I can't answer for the author, but the answer you gave would be a good
sufficient reason to call seq in those places, yes?
If you create a function zipmap2 that is identical to zipmap, except it
does not have any calls to seq, you get these results:
user=> (zipmap [] [1])
{}
user=> (zipmap2 [] [1])
{nil 1}
I definitely think the former result makes more sense than the latter does.
If you are thinking that it would be better to have the calls to seq in the
if condition, that would be at least a little bit slower than the current
implementation, as it would have 2 additional calls to seq for every
iteration through the loop.
Andy
On Tue, Nov 29, 2016 at 7:42 PM, larry google groups <
lawrencecloj...@gmail.com> wrote:
> I apologize for this question, because I think it has been asked before,
> and yet I can not find the answer.
>
> In the definition of zipmap, what do these 2 lines do?
>
> ks (seq keys)
> vs (seq vals)
>
> In particular, what is (seq) doing? Is this to ensure that ks is false if
> "keys" is empty? And vs is false if "vals" is empty? Because an empty list
> (or vector) is truthy but we want it to be falsey in this situation?
>
> Is there any other reason to use (seq), other than to set the
> truthy/falsey values of ks and vs?
>
>
> (defn zipmap
> "Returns a map with the keys mapped to the corresponding vals."
> {:added "1.0"
> :static true}
> [keys vals]
> (loop [map {}
> ks (seq keys)
> vs (seq vals)]
> (if (and ks vs)
> (recur (assoc map (first ks) (first vs))
> (next ks)
> (next vs))
> map)))
>
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