I believe the flatten in contrib is defined as follows. I can't
remember which module I found it in.
(defn flatten
"Takes any nested combination of sequential things (lists, vectors,
etc.) and returns their contents as a single, flat sequence.
(flatten nil) returns nil."
[x]
(filter (complement sequential?)
(rest (tree-seq sequential? seq x))))
-Travis
On Sep 2, 3:33 pm, Krukow <karl.kru...@gmail.com> wrote:
> Hello,
> At some point I needed at "flatten" function taking a list of atomic
> elements or nested lists, and producting a "flat" list of only atomic
> elements (in the same order). It should be lazy.
>
> This is what I came up with. Can anyone see a more elegant solution (I
> feel I am working "low-level" somehow).
>
> user> (defn flatten [lst]
> (lazy-seq
> (if (empty? lst) lst
> (let [[x & xs] lst]
> (if (list? x)
> (concat (flatten x) (flatten xs))
> (cons x (flatten xs)))))))
> #'user/flatten
> user> (flatten '(1 2 3 4))
> (1 2 3 4)
> user> (flatten '((1 2) (3) 4))
> (1 2 3 4)
> user> (flatten '(((1) 2) (3) 4))
> (1 2 3 4)
> user>
>
> /Karl
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