Thanks Robby - I will dig into these papers to learn more about custodians.  Thanks, yinso <div>On 4/16/07, Robby Findler <<a href="mailto:robby@cs.uchicago.edu"> robby@cs.uchicago.edu</a>> wrote:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Oh! Custodians are the mechanism we use to identify "principal"s for the purpose of reclaiming resources. Threads are one such resource. I suggest that you read these two papers to get an idea of the pragmatics of custodians:   <a href="http://www.ccs.neu.edu/scheme/pubs/icfp99-ffkf.pdf"> http://www.ccs.neu.edu/scheme/pubs/icfp99-ffkf.pdf</a>   <a href="http://www.cs.utah.edu/plt/publications/pldi04-ff.pdf">http://www.cs.utah.edu/plt/publications/pldi04-ff.pdf</a> They are really quite different than the other things (let, fluid-let, parameterize) you are asking about. Robby On 4/16/07, Yin-So Chen <<a href="mailto:yinso.chen@gmail.com">yinso.chen@gmail.com</a>> wrote: > They are both mentioned under the thread chapter in mzscheme doc hence I > thought they were related ;)  Under what situation do I need to think about > custodians? > > Thanks, > yinso > > >  On 4/16/07, Robby Findler <<a href="mailto:robby@cs.uchicago.edu"> robby@cs.uchicago.edu</a>> wrote: > > No, parameterize doesn't use custodians. They're independent of each > other. > > > > Robby > > > > On 4/16/07, Yin-So Chen < <a href="mailto:yinso.chen@gmail.com">yinso.chen@gmail.com</a>> wrote: > > > Thanks Robby/Carl (and Eric for answering privately) - > > > > > > here's a related question:  Does parameterize automatically uses a > custodian > > > (e.g. current-custodian) to manage resources or custodians have to be > used > > > explicitly? > > > > > > > > > On 4/16/07, Robby Findler < <a href="mailto:robby@cs.uchicago.edu">robby@cs.uchicago.edu</a>> wrote: > > > > Another difference between parameters and fluid-let: in a fluid-let > > > > the values are not thread local, but in a parameter they are. > > > > > > > > Robby > > > > > > > > On 4/16/07, Carl Eastlund <<a href="mailto:cce@ccs.neu.edu">cce@ccs.neu.edu</a> > wrote: > > > > > On 4/16/07, Yin-So Chen < <a href="mailto:yinso.chen@gmail.com">yinso.chen@gmail.com</a>> wrote: > > > > > > What is the difference between using let vs parameterize? > > > > > > > > > > Let operates on bindings.  It creates a new name and binds it to a > > > > > value.  This affects code directly within the let-body that refers > to > > > > > the same name, providing it is not bound again ("shadowed") inside > the > > > > > let. > > > > > > > > > > Parameterize operates on parameters, which are values.  It takes an > > > > > existing parameter and makes it return a different value during the > > > > > execution of the body of the parameterize.  This affects any code > > > > > called during that execution, even if it's in a different function, > > > > > module, whatever, so long as it uses the same parameter value. > > > > > > > > > > > It seems that one can use let to manipulate parameter objects (at > > > least > > > > > > scheme doesn't forbid it) - any issues with using it? > > > > > > > > > > Let does not manipulate values at all.  It just binds names to > > > > > existing values.  It never changes values or their contents. > > > > > > > > > > >  How do I know whether or not something is a parameter versus a > > > variable? > > > > > > > > > > You could ask the same thing about numbers vs variables, or strings > vs > > > > > variables.  A variable is a name for a value.  That value might be > > > > > anything: number, string, list, parameter, etc.  But you should be > > > > > careful never to confuse the name with what it refers to. > > > > > > > > > > And in response to the followup email: fluid-let, like let, operates > > > > > on variables (names), not values.  Hence it would not be an > > > > > "extension" to make it work on parameters.  If you give the name of > a > > > > > parameter to fluid-let, it will change which parameter that name > > > > > refers to, not the contents of the current parameter. > > > > > > > > > > -- > > > > > Carl Eastlund > > > > > _________________________________________________ > > > > >   For list-related administrative tasks: > > > > > > <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a> > > > > > > > > > > > > > > > > > > > > > -- > > > <a href="http://www.yinsochen.com">http://www.yinsochen.com</a> > > > ...continuous learning... > > > > > >  -- > > <a href="http://www.yinsochen.com"> http://www.yinsochen.com</a> > ...continuous learning... </blockquote></div> -- <a href="http://www.yinsochen.com">http://www.yinsochen.com</a> ...continuous learning...