After reading some of the original paper by Dybvig[1],
I finally managed to get the macro right. The trick
was to use "with-syntax", which -- I have to admit
-- is still a little magical to me. But by mimicking
the way the procedure "generate-temporaries" has
been used in the Dybvig's implementation of letrec,
I came up with the following solution:
(define-syntax private+public
(lambda (stx)
(define (name interface)
(define (interface-name interface)
(match interface
((head . tail)
(interface-name head))
((? symbol? name)
name)))
(datum->syntax stx (interface-name (syntax->datum interface))))
(syntax-case stx ()
((_ (private ...) ((define-variant interface . body) ...))
(with-syntax (((name ...) (map name #'(interface ...))))
#`(begin
(define name (and (defined? 'name) name))
...
(let ()
private ...
(set! name
(let ()
(define-variant interface . body)
name))
...)))))))
[1] http://www.cs.indiana.edu/~dyb/pubs/tr356.pdf
