At Thu, 18 Jun 2009 16:27:02 -0400, Carl Eastlund wrote: > On Thu, Jun 18, 2009 at 4:03 PM, Matthew Flatt<mfl...@cs.utah.edu> wrote: > >> > >> I see. I have contracts set up to accept only symbols and keywords > >> whose names are ASCII strings; I was planning to use a weak, eq?-based > >> hash of their names to shortcut the test. Apparently, though, I > >> cannot get eq?-unique names for symbols and strings. If I hash the > >> symbols and keywords themselves, I believe the weak table can never > >> reclaim the space (since interned symbols and keywords are forgeable); > > > > 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? _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
