Two clocks – Electric Clojure

electric-two-clocks.md

Two clocks – Electric Clojure

• demonstrates streaming lexical scope that crosses frontend/backend seamlessly

20230224.two.clocks.mp4

Code notes:

• server and client clocks s and c are defined in the same expression
• (- s c) shows local and remote values are consumed in the same expression
• Lexical bindings c and s are reactive values
• Clojure itself is made reactive by e/defn which compiles Clojure forms to DAGs
• everything is reactive, so it feels like nothing is reactive
• Lexical bindings like c can be thought of as either a flow and a value, both worldviews are valid, sometimes you need one sometimes the other
• the latency can skew negative because the client and server sampling rates are not synchronized. Note it doesn’t drift.

user.cljc

(ns user.demo-6-two-clocks
  #?(:cljs (:require-macros user.demo-6-two-clocks))
  (:require [hyperfiddle.electric :as e]
            [hyperfiddle.electric-dom2 :as dom]))

(e/defn App []
  (e/client
    (dom/h1 (dom/text "Two Clocks"))

    (let [c (e/client e/system-time-ms)
          s (e/server e/system-time-ms)]

      (dom/div (dom/text "client time: " c))
      (dom/div (dom/text "server time: " s))
      (dom/div (dom/text "latency: " (- s c))))))