Per Bothner wrote:

 > (library "foo-counter" "scheme://r6rs"
 >    (export get-foo incr-foo)
 >    (define foo 1)
 >    (define-syntax get-foo
 >      (syntax-rules ()
 >        ((get-foo)
 >         foo)))
 >    (define-syntax incr-foo
 >      (syntax-rules ()
 >        ((incr-foo)
 >         (set! foo (+ foo 1))))))

 > In the example, get-foo and incr-foo are exported, but foo itself is
 > not.  The compiler can prove that foo is never modified expect by
 > using incr-foo.

 This statement does not seem correct to me.  This fact would only
 become apparent after use of a macro in the client code.
 The line (set! foo ....) is compiled at the use site during
 compilation of the client, not at the macro definition site.

 Regards
 Andre