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While `length' gives you number of pairs in a list, it's also useful to
determine the number of pairs in a (potentially) improper list. Since
an efficient implementation of this procedure cannot be defined outside
the random-access library, I propose adding the following procedure.
Unless there are objections, I will add this to the next revision of the
procedure: (count obj) -> k
Returns the number of pairs in the chain of pairs, obj. When given a
list, this procedure returns a result equivalent to (length obj). This
operation must take time bounded by O(log k).
(count '(a b c)) => 3
(count '(a (b) (c))) => 3
(count '(a b . c)) => 2
(count '()) => 0
(count 5) => 0