an identifier for the structure type name"
                             stx
                             #'thing)]))))

在 Racket IDE 中，您可以使用 Open Defining File 功能来定位源代码(如果可用).

In Racket IDE, you can use the Open Defining File function to locate the source code (if available).

这篇关于Racket 中的 struct 是一个宏吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！