Per Bothner wrote:

 > Am I correct in understanding that any quoted S-expressions, in either a
 > macro "parameter" or in a template, is copied?

 You are.

 > I don't know if this is a big deal, but it breaks pair identity in cases
 > where it is preserved in existing implementations.  This seems to make
 > SRFI-72 essentially incompatible with SRFI-38, in the sense that you
 > can't use of SRFI-38 shared structure in programs (though it is still
 > available for external data).  And of course cycles are prohibited.

 Good point.  I assume you mean expressions like

   (define ones (quote #0=(1 . #0#)))

 The procedures that would have to be changed to support this are the
 current implementations of datum->syntax and syntax->datum, essentially
 lifting the algorithm of SRFI-38 in the way you suggest.

 Regards
 Andre