Robby, The solution you gave works with what I want to do. Thanks!
The only issue is that the rest of the codebase is already assuming that the values are stored using parameterize, so I need to change all those points to use with-continuation-mark in addition to parameterize. Is there any way to configure parameterize so it also introduces a continuation mark with the same name, and make sure the values are always synced (and so it is captured when exceptions are raised)? It would be something like: (parameterize ([param value #:also-as-continuation-mark]) e) So if I do (current-continuation-mark 'param) it will return the adequate value, in addition to being accessible as a parameter. Thanks again! -- Ismael 2011/8/10 Robby Findler <ro...@eecs.northwestern.edu> > A parameter is implementing using continuation marks (and other things). > > The short version of the story is that you want to say > > (with-continuation-mark 'key 'value e) > > instead of > > (parameterize ([param 'value]) e) > > and then when the exception is raised, you'll find that it has a field > that holds the continuation marks in effect at the point where the > value was raised. You can then use that to extract the 'value you > stored with the 'key. > > There is more information in the manuals about these primitives that > you'll want to read but don't hesitate to ask if you get stuck. > (Overall, it sounds like it should be much easier to use this approach > than the one you were thinking of before.) > > Robby > > On Wed, Aug 10, 2011 at 11:25 AM, Ismael Figueroa Palet > <ifiguer...@gmail.com> wrote: > > Hi again Robby, > > I really don't know much about continuation marks. I want the value A to > be > > embedded on the exception structure, because I check that value with a > > modified with-handlers macro. I thought that using parameters A will > behave > > like a dynamically scoped identifier. > > What are the differences, if any, of using continuation marks versus > using > > parameters?? > > Thanks > > > > 2011/8/9 Robby Findler <ro...@eecs.northwestern.edu> > >> > >> Could you put the value into a continuation mark and then, when you > >> catch the exception, look in the continuation marks to get it out > >> again? > >> > >> Robby > >> > >> On Tue, Aug 9, 2011 at 3:56 PM, Ismael Figueroa Palet > >> <ifiguer...@gmail.com> wrote: > >> > > >> > > >> > 2011/8/9 Robby Findler <ro...@eecs.northwestern.edu> > >> >> > >> >> On Tue, Aug 9, 2011 at 3:01 PM, Ismael Figueroa Palet > >> >> <ifiguer...@gmail.com> wrote: > >> >> > 2011/8/4 Robby Findler <ro...@eecs.northwestern.edu> > >> >> >> > >> >> >> The blame assignment stuff is wired pretty deep into the contract > >> >> >> system. There isn't currently any way to change that aspect of the > >> >> >> system without doing what you've done below. > >> >> >> > >> >> >> If you can say more about how/why you want to change it, tho, > there > >> >> >> maybe some extension to the current API that would work for you > and > >> >> >> that we'd be willing to maintain going forward. > >> >> > > >> >> > I defined a new-exn struct to represent exceptions and defined a > >> >> > raise > >> >> > macro > >> >> > that wraps Racket's raise to throw a new-exn value. Also, I need to > >> >> > raise > >> >> > the exception thrown by raise-blame-error inside a parameterize > >> >> > expression. > >> >> > I want to access and modify a parameter that will be used to > >> >> > construct > >> >> > the > >> >> > new-exn value. > >> >> > >> >> It sounds like you're maybe adding a field to the exn record? Can you > >> >> say more about what that field is and how you compute its value? (Or > >> >> if I'm just wrong about that?) > >> > > >> > Yes, the end result I want is to tag the exn record with a value. That > >> > value > >> > is stored in a parameter A. I want to make raise-blame-error to always > >> > raise > >> > an exception tagged with A+1. > >> > > >> > -- > >> > Ismael > >> > > >> > > > > > > > > > -- > > Ismael > > > > > -- Ismael
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