[R6RS] syntax-case semantics

[dyb at cs.indiana.edu]

> At least in theory, it means that writing reusable and reliable 
> syntax-generating procedures for use by macros should be trickier, since 
> such a procedure has to take special steps to avoid having variables it 
> introduces capture variables from the invoking macro's syntactic 
> environment.

That's conceivable, but I believe it's a non-problem in practice, and I
hate to complicate the common case to fix a non-problem.  The hygiene
problem for macros is a real and common problem in practice, or was before
hygienic expansion.

> Might it make sense to add to traditional syntax-case something like a 
> FRESH-SYNTAX form, which uses the SRFI 72 semantics?  That would allow 
> the sorts of problem examples given in the SRFI to be written safely and 
> easily.

That's a good idea, worth considering anyway.

Kent