Since Robby Findler (wisely?) declined to say much, I'll play the fool again.
Thomas Lord wrote: > I'm not sure if you are trying to say that the math is too hard > or the required labor too great. Probably both. As for the math, see below. > 1. Denotational semantics, its "least fixpoint" approach, > is the best account we have of meaning, in programming > languages. Not too many people would agree with that unqualified statement. Denotational and least fixpoint semantics may be the best accounts for some purposes, but SFAIK (and I used to know quite a bit about this) they don't work very well for languages with non-flat domains (e.g. higher order functions) and nondeterministic semantics. In other words, they don't work very well for Scheme. To simplify the technical problem only slightly, it's hard to define an adequate ordering relation that won't conflate the possible results x and y with all possible results that lie between x and y in the ordering. You can work around that somewhat by using operational denotations, but that approach tends to have all of the disadvantages and none of the advantages of using an operational approach. That is why the editors asked Robby Findler and Jacob Matthews to write an operational semantics for R6RS, replacing the denotational semantics of previous reports. As for the observably sequential functions, they form a proper subspace of the continuous function domains that are normally used in denotational semantics. They exclude things like parallel or, which have to do with the failure of the obvious denotational semantics for deterministic Lisp-like languages to be fully abstract. Robby and Matthias have been using observably sequential functions in their research, and may have some results or speculation that might bear on the problem; you'd have to ask them, as I have just told you almost all I know about observably sequential functions. Will _______________________________________________ r6rs-discuss mailing list [email protected] http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
