Re: [Scheme-reports] Legacy caar to cddddr

[Denis Washington <denisw@x>]

Am 22.10.2011 19:55, schrieb John Cowan:
> Andre van Tonder scripsit:
>
>>       (define-syntax do
>>        (er-transformer
>>         (lambda (exp r c)
>>           (or (and (pair? (cdr exp))
>>                    (pair? (cddr exp)))
>>               (syntax-error))
>>           (let ((specs (cadr exp))
>>                 (end (caddr exp))
>>                 (body (cdddr exp))
>>                 (loop (syntax loop)))
>
> It's not obvious why this is better than pattern-matching, though.

Also, a destructuring let form would be a much better solution. For 
instance, in Clojure you can write something like:

(let [[_ specs end & body] exp]
   ...)

We could have something similar in WG2:

(let (((_ specs end . body) exp))
   ...)

Even better, we could also have an "if-let" form whose execution path 
depends on whether the destructuring is possible:

(if-let (((_ specs end . body) exp))
   ...
   (syntax-error))

Such destructuring forms would remove most reasons for having cadr etc. 
in the standard.

Regards,
Denis

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