Hi Will, Thank you for the detailed review!
On Thu, Nov 27, 2014 at 8:50 AM, William Cushing <william.cush...@gmail.com> wrote: > I'm trying to grok the formal semantics section, 7.2, of r7rs small. > > It seems to me there are numerous small errors, but perhaps I'm just > confused. > > I don't see any errata for the formal section on the web page; and I > couldn't find a better place to submit bugs....so, here goes: > > > ;;;; > ;; car-internal > ;;;; > > As written, the declared type of car-internal is "expression-value to > expression-continuation to command-continuation" (E->K->C). > > However, the definition starts with "lambda ewk", and results in calling > hold on two > args (and that results in a command-continuation). So the type of the > definition is "expression-value to dynamic-point to expression-continuation > to command-continuation" (E->P->K->C). > > Based on how car-internal is called, the fix appears to be: simply delete > the w in the definition (that is, delete the \omega). In other words, the > type statement is correct, but the definition is not. > The addition of the w (dynamic point) arguments comes from reference 40, "How to Add Threads to a Sequential Language Without Getting Tangled Up" by Gasbichler, et al. I think we trusted too much that any errata in that would have turned up by now and didn't do a thorough enough review on our end. For this case I think you are exactly correct, and we should delete the \omega. ;;;; > ;; valueslist > ;;;; > > As-is the definition of valueslist resembles: > > ;; E->K->C > (define valueslist > (lambda (e k) > (if (pair? e) > (cdr-internal e > (lambda (e*) ; (0) > (valueslist e* ; (1) > (lambda (e**) > (car-internal e > (single (lambda (e+) ; (2) > (k (list* e+ e**)))) ; (3) list*=cons > )) > )) > ) > ;; not a pair > (if (null? e) (k (list)) (error "non-list argument to > *values-list*")) > ))) > > At (1), e* will be a (singleton) sequence of values, but values-list does > not accept a sequence of values as its first argument. Since car-internal > and cdr-internal work by sending a singleton sequence to their > expression-continuation, it seems that (1) should be: > > (valueslist (first e*) ...) ; (A) > > Alternatively, (0) could be: > > (single (lambda (e++) (valueslist e++ ...)) ; (B) > > That is perhaps more pleasing, since it would be symmetric with how > car-internal is called at (2). > > On the other-hand, calling internal functions (bypassing type-checks) > suggests complete confidence, and so perhaps bypassing > argument-count checking (from single) is desirable as well. If so, > then (A) is preferable, and for symmetry, likewise (2) should be: > > (lambda (e***) (k (list (first e***) e**) )) ; (A') > Again I think you're analysis is spot-on. I prefer (A'). Incidentally, list->values seems more Scheme-y than valueslist. > The RnRS denotational semantics has always avoided punctuation in identifiers, probably because it uses infix notation. This rule was only broken in the new change for c[ad]r-internal (arguably in the spirit of Dylan). This is all I have time for now, and I'll be traveling the next week, but will get back to this afterwards. Thanks again! -- Alex
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