using -> on a nested hash-map with string keywords.

[Boris V. Schmid]

Can someone tell me what I'm overlooking (clojure 1.4)

(-> (hash-map :b (hash-map :a 3)) :b :a)

3

user> (-> (hash-map "b" (hash-map :a 3)) "b" :a)

; Evaluation aborted: java.lang.String cannot be cast to clojure.lang.IFn

I'm not sure why the first can work, and the second cannot. Is it a logical limitation of the language, or an oversight in how the macro -> is build?

[Dave Ray]

Keywords implement IFn meaning they can act as functions that look
themselves up in a map. Strings are just strings. Replace "b" with
(get "b") and you'll get the behavior you're looking for.

Dave

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[Jay Fields]

(:b {:b 1}) => 1

("b" {"b" 1}) => same error.

If you want that to work, you need something that creates ({"b" 1} "b") or (get {"b" 1} "b")

for your example, I believe this works

(-> (hash-map "b" (hash-map :a 3)) (get "b") :a)

Cheers, Jay

[Alan Malloy]

Yes, but really to GET a value nested IN a series of maps, he should
just be using get-in, rather than threading anything at all.

On May 31, 7:59 am, Dave Ray <dave...@gmail.com> wrote:
> Keywords implement IFn meaning they can act as functions that look
> themselves up in a map. Strings are just strings. Replace "b" with
> (get "b") and you'll get the behavior you're looking for.
>
> Dave
>

[Dave Ray]

Too true.

[Boris V. Schmid]

Thanks, it was get-in that I was looking for, but couldn't find. Also thanks to Dave for explaining that keywords have some internal magic compared to strings. will remember!

> > clojure+unsubscribe@googlegroups.com

[Sean Corfield]

On Fri, Jun 1, 2012 at 12:08 AM, Boris V. Schmid <boris....@gmail.com> wrote:
> Thanks, it was get-in that I was looking for, but couldn't find.

At this point I'll give a plug for http://clojureatlas.com as a great
way to explore the Clojure core/libraries by concept.
--
Sean A Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/
World Singles, LLC. -- http://worldsingles.com/

"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)