Yes, the discussion about contains? has come up before, but there's a new
aspect to this particular instance of the discussion that most of the posts
seem to be ignoring.
The original poster specifically pointed out that his sequence was
constructed by calling the `keys` function on a map:
(keys {:a "f" :b 23})
He then went on to point out that it doesn't return just a regular,
ordinary lazy sequence, but some sort of special type called a "KeySeq".
The documentation says that `contains?` looks for whether a given "key" is
present. Probably when the documentation was written, there was some
assumption that by saying it looks for a "key", that makes it obvious it
only works on associative collections.
But look here, we've got a sequence of keys. We know it is comprised of
keys, and obviously Clojure knows it is a sequence just of keys (because of
the custom type). Therefore, it was reasonable for the poster to think
that `contains?` would work on to determine whether a given key was in the
collection -- it is a collection with keys!
So I think the new idea here, worthy of discussion, is this:
How can we reword the doc for `contains?` so that it clearly does not apply
to a sequence of keys?
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