> I'm just a
> bit amazed that you would go away and write clojure code to consume JSON
> and all that, without realising that data-structures in Clojure are
> immutable!
That part is obvious enough, but I thought the new data structures
returned from assoc were being handed to map which then, in turn,
returned a new data structure where all values had been updated with
the values from assoc. But clearly, I got the syntax badly wrong.
On Sep 27, 2:21 pm, "Jim - FooBar();" <jimpil1...@gmail.com> wrote:
> the 2 previous responses answered your question perfectly ...I'm just a
> bit amazed that you would go away and write clojure code to consume JSON
> and all that, without realising that data-structures in Clojure are
> immutable! I think we can all agree they are *the* cornerstone of
> Clojure. It is a bit alien at first but it does pay off in the long
> run... If you absolutely need to stick with your code style (mutability
> not-recommended in general) use a java HashMap instead...
>
> Jim
>
> ps: i recently used a cheshire without any problems :-)
>
> On 27/09/12 18:53, gaz jones wrote:
>
>
>
>
>
>
>
> > Couple of initial things, Clojure has immutable data structures so
> > when you call for example 'assoc' it will return you a new map with
> > the new values assoc'd. It will not mutate the original, so:
>
> > (let [foo {}]
> > (assoc foo :a 1)
> > (assoc foo :b 2)
> > foo)
>
> > Will return {}. You need to do something like:
>
> > (-> {}
> > (assoc :a 1)
> > (assoc :b 2))
>
> > => {:a 1 :b 2}
>
> > FYI, assoc takes multiple kvps:
>
> > (assoc {} :a 1 :b 2)
>
> > Also, to return valid JSON, you cannot simply call 'str' on the map.
> > You need to use a library likehttps://github.com/dakrone/cheshireor
> >https://github.com/clojure/data.jsonand encode the map as JSON.
>
> > Perhaps you could illustrate the data structure you are holding inside
> > of @registry, and the structure of the JSON you would like to emit.
> > Laziness is not an issue here.
>
> > On Thu, Sep 27, 2012 at 12:02 PM, larry google groups
> > <lawrencecloj...@gmail.com> wrote:
> >> I would like 2 types of advice:
>
> >> 1.) an answer to this specific question
>
> >> 2.) advice on how one is suppose to debug mysteries likes this
>
> >> I have a simple web app that serves some data (hopefully in JSON
> >> format, but at the moment I will accept anything at all). The app uses
> >> Ring and Moustache and outputs the data.
>
> >> We start with a simple atom:
>
> >> (def registry (atom {}))
>
> >> We put some data in this atom. And then we output it. But I have had
> >> great difficulty getting anything to appear on the screen. Assuming
> >> the problem was with the fact the main sequence was lazy, I added in
> >> doall everywhere it made sense. But I still can not get anything to
> >> work:
>
> >> (defn current-users [request]
> >> "The default action of this app. Add new users to the registry, and
> >> delete the ones that are more than 15 seconds old"
> >> (let [this-users-params (:params request)
> >> final-map-for-output {}]
> >> (add-to-logged-in-registry this-users-params)
> >> (remove-old-registrants)
> >> (response (apply str (into {}
> >> (doall
> >> (map (fn [each-user-map]
> >> (doall
> >> (let [inner-details (second each-
> >> user-map)]
> >> (assoc final-map-for-output
> >> "username" (get inner-details "username" "nothing found for user"))
> >> (assoc final-map-for-output
> >> "updated" (get inner-details "updated" "nothing found for updated"))
> >> final-map-for-output)))
> >> @registry)))))))
>
> >> The various variations I have tried on this have either given me a
> >> blank white page or:
>
> >> {}
>
> >> Nothing else.
>
> >> I used to do simply:
>
> >> (response (apply str (doall @registry)))))
>
> >> This worked fine. But it did not output valid JSON, so I wanted to
> >> change the format. But I have not been able to get anything to appear
> >> on screen.
>
> >> Suggestions?
>
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