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undefine (Re: Reintroducing old `defined?')

Jost Boekemeier <jostobfe@calvados.zrz.TU-Berlin.DE> writes:

> 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!

This should be considered a bug.

It should be fixed when we have the new module system.
(Use unmemoization.)

/mdj