Re: Programming clojure second Edition
I got it, Think you very much!
在 2014年2月4日星期二UTC+8上午2时01分50秒，Justin Smith写道：
>
> 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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>>
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Re: Programming clojure second Edition
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?
> > --
> > You received this message because you are subscribed to the Google
> > Groups "Clojure" group.
> > To post to this group, send email to clo...@googlegroups.com
> > Note that posts from new members are moderated - please be patient
> > with your first post.
> > To unsubscribe from this group, send email to
> > clojure+u...@googlegroups.com
> > For more options, visit this group at
> > http://groups.google.com/group/clojure?hl=en
> > ---
> > You received this message because you are subscribed to the Google
> > Groups "Clojure" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> > an email to clojure+u...@googlegroups.com .
> > For more options, visit https://groups.google.com/groups/opt_out.
>
>
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Re: Programming clojure second Edition
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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