akar-london-clojurians.clj

(ns akar.talk-examples
  (:require [akar.try-out :refer :all]
            [clojure.xml :as xml])
  (:import [java.util.concurrent ConcurrentHashMap]
           [java.io ByteArrayInputStream]))

; Example 1

(def request-ids-pattern
  #"rid=(.*)\|(.*)")

(defn request-ids [headers]
  (let [request-ids-header (get headers "X-ABC-REQUEST-IDS")
        [main correlation] (some->> request-ids-header (re-seq request-ids-pattern) first rest)]
    {:main        main
     :correlation correlation}))

(request-ids {"X-ABC-REQUEST-IDS" "rid=2|3"})

; Example 2

(def cache
  (ConcurrentHashMap.))

(defn respond-to-event [event]
  (case (:evt-type event)
    (:child-added :child-updated) (.put cache (:path event) (:data event))
    :child-removed (.remove cache (:path event) (:data event))
    nil))

(respond-to-event {:evt-type :child-added :path "a" :data 11})

; Example 3

(defn record-http-call-metrics [status-code]
  (cond
    (< 199 status-code 300) (println :ok)
    (< 299 status-code 400) (println :xxx)
    (< 399 status-code) (println :error)))

; Example 4

(defn seqsum [xs]
  (if (empty? xs)
    0
    (+ (first xs)
       (seqsum (rest xs)))))

; Example 5

(defn finden [xs pred]
  (if (empty? xs)
    nil
    (let [x (first xs)]
      (if (pred x)
        x
        (find (rest xs) pred)))))

; Example 6

; https://github.com/clojure/clojure/blob/clojure-1.7.0/src/clj/clojure/core.clj#L2940

; Example 7

; http://gettingclojure.wikidot.com/cookbook:xml-html

(def xml-doc
  (xml/parse (ByteArrayInputStream. (.getBytes
    "<?xml version=\"1.0\"?>
      <calendar>
      <holiday type=\"International\">
      <name>International Lefthanders Day</name>
      <date>
      <month>August</month>
      <day>13</day>
      </date>
      </holiday>
      <holiday type=\"Personal\">
      <name>Rover's birthday</name>
      <date>
      <month>October</month>
      <day>12</day>
      </date>
      </holiday>
      <holiday type=\"National\">
      <name>Groundhog Day</name>
      <date>
      <month>February</month>
      <day>2</day>
      </date>
      </holiday>
      <holiday type=\"State\">
      <name>Kamehameha Day</name>
      <date>
      <month>June</month>
      <day>11</day>
      </date>
      </holiday>
      </calendar>"))))

(defn holiday-name [holiday]
  (first (:content (first (:content holiday)))))

(defn holiday-month [holiday]
  (first (:content (first (:content (second (:content holiday)))))))

(defn holiday-day [holiday]
  (first (:content (second (:content (second (:content holiday)))))))

(defn holiday-info [doc]
  (for [elt (xml-seq doc) :when (= :holiday (:tag elt))]
    [(holiday-name elt) (holiday-month elt) (holiday-day elt)]))