[racket] syntax-parse question

On Aug 6, 2014, at 1:47 PM, Alexander D. Knauth <alexander at knauth.org> wrote:

> 
> 
> On Aug 6, 2014, at 1:10 PM, Kevin Forchione <lysseus at gmail.com> wrote:
> 
>> 
>> On Aug 5, 2014, at 2:21 PM, Jens Axel Søgaard <jensaxel at soegaard.net> wrote:
>> 
>>> Is this a step in the right direction?
>>> 
>>> (define-syntax (x stx)
>>> (syntax-parse stx
>>>  [(_ (y ... (z ...) w ...))
>>>   #'(xf (yf y ... (zf z ...) w ...))]))
>>> 
>>> The pattern (z ...) ... will match a sequence of lists such as (4 5 6) (7 8)
>>> but it won't match (4 5 6) 7 8 from your example.
>>> 
>>> /Jens Axel
>> 
>> Closer. It doesn’t match something like ‘( 1 2 3 (4 5 6) 7 (8 9) 10), for instance. 
> 
> For that I think you want something like this:
> (syntax-parse stx
>   [(_ (~or (z ...)
>            y)
>       ...)
>    #'(xf (yf y ... (zf z ...)))])

Sorry I forgot an ellipsis.  I meant this:
(syntax-parse stx
  [(_ (~or (z ...)
           y)
      ...)
   #'(xf (yf y ... (zf z ...) ...))])

> 
> Either that or you can use my version of syntax-parse with pattern-expanders and use ~seq-no-order:
> https://github.com/AlexKnauth/seq-no-order
> 
>> 
>> I have tried:
>> 
>> #lang racket
>> 
>> (require (for-syntax syntax/parse))
>> 
>> (define-syntax (x stx)
>> 
>>  (define-syntax-class binding
>>    #:description "binding list"
>>    (pattern (z:id ...)))
>> 
>>  (define-syntax-class or-binding
>>    #:description "binding or"
>>    (pattern (~or zb:binding y:id)
>>             #:with (z ...) #'(zb.z ...)))
> 
> This won’t work because if the y:id pattern matches instead of the zb:binding pattern, then the zb.z attribute won’t be there.
> Instead you probably wan’t this:
>  (define-syntax-class or-binding
>    #:description "binding or"
>    (pattern zb:binding
>             #:with (z ...) #'(zb.z ...))
>    (pattern y:id
>             #:with (z ...) #'(y)) ; or whatever, depending on what you want to do here
>    )
> 
>> 
>>  (syntax-parse stx
>>    [(_ (ob:or-binding ...) ...)
>>     #''ok
>>     #;#'(xf (yf ob.y ...) ...)
>>     #;#'(xf (yf ob.y ... (zf ob.z ...) ...) ...)]))
>> 
>> (define (xf . xs) xs)
>> (define (yf . ys) ys)
>> (define (zf . zs) zs)
>> 
>> (x (a))
>> (x (a b (c)))
>> (x (a b c (d e f) g h))
>> 
>> But while the pattern “appears” to match, I can’t seem to construct a template that is acceptable to syntax-parse, which doesn’t like the #:with clause on my syntax-class or-binding. I must be missing something.
>> 
>> -Kevin
>> 
>> 
>> ____________________
>>  Racket Users list:
>>  http://lists.racket-lang.org/users
> 

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