为什么Scheme不支持一流的环境？-Whydoesn'tSchemesupportfirstclassenvironments?

After more digging around I discovered this informative thread on newsnet:

经过更深入的挖掘后,我在新闻网上发现了这个信息丰富的主题:

"The R5RS EVAL and environment specifiers are a compromise between those who profoundly dislike first-class environments and want a restricted EVAL, and those who can not accept/understand EVAL without a second argument that is an environment."

“R5RS EVAL和环境说明符是那些非常不喜欢一流环境并希望限制EVAL的人与那些不能接受/理解EVAL而没有第二个参数即环境的人之间的妥协。”

Also, found this "work-around":

此外,发现这“解决方案”:

(define-syntax make-environment 
  (syntax-rules () 
    ((_ definition ...) 
     (let ((environment (scheme-report-environment 5))) 
       (eval '(begin definition 
                     ...) 
             environment) 
       environment)))) 


(define arctic 
  (make-environment 
    (define animal 'polarbaer))) 

(taken from this)

(取自此)

However, I ended up adopting a "message passing" style kinda of like the first guy suggested - I return an alist of functions, and have a generic "send" method for invoking a particular function by name... i.e something like this

然而,我最终采用了“消息传递”风格,有点像第一个人建议 - 我返回一个函数列表,并有一个通用的“发送”方法,用于通过名称调用特定的函数...即这样的东西

(define multiply
  (list
    (cons 'differentiate (...))
    (cons 'evaluate (lambda (args) (apply * args)))))

(define lookup
  (lambda (name dict)
    (cdr (assoc name dict))))

; Lookup the method on the object and invoke it
(define send
  (lambda (method arg args)
    ((lookup method arg) args))

((send 'evaluate multiply) args)

I've been reading further and am aware that there's all of CLOS if I really wanted to adopt a fully OO style - but I think even above is somewhat overkill.

我一直在阅读,并且我知道如果我真的想要采用完全OO风格,那么就有所有CLOS - 但我认为即使上面也有点矫枉过正。

Scheme has no first-class environments because of performance reasons. When Scheme was created, it wasn't the fastest language around due to nifty stuff like first-class functions, continuations, etc. Adding first-class environments would have crippled the performance even further. So it was a trade-off made in the early Scheme days.

由于性能原因,Scheme没有一流的环境。当Scheme被创建时,它不是最快的语言,因为它具有诸如一流函数,延续等等的漂亮东西。添加一流的环境会进一步削弱性能。因此,这是在早期的计划日进行的权衡。

They wrote it like that because MIT Scheme does, in fact, have first-class environments, and presumably that's what the writers were planning to teach their class with (since the book was written at MIT).

他们这样写的是因为麻省理工学院计划确实有一流的环境,并且可能是作家们计划教他们班级的(因为这本书是在麻省理工学院写的)。

Check out http://groups.csail.mit.edu/mac/projects/scheme/

查看http://groups.csail.mit.edu/mac/projects/scheme/

However, I've noticed that MIT Scheme, while still somewhat actively developed, lacks many of the features that a really modern Scheme would have, like a foreign function interface or GUI support. You probably wouldn't want to use it for a serious software development project, at least not by itself.

但是,我注意到MIT Scheme虽然仍然有些积极开发,却缺少真正现代Scheme所具有的许多功能,比如外部函数接口或GUI支持。您可能不希望将其用于严肃的软件开发项目,至少不是单独使用它。

Would a classical dispatcher function work? I think this is similar to what you're looking for.

经典的调度员功能会起作用吗?我认为这与您正在寻找的相似。

(define (scientific-library f)
  (define (scientific-square-root x) (some-scientific-square-root x))
  (cond ((eq? f 'square-root) scientific-square-root)
        (else (error "no such function" f))))
(define (fast-library f)
  (define (fast-square-root x) (some-fast-square-root x))
  (cond ((eq? f 'square-root) fast-square-root)
        (else (error "no such function" f))))

((scientific-library 'square-root) 23)
((fast-library 'square-root) 23)

You could even combine the example scientific and fast libraries into one big dispatch method:

您甚至可以将示例科学和快速库组合成一个大型调度方法:

(define (library l f)
  (define (scientific-library f)
    ...)
  (define (fast-library f)
    ...)
  (cond ((eq? l 'scientific) (scientific-library f))
        ((eq? l 'fast) (fast-library f))
        (else (error "no such library" l))))
(library 'fast 'square-root)