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Lesson 15 has been added
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‎otus-15/project.clj

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(defproject otus-15 "0.1.0-SNAPSHOT"
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:description "FIXME: write description"
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:url "http://example.com/FIXME"
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:license {:name "EPL-2.0 OR GPL-2.0-or-later WITH Classpath-exception-2.0"
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:url "https://www.eclipse.org/legal/epl-2.0/"}
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:dependencies [[org.clojure/clojure "1.11.1"]]
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:main ^:skip-aot otus-15.atom-watcher-validator
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:target-path "target/%s"
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:profiles {:uberjar {:aot :all
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:jvm-opts ["-Dclojure.compiler.direct-linking=true"]}})

‎otus-15/src/otus_15/atom_watcher_validator.clj

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(ns otus-15.atom-watcher-validator
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(:gen-class))
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;;
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;; Атомы
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;;
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(def oleg
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(atom {:name "Oleg"
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:age 25
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:wears-glasses? false}))
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; => #'user/oleg
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@oleg
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(swap! oleg #(update % :age + 3))
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; => {:age 28, :wears-glasses? false, :name "Oleg"}
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(swap! oleg update :age + 3)
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; => {:age 31, :wears-glasses? false, :name "Oleg"}
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@oleg
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(reset! oleg {:name "Nikita"})
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; => {:name "Nikita"}
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(def resources-by-user
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(atom {1005 {:cpu 35
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:store 63466734
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:memory 10442856
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:pids #{6266, 5426, 6542}}}))
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(swap! resources-by-user update-in [1005 :pids] conj 9999)
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@resources-by-user
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(deref resources-by-user)
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(comment
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;; Альтернативные варианты записи:
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;; 1)
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(fn [atom-value]
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(update-in atom-value [1005 :pids] conj 9999))
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;; 2)
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(fn [atom-value]
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(let [pids (get-in atom-value [1005 :pids])
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new-pids (conj pids 9999)
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new-atom-avalue (assoc-in atom-value [1005 :pids] new-pids)]
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new-atom-avalue))
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)
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;; Семантика «сравнить и изменить» и повторы
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(def accumulator
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(atom 0))
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(defn +slow
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[a b timeout]
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(println (format "current: %s, delta: %s, timeout: %s" a b timeout))
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(Thread/sleep timeout)
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(+ a b))
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(defn retry-example
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[]
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(future (swap! accumulator +slow 1 2000))
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(future (swap! accumulator +slow 2 5000)))
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(retry-example)
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@accumulator
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(comment
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"current: 0, delta: 1, timeout: 2000"
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"current: 0, delta: 2, timeout: 5000"
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;; -> #<Future@257a94bc: :pending>
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"current: 1, delta: 2, timeout: 5000"
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)
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;;
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;; Применение атомов для сохранения результата функции
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;;
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;; Замыкание атома внутри анонимной функции.
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(defn memoize
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[f]
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(let [mem (atom {})]
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(fn [& args]
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(if-let [e (find @mem args)]
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(val e)
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(let [ret (apply f args)]
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(swap! mem assoc args ret)
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ret)))))
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(def +mem (memoize +slow))
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(time (+mem 1 2 2000))
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;; => Elapsed time: 2001.006041 msecs
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(time (+mem 1 2 2000))
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;; => Elapsed time: 0.124338 msecs
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;;
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;; Функции-наблюдатели
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;;
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;; На момент вызова наблюдателя значение в ref'е уже может быть изменено.
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;; Необходимо опираться на аргументы old и new.
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(defn echo-watch
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[key ref old new]
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(println key ref old "=>" new))
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(add-watch accumulator :echo echo-watch)
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;; В наблюдателя передаётся только конечный результат вызова reset!/swap!.
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;; Перезапуски будут проигноированы, т.к. их результат отбрасывается.
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(retry-example)
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;; Наблюдатель вызвается даже если в результате вызовов
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;; reset!/swap! значение в атоме не было изменено.
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(reset! accumulator @accumulator)
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(defn echo-watch*
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[key ref old new]
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(when (not= old new)
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(println key ref old "=>" new)))
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;; Заменяю наблюдателя, зарегистрированного под ключом :echo.
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(add-watch accumulator :echo echo-watch*)
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(reset! accumulator @accumulator)
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;; Удаляю наблюдателя с ключом :echo.
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(remove-watch accumulator :echo)
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(reset! accumulator (inc @accumulator))
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;; Пример логирования при помощи наблюдателей.
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(defn log->file
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[filename _ref old new]
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(when (not= old new)
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(spit filename (str new \newline) :append true)))
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(def nikita
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(atom {:name "Nikita", :age 23}))
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;; Наблюдатель, принимающий аргумент через ключ.
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(add-watch nikita "program.log" log->file)
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(swap! nikita #(update % :age inc))
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(swap! nikita update :age inc)
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(swap! nikita identity)
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(swap! nikita assoc :wears-glasses? true)
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(swap! nikita update :age inc)
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(def history
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(atom ()))
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(defn log->atom
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[dest-atom key ref old new]
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nil)
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;; Наблююатель - частично применённая функция.
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(add-watch nikita :record (partial log->atom history))
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(swap! nikita update :age inc)
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(swap! nikita update :age inc)
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@history
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;;
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;; Функции-валидаторы
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;;
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(def acc
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(atom 0 :validator nat-int?))
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;; => #'user/acc
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(swap! acc dec)
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;; => IllegalStateException
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;; Ссылка может иметь только один валидатор.
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;; Установка нового валидатора подменяет исходный.
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(set-validator! acc int?)
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;; => nil
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(swap! acc dec)
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;; => -1
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(set-validator! acc (fn [x]
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(or (int? x)
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(throw (IllegalArgumentException.)))))
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;; => nil
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(reset! acc "string")
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;; => IllegalArgumentException
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(set-validator! acc nil)
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;; => nil
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(reset! acc "string")
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;; => "string"

‎otus-15/src/otus_15/future.clj

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(ns otus-15.future)
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;;
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;; Механизм future.
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;;
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(def long-calculation
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(future
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(Thread/sleep 5000)
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:done!))
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;; Получение значения с таймаутом.
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(deref long-calculation 1000 :impatient!)
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;; Получение значения.
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(deref long-calculation)
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;; Получение значения путём применения синтаксического сахара.
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@long-calculation
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;; Возвращает true, если значение было вычислено для future,
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;; promise, delay или ленивой последовательности.
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(realized? long-calculation)
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;; Футуры запоминают свои значения, таким образом после их
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;; однократного вычисления, они не будут перезапускаться.

‎otus-15/src/otus_15/ref.clj

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(ns otus-15.ref)
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(defn character
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[name & {:as opts}]
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(ref (merge {:name name
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:items #{}
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:health 500}
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opts)))
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(def smaug
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(character "Smaug"
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:health 500
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:strength 400
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:items (set (range 50))))
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(def bilbo
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(character "Bilbo"
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:health 100
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:strength 100))
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(def gandalf
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(character "Gandalf"
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:health 75
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:mana 750))
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(defn loot
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[from to]
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(dosync
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(when-let [item (-> @from :items first)]
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(alter to update :items conj item)
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(alter from update :items disj item))))
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(do
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(future (while (loot smaug bilbo)))
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(future (while (loot smaug gandalf))))
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@smaug
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@bilbo
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@gandalf
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[(-> @bilbo :items count) (-> @gandalf :items count)]
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(filter (:items @bilbo) (:items @gandalf))
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(defn flawed-loot
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[from to]
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(dosync
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(when-let [item (-> @from :items first)]
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(commute to update :items conj item)
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(commute from update :items disj item))))
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(do
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(future (while (flawed-loot smaug bilbo)))
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(future (while (flawed-loot smaug gandalf))))
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[(-> @bilbo :items count) (-> @gandalf :items count)]
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(filter (:items @bilbo) (:items @gandalf))
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(defn fixed-loot
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[from to]
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(dosync
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(when-let [item (-> @from :items first)]
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(commute to update :items conj item)
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(alter from update :items disj item))))
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(do
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(future (while (fixed-loot smaug bilbo)))
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(future (while (fixed-loot smaug gandalf))))
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[(-> @bilbo :items count) (-> @gandalf :items count)]
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(filter (:items @bilbo) (:items @gandalf))
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(defn attack
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[aggressor target]
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(dosync
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(let [damage (* (rand 0.1)
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(:strength @aggressor))]
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(commute target update :health (fn [target-health]
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(max 0 (- target-health damage)))))))
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(def alive? (comp pos? :health))
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(defn play
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[character action target]
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(while (and (alive? @character)
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(alive? @target)
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(action character target))
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(Thread/sleep (rand-int 50))))
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(do (future (play bilbo attack smaug))
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(future (play smaug attack bilbo)))
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[(:health @smaug) (:health @bilbo)]
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(def daylight (ref 1))
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(defn attack-with-light
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[aggressor target]
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(dosync
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(let [damage (* (rand 0.1)
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(:strength @aggressor)
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@daylight)]
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(commute target update :health (fn [target-health]
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(max 0 (- target-health damage)))))))
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(do (future (play bilbo attack-with-light smaug))
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(future (play smaug attack-with-light bilbo)))
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[(:health @smaug) (:health @bilbo)]
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(defn attack-with-light*
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[aggressor target]
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(dosync
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(let [damage (* (rand 0.1)
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(:strength @aggressor)
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(ensure daylight))]
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(commute target update :health (fn [target-health]
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(max 0 (- target-health damage)))))))

‎otus-15/src/otus_15/ref_task.clj

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(ns otus-15.ref-task)
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(def bilbo
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(ref {:name "Bilbo", :health 100, :strength 100}))
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(def smaug
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(ref {:name "Smaug", :health 500, :strength 400}))
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(def gandalf
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(ref {:name "Gandalf", :health 75, :mana 750}))
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(defn heal
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[healer target]
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(dosync (let [health-delta (* (rand 0.1) (:mana @healer))
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mana-delta (max 5 (/ health-delta 5))]
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(when (pos? health-delta)
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(alter healer update :mana - mana-delta)
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(commute target update :health + health-delta)))))
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(do (future (while (heal gandalf bilbo)
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(Thread/sleep (rand-int 50))))
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(future (while (heal gandalf smaug)
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(Thread/sleep (rand-int 50)))))
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[(:mana @gandalf) (:health @bilbo) (:health @smaug)]

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