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. -- 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/m2twkkjygp.wl-stamourv%40eecs.northwestern.edu. For more options, visit https://groups.google.com/d/optout.
