<p dir="ltr">Racket will generally not release keys that are quoted literals in your program. Try building your keys using symbol->string.</p>
<div class="gmail_quote">On Jan 28, 2014 8:16 AM, "Jos Koot" <<a href="mailto:jos.koot@gmail.com">jos.koot@gmail.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<u></u>
<div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New"><span>Things work now as I expect for weak boxes, but I am
still confused about weak hash tables. I do the following:</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New"><span></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">#lang
racket</font></div>
<div> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">(define h
(make-weak-hash))</font></div>
<div> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">(define
keys<br> (for/list ((key (in-list '(a b c d e f))))<br>
(make-weak-box key) ; <--- 1<br>; key ; <--- 2<br>
))</font></div>
<div> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">(define
(enter key value)<br> (will-register will-executor value
will-proc)<br> (set! enter-counter (add1
enter-counter))<br> (hash-set! h key value))</font></div>
<div> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">(define-syntax-rule (while condition expr ...)<br> (let
loop () (when condition expr ... (loop))))</font></div>
<div> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New">(define
will-executor (make-will-executor))<br>(define (will-proc v) (set!
release-counter (add1 release-counter)) #t)<br>(define enter-counter
0)<br>(define release-counter 0)<br>(define range (in-range 6))<br>(for ((key
(in-list keys)) (value range)) (enter key (list value)))<br>(list enter-counter
release-counter) ; -> (6 0) ok<br>h ; -> hash with 6 entries, ok<br>(set!
keys #f)<span> ; discard all
keys</span><br>(collect-garbage) (collect-garbage)(collect-garbage)
(collect-garbage)<br>(while (will-try-execute will-executor))<br>(list
enter-counter release-counter) ; -> (6 6) ok<br>h ; -> empty hash,
ok</font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New"></font> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">So far ok. However, when commenting out line
<--- 1 and uncommenting line <--- 2, I would expect the same results, but
I find:</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">(6 0) ; ok</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">hash with 6 entries ; ok</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">(6 0) ; a surptrise for me</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">hash with 6 entries ; a surprise for
me</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">This is the cause of my confusion. Surely I am
misinterpreting the docs. Help much appreciated.</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New">Thanks again, Jos</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" face="Courier New"></font></span> </div><br>
<blockquote style="PADDING-LEFT:5px;MARGIN-LEFT:5px;BORDER-LEFT:#0000ff 2px solid;MARGIN-RIGHT:0px" dir="ltr">
<div lang="en-us" dir="ltr" align="left">
<hr>
<font face="Tahoma"><b>From:</b> Carl Eastlund
[mailto:<a href="mailto:carl.eastlund@gmail.com" target="_blank">carl.eastlund@gmail.com</a>] <br><b>Sent:</b> martes, 28 de enero de 2014
1:28<br><b>To:</b> Jos Koot<br><b>Cc:</b> Racket Users<br><b>Subject:</b> Re:
[racket] FW: weakly held symbols?<br></font><br></div>
<div></div>
<div dir="ltr">
<div>
<div>This isn't a typo. The docs are talking about the properties of the
symbol tables for interned and unreadable symbols. There is no symbol
table for uninterned symbols, so it wouldn't mean anything to talk about
it.<br><br></div>Here's what this means for an interned symbol: you can create
one, and while a reference to it exists, it stays in the symbol table.
Any time you intern the same string, you'll get back that symbol.
However, if all references to that symbol vanish, the symbol table is free to
release that symbol. If anyone interns the same string again later, a
new symbol will be created. For nearly all purposes, this is completely
transparent, because you couldn't possibly have a copy of the old symbol to
compare. There's almost no way to tell that the symbol you got before
and the one you got after were different. The only way you'd ever know
would be either by tracking memory use statistics, or by comparing the results
of something like eq-hash-code, neither of which should be surprising to find
out behaves impurely.<br></div></div>
<div class="gmail_extra"><br clear="all">
<div>Carl Eastlund</div><br><br>
<div class="gmail_quote">On Mon, Jan 27, 2014 at 5:53 PM, Jos Koot <span dir="ltr"><<a href="mailto:jos.koot@gmail.com" target="_blank">jos.koot@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT:1ex;MARGIN:0px 0px 0px 0.8ex;BORDER-LEFT:#ccc 1px solid"><u></u>
<div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New"><span>It
appears that my previous email was not sent completely. Sorry for that. Here
is the complete question.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Courier New"><span></span></font> </div>
<div dir="ltr" align="left"><span>
<div>
<div><font color="#0000ff" face="Courier New"><span>Hi to
all,</span></font></div>
<div><font color="#0000ff" face="Courier New"><span></span></font> </div>
<div><font color="#0000ff" face="Courier New"><span>Section "3.6 symbols" of
the Racket reference manual states:</span></font></div>
<div><font color="#0000ff" face="Courier New"><span></span></font> </div></div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0">Interned and unreadable symbols are only weakly held ... but a
symbol maay disappear when ... used as the key in a weak hash table
..."<span>.</span></font></font></font></span></div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span></span></font></font></font></span> </div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span>I would understand:</span></font></font></font></span></div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span></span></font></font></font></span> </div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span><span><font face="Courier New"><font color="#0000ff"><font size="+0">UNINTERNED and unreadable symbols are only weakly held ... but
a symbol may disappear when ... used as the key in a weak hash table
..."<span>.</span></font></font></font></span></span></font></font></font></span></div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span></span></font></font></font></span></span></font></font></font></span> </div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span>May be just a typo, but as I am not sure I understand the docs
well, I post my question here instead of posting a bug
report.</span></font></font></font></span></span></font></font></font></span></div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span></span></font></font></font></span></span></font></font></font></span> </div>
<div><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span><span><font face="Courier New"><font color="#0000ff"><font size="+0"><span>Greetings,
Jos</span></font></font></font></span></span></font></font></font></span></div></span></div></div><br>____________________<br>
Racket Users list:<br> <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a><br><br></blockquote></div><br></div></blockquote></div>
</blockquote></div>