Clojure 基礎

if

(defn if-sample
  ""
  []
  (if true
    (str "this is true")
    (str "tihs is false")))
(if-sample)

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そこで出てきた実装をうまくなにかに生かす

yyyyMMddHHmm の形式の数字列を java.time.LocalDatetime 型にする

• 数字列からDatetime形式にしてよしなに取り扱いたい要件があった

• clj-time には clj-time.format の parse, unparse formatter を定義してできたが、java-time に切り替えたら parse がができなさそう

  (ns tmp
    (:require [clj-time.core :as t]
              [clj-time.local :as l]
              [clj-time.format :as f]
              [clj-time.predicates :as pr]
              [clojure.string :as str]
              [java-time :as time])
    (:import [java.time LocalDateTime]
             [java.time.format DateTimeFormatter]))
  
  (def custom-formatter (f/formatter "yyyyMMddHHmm"))
  (f/unparse custom-formatter (t/now))
  (f/parse custom-formatter "202105251003")
  

• 自作で作ってみたけどこれはどうなのか….

  (defn datetime-parser
    "yyyyMMddHHmm to java.time.localDatetime"
    [s]
    (let [tmp (->>
               (str/split (str s) #"")
               (partition 4))
          yyyy (->>
                (first tmp)
                (str/join))
          mm (->>
              (second tmp)
              (partition 2)
              (first)
              (str/join))
          dd (->>
              (second tmp)
              (partition 2)
              (second)
              (str/join))
          h (->>
             (last tmp)
             (partition 2)
             (first)
             (str/join))
          m (->>
             (last tmp)
             (partition 2)
             (second)
             (str/join))]
      (time/local-date-time (Integer. yyyy) (Integer. mm)
                            (Integer. dd) (Integer. h)
                            (Integer. m))))
  
  (datetime-parser 202106271918)
  ;; => #object[java.time.LocalDateTime 0xe6abc87 2021-06-27T19:18]