On Monday 15 December 2008 07:22, Stuart Sierra wrote:
> On Dec 15, 9:08 am, Randall R Schulz <[email protected]> wrote:
> > > flatten returns a sequence - in this case a sequence containing
> > > 'nil. How else would you flatten on nil?
> >
> > I would expect (flatten nil) => nil
>
> I agree, it's a bug, but I'm not sure how to fix it, unless it's just
> a special case that needs an "if".
If my current experience is any indicator (I'll leave it to you to
evaluate the "if" part of that), there will be a proliferation of these
tests at the point of calling of flatten if it's not done that one time
within it.
> Here's flatten, as written by
> Rich:
>
> (defn flatten [x]
> (let [s? #(instance? clojure.lang.Sequential %)]
> (filter (complement s?) (tree-seq s? seq x))))
>
> Which I think can now be simplified to:
>
> (defn flatten2 [x] (filter (complement coll?) (tree-seq coll? seq
> x)))
>
> Should maps be flattened in addition to "sequential things"?
My intuition is "no," but that's a pretty shallow intuition at this
point.
> But still (flatten2 nil) => (nil)
> In general, you get weird results if the thing passed to flatten is
> not a vector or a list:
>
> (flatten "hello") => ("hello" \h \e \l \l \o)
> (flatten2 "hello") => ("hello" \h \e \l \l \o)
>
> -Stuart Sierra
Randall Schulz
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