Though also cycle back to us. I'm curious to hear what he has to say. Shriram
On Tue, Nov 16, 2010 at 5:13 PM, Robby Findler <ro...@eecs.northwestern.edu> wrote: > That expression at the end is somehow turning a procedure back into > its quoted form. I have no idea if a Scheme that did that would be R5 > or not, but Racket definitely does not allow that (and neither did any > other programming language that I've ever worked on). > > Overall, I'd say, you should contact Aaron directly, instead of asking here. > > Robby > > On Tue, Nov 16, 2010 at 4:07 PM, John Clements > <cleme...@brinckerhoff.org> wrote: >> I'm reading Aaron Stump's "Directly Reflective Meta-Programming," and it >> appears to me that either he misunderstands Scheme, or that I misunderstand >> it. Are there many Scheme dialects in which his use of quasiquote to embed a >> 3d value would successfully pry open the syntactic term? >> >> (Excerpt below) >> >> Sorry for the OT post, >> >> John >> >> >> >> 2.1.2 Variables in Meta-Programming >> >> A meta-programming language is scope safe (or hygienic) iff variables may >> not be captured or escape their scopes during computation. Dynamic variables >> in Emacs LISP and Common LISP are a good example of a violation of scope >> safety [30, 24]. Scheme R5RS’s macro language is designed to be scope safe >> [21]. Other constructs in Scheme R5RS, however, enable violation of scope >> safety, even though the language does not have dynamic variables. For a >> violation of scope safety in spirit, though not technically, we have that >> (caddr ’(lambda (x) x)) evaluates to x. According to the R5RS language >> definition, ’(lambda (x) x) is a literal expression, and hence the >> occurrences of x in it are not variables at all, but just (unscoped) literal >> data. So in this example, a variable has been created (namely, the resulting >> unquoted x), but not by means of removing it from its scope. Using >> quasiquotation, however, the example may be modified to give a true >> violation of scope safety. The following expression extracts the variable x >> from its scope, by transforming the binding lambda expression into a piece >> of literal data, and then extracting and evaluating the quoted variable. >> >> ((lambda (y) (eval ‘(car (cdr (cdr ’,y))))) (lambda (x) x)) >> _________________________________________________ >> For list-related administrative tasks: >> http://lists.racket-lang.org/listinfo/dev >> > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/dev _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
