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Re: eval'ing a self-referential vector


Jim Blandy <jimb@red-bean.com> writes:

> > A vector is a valid expression even if it is cyclic.
> > 
> > It is well-specified how to handle it: a vector is self-evaluating.
> > 
> > So, I'd say that we have to be able to handle it.
> 
> Hmm, I'm not sure I agree.  I think you're taking the correspondence
> between Scheme data and expressions farther than R5RS does.
> 
> The set of valid Scheme expressions is defined in terms of a
> context-free grammar, without reference to the structures one can
> construct.  The definition is strictly textual, just like that of most
> other languages.
> 
> Since there is no string which corresponds to a cyclic structure, I'd
> say cyclic structures can't be valid expressions.

You're of course right---silly me.

/mdj