On Oct 2, 2014, at 6:53 PM, Ryan Culpepper <ry...@ccs.neu.edu> wrote:
> On 10/02/2014 09:19 PM, Kevin Forchione wrote:
>> Hi guys,
>> Why does this appear to work? I assume it’s not a recommended approach.
>>
>> #lang racket
>>
>> (require (for-syntax syntax/parse))
>>
>> (define-syntax (mylet stx)
>> (let ([val (syntax-case stx ()
>> [(_ x) #'x]
>> [(_ x xs ...) #'(cons x (mylet xs ...))])])
>> val))
>>
>> (mylet 1 2 3) => ‘(1 2 3)
>
> It doesn't return '(1 2 3); it returns '(1 2 . 3).
>
> Other than that, the let is unnecessary, but it's just a straightforward
> recursive macro.
>
> Maybe the answer to your question is that syntax-case is nothing special;
> it's basically a version of match specialized to dealing with syntax objects.
> You can use it inside of other expressions.
> Seehttp://www.greghendershott.com/fear-of-macros/ for an explanation of how
> not-special syntax-case is.
Sorry about the typo. Yes, ‘(1 2 . 3). I was surprised that wrapping a let
around the syntax-case worked. But I suppose that define-syntax behaves
similarly to define? In other words I could have any number expressions within
the body of the define-syntax, manipulating syntax objects?
-Kevin
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