(gensym) generates something that cannot be created again in anyway. Even it is printed as 'g1753, that doesn't mean typing 'g1753 will get the same thing, nor that (string->symbol "g1753") will either. This is the whole point of (gensym).
The Web server (basicaly) runs symbol->string to create the page and then string->symbol later to turn the HTTP request in to the symbol. When you did that to your gensym'd symbol, you got the same thing that came out of the HTML. As for how it works... you can think of symbols as just pointers to table entries that contain the actual text. (gensym) basically just uses a different table, so it's impossible for a pointer in one table to be the same as a pointer in the other table even if the text is the same on both table entries. Jay On Sun, Jul 31, 2011 at 9:07 PM, J G Cho <g...@fundingmatters.com> wrote: > That sounds like a black magic. I am almost tempted to ask how it's done. > > I imagined (gensym) would generate some unique sequence not used so > far. Why would this approach not work? > > 2011/7/31 Jay McCarthy <jay.mccar...@gmail.com>: >> Gensym produces symbols that are not eq to any other symbols created any >> other way. The bindings library produces symbols from strings, so they >> aren't eq to the gensym'd one. >> >> Jay >> >> Sent from my iPhone >> >> On 2011/07/31, at 15:13, J G Cho <g...@fundingmatters.com> wrote: >> >>> I am a bit puzzled by this error: >>> >>> >>> Exception >>> The application raised an exception with the message: >>> >>> extract-binding/single: 'q10493 not found in '((q10493 . "no")) >>> >>> >>> Context: >>> Symbol q10493 was generated by (gensym 'q) and used in >>> >>> (list (radio-input (symbol->string nom) "yes") >>> (radio-input (symbol->string nom) "no"))) >>> >>> When I try to extract it >>> >>> (define (extract-single nom) >>> (λ (bindings) >>> (extract-binding/single nom bindings))) >>> >>> it complains.... >>> >>> So I changed to >>> (define (extract-single nom) >>> (λ (bindings) >>> (extract-binding/single (string->symbol (symbol->string nom)) >>> bindings))) >>> >>> And it seems to work but left me scratching my head. >>> >>> Does anybody care to shed some light on this? >>> >>> jGc >>> >>> _________________________________________________ >>> For list-related administrative tasks: >>> http://lists.racket-lang.org/listinfo/users >> > -- Jay McCarthy <j...@cs.byu.edu> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
