[racket-dev] syntax parsing: must be a nice pattern-y way to do this

On Sep 16, 2012, at 5:48 PM, Ryan Culpepper wrote:

> See 'define-template-metafunction' in syntax/parse/experimental/template. Remember to change the relevant occurrences of 'syntax' to 'template'.

Neat! 

I'm guessing, though, that I probably shouldn't release planet packages that depend on experimental-mumble…

John

> 
> Ryan
> 
> On 09/16/2012 08:31 PM, John Clements wrote:
>> I want to apply a transformation to a nested pattern element.
>> 
>> To start with, suppose I have a (kind of useless) with-handlers that looks like this:
>> 
>> (with-syntax
>>          ([((arg ...) ...)
>>            #`((clause.input ...) ...)])
>>        et-cetera)
>> 
>> That is, I've basically just renamed "clause.input" to "arg".
>> 
>> But now, I want to perform some transformation on the elements. I'd like to write this:
>> 
>> (with-syntax
>>          ([((arg ...) ...)
>>            #`((#,(transform #'clause.input) ...) ...)])
>>        et-cetera)
>> 
>> .. but this fails, with the error "new-style-signals.rkt:42:30: syntax: missing ellipsis with pattern variable in template in: clause.input"
>> 
>> I can certainly work around this, by abandoning the pattern-matching slickness and just using a bunch of syntax->lists, but it seems like there must be a nicer way. Am I missing some nifty trick?
>> 
>> John
>> 
>> 
>> 
>> 
>> _________________________
>>   Racket Developers list:
>>   http://lists.racket-lang.org/dev
>> 
> 

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