minimal Klipse to-do list app in ClojureScript with Reagent

klipse-todo-mvp.cljs

;; Instructions:
;; 1. go to http://app.klipse.tech/?container=1
;; 2. Paste this entire gist into the upper left code window
;; 3. Wait 3 seconds for the code to evaluate - the to-do list app should appear in the upper right window
;; original program source: https://orgpad.com/o/BSZ05PGN1PMbIjmwIT3Vhs?s=clojure-tutorial
(require 
  '[reagent.core :as r]
  '[reagent.dom :as r-dom])

(defn todo-app []
  "Renders a list of all todos.
  Done todos are crossed.
  Deleted todos are hidden from display."
  (let [todos (r/atom 
                [{:text "Start Clojure tutorial" :id 0}
                 {:text "Finish Clojure tutorial" :id 1}
                 {:text "Create a video for it" :id 2}
                 {:text "Fix bugs in OrgPad" :id 3}])
                done-items (r/atom #{0})
        input-val (r/atom "")]
    (fn []
      (let [dummy1 @todos
            dummy2 @done-items]
      [:section {:style {:margin "0"}}
   [:span {:style {:font-weight 600}} "List of todos for today:"]
   [:ul
    (for [todo @todos]
      (when (not (:deleted todo))
      ^{:key (:id todo)}
      [:li (when (contains? @done-items (:id todo))
             {:style {:text-decoration "line-through"}}) 
       [:span {:style {:margin-right "0.25em"}} (:text todo)]
       (if (contains? @done-items (:id todo))
         [:button
          ;; TIL: How to remove items from a set in Clojure
          {:on-click #(swap! done-items disj (:id todo))
             :style {:padding "0.25em" 
                     :margin-bottom "0.5em"}} "↺"]
         [:button
            {:on-click #(swap! done-items conj (:id todo))
             :style {:padding "0.25em" 
                     :margin-bottom "0.5em"}} "✔"])
       [:button
            {:on-click #(swap! todos update-in [(:id todo) :deleted] nil?)
             :style {:padding "0.25em" 
                     :margin-bottom "0.5em"}} "×"]
       ]))]
   [:input {:type "text"
            :placeholder "Enter new item text here"
            :value @input-val
            :on-change #(reset! input-val (-> % .-target .-value))}]
   [:button 
    {:on-click #(let [new-todo {:text @input-val
                                :id (count @todos)}]
                     (swap! todos conj new-todo)
                     (reset! input-val ""))} "Add item"]
   ]))))

(r-dom/render [todo-app] js/klipse-container)

((todo-app))