[racket] FW: weakly held symbols?

Because quote maintains its own interning table, I believe.  Also, at a
REPL, the syntax of the quote may still be accessible.
On Jan 28, 2014 1:37 PM, "Jos Koot" <jos.koot at gmail.com> wrote:

>  Thanks.
> I dont know why Racket wont release quoted literals after disappearing,
> but your answer is clear.
> Jos
>
>  ------------------------------
> *From:* Carl Eastlund [mailto:carl.eastlund at gmail.com]
> *Sent:* martes, 28 de enero de 2014 18:13
> *To:* Jos Koot
> *Cc:* Racket Users
> *Subject:* RE: [racket] FW: weakly held symbols?
>
>  Racket will generally not release keys that are quoted literals in your
> program.  Try building your keys using symbol->string.
> On Jan 28, 2014 8:16 AM, "Jos Koot" <jos.koot at gmail.com> wrote:
>
>>  Things work now as I expect for weak boxes, but I am still confused
>> about weak hash tables. I do the following:
>>
>> #lang racket
>>
>> (define h (make-weak-hash))
>>
>> (define keys
>>  (for/list ((key (in-list '(a b c d e f))))
>>   (make-weak-box key) ; <--- 1
>> ;  key ; <--- 2
>>   ))
>>
>> (define (enter key value)
>>  (will-register will-executor value will-proc)
>>  (set! enter-counter (add1 enter-counter))
>>  (hash-set! h key value))
>>
>> (define-syntax-rule (while condition expr ...)
>>  (let loop () (when condition expr ... (loop))))
>>
>> (define will-executor (make-will-executor))
>> (define (will-proc v) (set! release-counter (add1 release-counter)) #t)
>> (define enter-counter 0)
>> (define release-counter 0)
>> (define range (in-range 6))
>> (for ((key (in-list keys)) (value range)) (enter key (list value)))
>> (list enter-counter release-counter) ; -> (6 0) ok
>> h ; -> hash with 6 entries, ok
>> (set! keys #f) ; discard all keys
>> (collect-garbage) (collect-garbage)(collect-garbage) (collect-garbage)
>> (while (will-try-execute will-executor))
>> (list enter-counter release-counter) ; -> (6 6) ok
>> h  ; -> empty hash, ok
>>
>> So far ok. However, when commenting out line <--- 1 and uncommenting line
>> <--- 2, I would expect the same results, but I find:
>>
>> (6 0) ; ok
>> hash with 6 entries ; ok
>> (6 0) ; a surptrise for me
>> hash with 6 entries ; a surprise for me
>>
>> This is the cause of my confusion. Surely I am misinterpreting the docs.
>> Help much appreciated.
>>
>> Thanks again, Jos
>>
>>
>>
>>
>>  ------------------------------
>> *From:* Carl Eastlund [mailto:carl.eastlund at gmail.com]
>> *Sent:* martes, 28 de enero de 2014 1:28
>> *To:* Jos Koot
>> *Cc:* Racket Users
>> *Subject:* Re: [racket] FW: weakly held symbols?
>>
>>   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.
>>
>> 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.
>>
>> Carl Eastlund
>>
>>
>> On Mon, Jan 27, 2014 at 5:53 PM, Jos Koot <jos.koot at gmail.com> wrote:
>>
>>>  It appears that my previous email was not sent completely. Sorry for
>>> that. Here is the complete question.
>>>
>>>  Hi to all,
>>>
>>> Section "3.6 symbols" of the Racket reference manual states:
>>>
>>> Interned and unreadable symbols are only weakly held ... but a symbol
>>> maay disappear when ... used as the key in a weak hash table ...".
>>>
>>> I would understand:
>>>
>>> UNINTERNED and unreadable symbols are only weakly held ... but a symbol
>>> may disappear when ... used as the key in a weak hash table ...".
>>>
>>> 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.
>>>
>>> Greetings, Jos
>>>
>>> ____________________
>>>   Racket Users list:
>>>   http://lists.racket-lang.org/users
>>>
>>>
>>
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