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Re: Proposal: count

This page is part of the web mail archives of SRFI 101 from before July 7th, 2015. The new archives for SRFI 101 contain all messages, not just those from before July 7th, 2015.

My only worry is that the name 'count' clashes with a traditional name
for a procedure that counts the number of elements of a collection
that satisfy some predicate (and could therefore be confusing, in
addition to causing actual name collisions).  I do not, however, have
a concrete suggestion for doing better.


On Sun, Sep 20, 2009 at 6:58 PM, David Van Horn <dvanhorn@xxxxxxxxxxx> wrote:
> 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
> David
> 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