The keys docstring says it returns a sequence, and that's all you get:
it'll do first and next, nothing special about it. The contains? docstring
says it won't do a linear search, so that rules out the result of keys.
(KeySeq just wraps a seq of entries to return the key field.)
What's confusing to me here is that coll? will return true on a sequence.
On Wednesday, August 7, 2013 9:15:54 AM UTC-7, puzzler wrote:
>
> 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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