I'm displaying a set of questions for a quiz test and I'm assigning a number to each question just to number them when they are shown in the browser:
(defn questions-list
[]
(let [counter (atom 0)]
(fn []
(into [:section]
(for [question @(re-frame/subscribe [:questions])]
[display-question (assoc question :counter (swap! counter inc))])))))
The problem is that when someone edits a question in the browser (and the dispatch is called and the "app-db" map is updated) the component is re-rendered but the atom "counter" logically starts from the last number not from zero. So I need to reset the atom but I don't know where. I tried with a let inside the anonymous function but that didn't work.
In this case I'd just remove the state entirely. I haven't tested this code, but your thinking imperatively here. The functional version of what your trying to do is something along the lines of: Poor but stateless:
(let [numbers (range 0 (count questions))
indexed (map #(assoc (nth questions %) :index %) questions)]
[:section
(for [question indexed]
[display-question question])])
but this is ugly, and nth is inefficient. So lets try one better. Turns out map can take more than one collection as it's argument.
(let [numbers (range 0 (count questions))
indexed (map (fn [idx question] (assoc question :index idx)) questions)]
[:section
(for [question indexed]
[display-question question])])
But even better, turns out there is a built in function for exactly this. What I'd actually write:
[:section
(doall
(map-indexed
(fn [idx question]
[display-question (assoc question :index idx)])
questions))]
Note: None of this code has actually been run, so you might have to tweak it a bit before it works. I'd recommend looking up all of the functions in ClojureDocs to make sure you understand what they do.