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

From: John Clements (clements at brinckerhoff.org)
Date: Sun Sep 16 20:31:12 EDT 2012

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:

         ([((arg ...) ...)
           #`((clause.input ...) ...)])

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:

         ([((arg ...) ...)
           #`((#,(transform #'clause.input) ...) ...)])

.. 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?


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