[racket] reconstructing syntax objects

From: Jon Rafkind (rafkind at cs.utah.edu)
Date: Thu Nov 17 15:24:07 EST 2011

On 11/17/2011 01:20 PM, Ryan Culpepper wrote:
> On 11/17/2011 12:28 PM, Jon Rafkind wrote:
>> I have some code that deconstructs and reconstructs a syntax object. I'm
>> pretty sure this code is at fault for not adding the proper lexical
>> context back on so I get an error about 'no #%app bound'.
>> (syntax-parse form
>>   [(form ...)
>>    (with-syntax ([(form* ...) (map honu->racket (syntax->list #'(form ...)))])
>>      (datum->syntax forms
>>                     #'(form* ...)
>>                     forms
>>                     forms))]
>> I had hoped that datum->syntax would add the original lexical context
>> back on, is it not doing what I hoped?
> No, the datum->syntax there is a no-op, because #'(form* ...) is already a syntax object, and datum->syntax stops when it hits something that's already a syntax object.
> You should do something like this instead:
>   (datum->syntax forms
>                  (map honu->racket (syntax->list #'(form ...)))
>                  forms
>                  forms)

Ok thanks, that solved the problem. For future reference if I have a more complicated use case is there a way to put the original lexical context back on the new syntax object?

If such a function could exist it should go into unstable/syntax since I keep forgetting how to reconstruct the lexical context.

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