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" <[email protected]> wrote:
> Thanks. > I dont know why Racket wont release quoted literals after disappearing, > but your answer is clear. > Jos > > ------------------------------ > *From:* Carl Eastlund [mailto:[email protected]] > *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" <[email protected]> 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:[email protected]] >> *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 <[email protected]> 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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