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 like https://github.com/dakrone/cheshire or
https://github.com/clojure/data.json and 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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