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 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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