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Re: Reintroducing old `defined?'

Keith Wright <kwright@tiac.net> writes:

> >                                                     Ok "undefine" is
> >    not yet standardized either, but should be considered being
> >    standardized in the scheme standard as well, as non essential.

Does r5rs mention `undefine' at all?  I don't like undefine because
it is hard to implement:

(define (b) (display a))
(define a 12)
(b)                        -> 12

(undefine a)
a                          -> ERROR
(b)                        -> value "undefined"
                              ^^^^^^^^^^^^^^^^^ WRONG!


So I think it would be better to drop `undefine' completely.  



> DEFINED?

Doesn't `(environment-bound? (car (the-environment)) <sym>)' do what you
want?  (See Jim Blandy's environment proposal).


Jost