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<DIV dir=ltr align=left><SPAN class=857082717-28012014><FONT
face="Courier New"><FONT color=#0000ff size=2>Thanks.</FONT></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=857082717-28012014><FONT color=#0000ff
size=2 face="Courier New">I dont know why Racket wont release quoted literals
after disappearing, but your answer is clear.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=857082717-28012014><FONT color=#0000ff
size=2 face="Courier New">Jos</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 class=OutlookMessageHeader dir=ltr align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> Carl Eastlund
[mailto:carl.eastlund@gmail.com] <BR><B>Sent:</B> martes, 28 de enero de 2014
18:13<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>
<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="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>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>
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