On Fri, Jul 21, 2017 at 2:55 PM, William D Clinger <xxxxxx@ccs.neu.edu> wrote:
 
So far as I can see, the R7RS (small) document does not require
let-syntax and letrec-syntax to introduce new local contours, so
any code that depends on that behavior is non-portable.  As you
have pointed out, five members of WG1 did vote to break backward
compatibility with the R6RS by requiring a new local contour, but
that decision does not appear to have found its way into the R7RS
document as ratified.

No such change was required.  Both the R5RS and the R7RS say, in the first sentence of section 4.3.1, "Let-syntax and letrec-syntax are analogous to let and letrec, but they bind syntactic keywords to macro transformers instead of binding variables to locations that contain values."  Since nobody thinks (or I hope nobody thinks) that identifiers bound by let and letrec are within the existing binding contour, it follows that nobody ought to think that syntactic keywords bound by let-syntax and letrec-syntax in R[57]RS are within the existing binding contour.  This statement does not appear in R6RS, which on the contrary says that the body of let(rec)-syntax is as if wrapped in begin, which does not introduce a binding contour.

If on the other hand the R6RS position had been adopted by the WG, changes to the R7RS would have been required.  "If it was so, it might be; and if it were so, it would be: but as it isn't, it ain't."

Because there do seem to be some programmers who believe the R7RS
requires let-syntax and letrec-syntax to introduce local contours,
I have added a new --r7strict mode to Larceny that disables several
of Larceny's extensions to R7RS, including that aspect of the R6RS
semantics for let-syntax and letrec-syntax.

I think it would be better to have programs that import let(rec)-syntax from (rnrs base) exhibit R6RS behavior, and programs that import them from (scheme base) exhibit R5RS/R7RS behavior.   But of course the details of conformance or lack of it are up to the implementer.

-- 
John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
To say that Bilbo's breath was taken away is no description at all.  There are
no words left to express his staggerment, since Men changed the language that
they learned of elves in the days when all the world was wonderful. --The Hobbit