On Thu, Jun 28, 2012 at 4:21 PM, Richard Kelsey <kelsey@s48.org> wrote: > Date: Thu, 28 Jun 2012 17:55:54 -0400 > From: John Cowan <cowan@mercury.ccil.org> > > Richard Kelsey scripsit: > > > For example, dynamic bindings are described using the term 'dynamic > > environment' which is itself not defined. There is a paragraph on > > how dynamic bindings interact with threads, which are not mentioned > > anywhere else in the report, but nothing is said about how dynamic > > bindings interact with call/cc or dynamic-wind. > > The intention is that dynamic bindings are implemented either directly > by dynamic-wind, or using the same underlying mechanisms. Perhaps the > report should say "as if by dynamic-wind"? > > The report should describe the semantics of dynamic variables, not one > particular implementation. The report describes the semantics in terms of dynamic extent, so the analogy to dynamic-wind seems appropriate. We do need to be careful here, and the WG has not yet had time to fully review the non-call/cc-based dynamic-binding research pointed out by Oleg. > I don't see how the R7RS dynamic variables would work with any thread > package at all, portable or non-portable, that preserves the semantics > of dynamic-wind. You can't unwind and wind on context switch, so if > you have threads you can't use dynamic-wind or any other shallow-binding > mechanism to implement dynamic variables. I think you have to use deep > binding. > > As the SRFI notes, this is currently done in various ways. > > Which SRFI? SRFI-39 on which the R7RS parameters were based. > > - Ideally, the dynamic environment and dynamic-wind would be included > > in the formal semantics. > > If anyone has a proposal here, it might be a Good Thing, but I wouldn't > know the difference between up and Tuesday when it comes to the formal > semantics, so I must decline either to write it or to edit it. > > Editorial tickets #427 and #428 created. Ballot ticket #429 for new > formal semantics created. If nobody steps up to do this and review it > before the last ballot, it will be closed. > > If the WG makes changes to the language that require changes to the > formal semantics, then they need to change the formal semantics. That > seems like part of the job. The formal semantics only covered a small subset of the language to begin with. The change in question is equivalent to adding a formal semantics for dynamic-wind, which was already missing from R5RS. I agree, of course, that we should fix this, or consider using (a subset of) the operational semantics from R6RS (which again is a subset of the language but at least has dynamic-wind). -- Alex _______________________________________________ Scheme-reports mailing list Scheme-reports@scheme-reports.org http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
