--- This message is a formal comment which was submitted to [EMAIL PROTECTED], following the requirements described at: http://www.r6rs.org/process.html --- Name : Andre van Tonder Email : andre at het.brown.edu Type : improvment Priority : medium Component : sections 9.1, 9.2 (definitions and syntax definitions) Version : 5.92 Pages : 27 Dependencies: sections 8 (expansion) and 10 (semantics)
Summary: -------- Disallow redefinitions of macros and variables in case of multiple return to RHS continuations. Description: ------------ A prior thread http://lists.r6rs.org/pipermail/r6rs-discuss/2007-March/001866.html discusses a problem that may be caused by multiple returns to library toplevel variable definitions. I would like to point out that strange behaviour might also be obtained in case of multiple returns to /macro/ definitions, also /internal/ macro definitions. I would therefore suggest outlawing multiple returns to macro defintions, library-toplevel and internal. I further suspect that allowing multiple returns to internal variable definitions are also bad, because - I suspect that it may make certain optimizations (such as detecting possibilities for inlining or direct substitution) more difficult. It is no longer sufficient to detect set! statements to determine mutability. Mutability detection becomes undecidable. - The intention of mutation does not get clearly expressed. I think it would be better if programmers were required to express all mutations using set!. In other words, I think programmers should be required to write (let () (define x) (set! x (call/cc (lambda (k) k)))) (unless (number? x) (x 1))) instead of (let () (define x (call-cc -----)) ----) Suggestion: ----------- Require a solution such as the one suggested in http://lists.r6rs.org/pipermail/r6rs-discuss/2007-March/001866.html also for internal definitions. Further outlaw multiple returns to macro definitions. This could perhaps also be succinctly expressed in the semantics by extending the current formal semantics, with the appropriate changes, to DEFINE in internal positions also. _______________________________________________ r6rs-discuss mailing list [email protected] http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
