On Thu, Jun 18, 2009 at 4:34 PM, Matthew Flatt<mfl...@cs.utah.edu> wrote: >> > >> > No --- symbols and keywords are GCed, so a weak hash table would work. >> > >> > (And weakness in hash tables isn't about whether you could synthesize >> > the key. We have `equal?'-based hash tables with weak keys, after all.) >> >> I see. I tried to demonstrate this one way or another to myself with >> a weak box containing a symbol and a call to collect-garbage, and the >> box never "emptied". Perhaps that experiment was not conclusive; >> maybe collect-garbage doesn't guarantee emptying of all weak boxes, or >> I had a reference to the symbol lying around somewhere I didn't know >> about. > > I tried this in the MzScheme and DrScheme (module language) REPLs: > > > (define b (make-weak-box 'not-used-elsewhere)) > > (weak-box-value b) > not-used-elsewhere > > (collect-garbage) > > (weak-box-value b) > #f > > Did you try the same thing?
Nope. I put the first line in the definitions window, which of course put the symbol in the compiled version of the module, thus preventing it from being GC'd. Oops. --Carl _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
