if pred is false or nil (the two cases "when" would rule out), it would be
an error to apply it to an argument
#{\a \b} is a literal set syntax, containing keys \a and \b. {\a \b} is a
literal hash-map syntax, with one key \a mapped to the value \b. As far as
index-filter is concerned, it only selects \a, since that is the only key
you can match.
On Monday, February 3, 2014 7:57:55 AM UTC-8, Jim foo.bar wrote:
>
> a vector is a function of its indices
> a map is a function of its keys
> a set is a function of its elements
>
> does this help at all?
>
> Jim
>
>
>
> On 03/02/14 15:29, action wrote:
> > (defn index-filter [pred coll]
> > (when pred
> > (for [[idx elt] (indexed coll) :when (pred elt)] idx)))
> >
> > (index-filter #{\a \b} "abcdef")
> > -> (0 1)
> >
> > but I don't know why use "when pred" in the code,
> > and why "(index-filter {\a \b} "abcdef")" doesn't work?
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