Hi Pablo,
I think you're right. Have a look at flatten source
(defn flatten
"Takes any nested combination of sequential things (lists, vectors,
etc.) and returns their contents as a single, flat sequence.
(flatten nil) returns an empty sequence."
{:added "1.2"
:static true}
[x]
(filter (complement sequential?)
(rest (tree-seq sequential? seq x))))
it is the rest function that causes this behavior and it seems to be just
an optimization to avoid filtering the first element of tree-seq that is
known to be the whole sequence. A simpler definition of flatten seems to
have the behavior you expected.
(defn flatten1 [x] (filter (complement sequential?) (tree-seq sequential?
seq x)))
Il giorno mercoledì 1 luglio 2015 13:55:28 UTC+2, J. Pablo Fernández ha
scritto:
>
> Hello Clojurists,
>
> Today I was surprised by the result of (flatten 1) which is '(). I was
> expecting '(1) or an error. Talking in some other people in #clojure @
> clojurians.net, not everybody agrees that '(1) is a good result but that
> '() is somewhat surprising. Would it be better if it raised an error when
> the attribute is not sequential?
>
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