Right: it's the known unknowns that I'm worried about :) On Sat, Mar 5, 2016 at 5:29 PM, Vincent St-Amour <[email protected]> wrote: > Right, I understand that. > > Are any syntax properties used as heavily as source locations, though? > > Vincent > > > > On Sat, 05 Mar 2016 17:23:01 -0600, > Robby Findler wrote: >> >> Our experience with the source location change suggests that there are >> many places where code is implicitly relying on syntax properties not >> being preserved in byte code. This entire thread is inspired by one >> such (errortrace performance), and I know that I fixed several >> lingering bugs like this in redex well after the initial change. >> (Those bugs manifested as poor source location reporting for errors in >> redex programs). That experience makes me think we should not preserve >> all properties. (I don't have a sense of what the performance costs >> would be, but we could measure that if we cared, I think.) >> >> Robby >> >> >> On Sat, Mar 5, 2016 at 5:16 PM, Vincent St-Amour >> <[email protected]> wrote: >> > What would be use cases for ephemeral properties? >> > >> > I agree that most properties wouldn't need to be preserved, but I can't >> > think of a case where we would want to explicitly not have a property be >> > preserved. >> > >> > That, and having two kinds of syntax properties would be potentially >> > confusing. Your third solution does make the distinction pretty clear, >> > but having a single kind would make the interface simpler. >> > >> > Vincent >> > >> > >> > On Sat, 05 Mar 2016 16:23:00 -0600, >> > Matthew Flatt wrote: >> >> >> >> I agree that both of those are potential issues. I'd expect problems, >> >> but I don't know how common the problems would be. >> >> >> >> I think we would probably end up wanting ephemeral properties, anyway, >> >> so it makes more sense to be to leave ephemeral as the default and add >> >> a non-ephemeral option. >> >> >> >> At Sat, 5 Mar 2016 15:25:51 -0600, Robby Findler wrote: >> >> > Is avoiding the change to preserve of all properties a backwards >> >> > compatibility concern or a performance one? (I wouldn't ask, except >> >> > there were a surprising number of bugfixes for the source location >> >> > change.) >> >> > >> >> > Robby >> >> > >> >> > >> >> > On Sat, Mar 5, 2016 at 8:09 AM, Matthew Flatt <[email protected]> >> >> > wrote: >> >> > > At Thu, 03 Mar 2016 11:00:23 -0600, Vincent St-Amour wrote: >> >> > >> On Wed, 02 Mar 2016 22:23:29 -0600, >> >> > >> Matthew Flatt wrote: >> >> > >> > Instead of using the existence of a source location to determine >> >> > >> > where >> >> > >> > to add instrumentation, debugging should be based on the details >> >> > >> > of the >> >> > >> > source location. I'm not immediately sure of the right rule, but >> >> > >> > I'll >> >> > >> > work on it. >> >> > >> >> >> > >> Would `syntax-original?` help here? >> >> > > >> >> > > This is sort of job that `syntax-original?` was intended for, but I >> >> > > think it doesn't work well. >> >> > > >> >> > > For example, if you have >> >> > > >> >> > > (define-syntax-rule (m x) >> >> > > (* (+ x 1) 2)) >> >> > > >> >> > > and you use `m` in the same module, then you want an error for a >> >> > > non-numeric `x` to highlight `(+ x 1)`. (Since `m` doesn't guard >> >> > > against a bad `x`, it's probably not intended as an abstraction.) A >> >> > > `syntax-original?` test would limit highlighting to the uses of `m`. >> >> > > >> >> > > I think this line of thought and other experience with >> >> > > `syntax-original?` is why we haven't used it in errortrace. >> >> > > >> >> > > >> >> > > One alternative is to make errortrace add a syntax property to the >> >> > > original program, and then then only instrument forms that have the >> >> > > syntax property after expansion. That implements a notion of >> >> > > "original?" that includes templates in the source program, and it >> >> > > would >> >> > > be consistent with the old use of source locations to determine >> >> > > "original?". >> >> > > >> >> > > DrRacket compiles files with errortrace instrumentation to bytecode, >> >> > > and that suggests preserving the syntax property in bytecode. We don't >> >> > > yet have a mechanism for designating new syntax properties for >> >> > > preservation in bytecode, but it was just a matter of time... >> >> > > >> >> > > I see a few possible approaches to preserving syntax properties: >> >> > > >> >> > > * Add a parameter that lists keys to be preserved. The parameter's >> >> > > default value would be `(list 'paren-shape)`. >> >> > > >> >> > > This approach would probably work well enough for DrRacket and >> >> > > errortrace, because DrRacket could set the parameter while writing >> >> > > errortrace-instrumented bytecode. It's easy to imagine uses of >> >> > > syntax properties where that kind of configuration from the outside >> >> > > is inconvenient, though. >> >> > > >> >> > > * Introduce a naming convention for symbols as syntax properties. For >> >> > > example, a symbol that starts with the letters "preserved:" could >> >> > > mean that the property should be preserved in bytecode. >> >> > > >> >> > > A naming convention is easy, and it doesn't require cooperation >> >> > > from >> >> > > the tool that's writing bytecode. We'd still have to declare >> >> > > 'paren-shape to be a special case. >> >> > > >> >> > > * Introduce a prefab structure and a convention that a key is >> >> > > preserved if it is an instance. For example, the designated prefab >> >> > > structure type could be >> >> > > >> >> > > (struct preserved (name) #:prefab) >> >> > > >> >> > > and then '#s(preserved errortrace) as a syntax-property key would >> >> > > be >> >> > > preserved. >> >> > > >> >> > > To make this work, syntax-property keys would have to be compared >> >> > > with `equal?` instead of `eq?`, but I think that change would be >> >> > > ok. >> >> > > >> >> > > Among these options, I'm leaning toward the last one. >> >> > > >> >> > > Any other ideas? >> >> > > >> >> > > -- >> >> > > You received this message because you are subscribed to the Google >> >> > > Groups >> >> > "Racket Developers" group. >> >> > > To unsubscribe from this group and stop receiving emails from it, >> >> > > send an >> >> > email to [email protected]. >> >> > > To post to this group, send email to [email protected]. >> >> > > To view this discussion on the web visit >> >> > https://groups.google.com/d/msgid/racket-dev/56dae8b5.4e2b620a.62d8b.ffffc560SM >> >> > TPIN_ADDED_MISSING%40gmr-mx.google.com. >> >> > > For more options, visit https://groups.google.com/d/optout. >> >> >> >> -- >> >> You received this message because you are subscribed to the Google Groups >> >> "Racket Developers" group. >> >> To unsubscribe from this group and stop receiving emails from it, send an >> >> email to [email protected]. >> >> To post to this group, send email to [email protected]. >> >> To view this discussion on the web visit >> >> https://groups.google.com/d/msgid/racket-dev/56db5c48.e9a2420a.265b2.09b9SMTPIN_ADDED_MISSING%40gmr-mx.google.com. >> >> For more options, visit https://groups.google.com/d/optout.
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