member returns list (was: Re: To `boundp' or not to `boundp'?)

[Emanuel Berg]

Barry Margolin <barmar@alum.mit.edu> writes:

> ... MEMBER, which intuitively seems like it would
> just return a boolean, but actually returns the tail
> of the list where the element was found.

Yes, and I have wondered about that. Is it useful,
perhaps with the use of `car' (?) as in:

    (car (member 2 '(1 2 3))) ; 2
    (car (member 0 '(1 2 3))) ; nil

Or is it some "leftover optimization" thing where
`cdr' is faster than returning `t', and can be used
the same way?

Or is it something else?

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