Your first pointer says: 'THE constant #<undefined> ...' Does the particle 'The' not imply that letrec always uses the same (eq?) constant for initialization?
-----Original Message----- From: users-boun...@racket-lang.org [mailto:users-boun...@racket-lang.org] On Behalf Of Danny Yoo Sent: lunes, 05 de septiembre de 2011 21:09 To: Shriram Krishnamurthi Cc: users@racket-lang.org Subject: Re: [racket] recognizing undefined; shared in TR On Mon, Sep 5, 2011 at 2:18 PM, Shriram Krishnamurthi <s...@cs.brown.edu> wrote: > On Sat, Sep 3, 2011 at 11:17 PM, Shriram Krishnamurthi <s...@cs.brown.edu> wrote: >> Is there a way of checking whether a value position is undefined? >> Specifically, I'm trying to recognize the undefined value put in >> structures by SHARED. It appears that a undefined value is sometimes >> EQ? to another one, but this doesn't seem to be specified in the >> documentation (ie, that there is only one undefined value). > > Anyone have any thoughts on this? Is it okay to use EQ? According to: http://docs.racket-lang.org/reference/void.html we know the value of undefined is a constant, but there's no guarantee that they're the same value. However, I'm certain that undefined is a singleton value, from the implementation details in: http://docs.racket-lang.org/inside/im_values_types.html#(idx._(gentag._143._ (lib._scribblings/inside/inside..scrbl))) _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
