Java with a Clojure mindset
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This document discusses functional programming concepts like pure functions, immutable data, and avoiding side effects and shared state, comparing them to object-oriented and imperative approaches. It shows examples of representing and transforming data as immutable Clojure data structures like vectors and maps. Functions for processing this data in a declarative way are demonstrated, with an emphasis on composability through chaining of pure functions.
![{:select [:id :client :amount]
:from [:transactions]
:where [:= :client "a"]}
apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave
interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all
partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take-
nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge
merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index](https://image.slidesharecdn.com/java-with-a-clojure-mindset-190224200006/85/Java-with-a-Clojure-mindset-77-320.jpg)
![[{:id 1 :client 32 :amount 3}
{:id 2 :client 87 :amount 7}
{:id 3 :client 32 :amount 4}
{:id 4 :client 40 :amount 6}]
apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave
interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all
partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take-
nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge
merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index](https://image.slidesharecdn.com/java-with-a-clojure-mindset-190224200006/85/Java-with-a-Clojure-mindset-78-320.jpg)
![[:html
[:body
[:p "Count: 4"]
[:p "Total: 20"]]]
apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave
interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all
partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take-
nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge
merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index](https://image.slidesharecdn.com/java-with-a-clojure-mindset-190224200006/85/Java-with-a-Clojure-mindset-79-320.jpg)
![{:id :string
:name :string
:deposits [{:id :string
:amount :int
:timestamp :long}]}
apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave
interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all
partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take-
nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge
merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index](https://image.slidesharecdn.com/java-with-a-clojure-mindset-190224200006/85/Java-with-a-Clojure-mindset-81-320.jpg)
Java with a Clojure mindset
- 1. Java, with a Clojure mindset @DanLebrero www.akvo.org
- 13. Give 10$ free cash if client makes 1000 bets in less than 1 week
- 15. Pure Functions
- 17. “Programmers are constantly in maintenance mode.” ― The Pragmatic Programmer
- 18. Side Effects
- 20. Side effects are the enemy
- 22. State
- 25. Atom Thread-1 Thread-2 fn2( ) = fn1( ) = ====fn2( ) = ==? ==? ==?
- 29. “Is this thread safe?” ― Every Java developer, every day.
- 30. 1. State is consistent 2. Function must be pure 3. Only safe within the pure function
- 31. public class ClientBonus { private final Client client; private final Bonus bonus; private final DepositList deposits; …
- 33. public interface ConcurrentMap<…> extends Map<…> { V compute(K key, BiFunction<…> remappingFunction) V computeIfAbsent(K key, Function<…> mappingFunction) V computeIfPresent(K key, BiFunction<…> remappingFunction) … }
- 34. public class TheStateHolder { private final Map<Long, ClientBonus> state = new ConcurrentHashMap<>(); public ClientBonus nextState(Long client, Bet bet) { return state.computeIfPresent( client, (k, currentState) -> currentState.nextState(bet)); }
- 35. public class ClientBonus { private final Client client; private final Bonus bonus; private final DepositList deposits; public ClientBonus nextState(Bet bet) { ... } …
- 36. Effects
- 38. public class ClientBonus { private final Client client; private final Bonus bonus; private final DepositList deposits; public ClientBonus nextState(Bet bet) { ... } …
- 39. public class ClientBonus { private final Client client; private final Bonus bonus; private final DepositList deposits; public Pair<ClientBonus,Effects> next(Bet bet) { ... } …
- 46. public interface Effect { void run(AllDependencies dependencies); }
- 47. Pair<ClientBonus, Effects> pair = theStateHolder.nextState(bet); pair.effects.run(dependencies);
- 48. Pair<ClientBonus, Effects> pair = theStateHolder.nextState(bet); pair.effects.run(dependencies); “Is this thread safe?”
- 49. Thread-1 Thread-2 Pair<> pair = theStateHolder.nextState(bet); Pair<> pair = theStateHolder.nextState(bet); pair.effects.run(dependencies); pair.effects.run(dependencies);
- 50. Pair<> pair = theStateHolder.nextState(bet); Pair<> pair = theStateHolder.nextState(bet); pair.effects.run(dependencies); pair.effects.run(dependencies); Thread-1 Thread-1 Thread-2 Thread-2
- 53. Can I pay?Can I pay? ACID Can I pay?
- 54. NoYes No
- 56. Co-Effects
- 60. public class KafkaConsumer { private AllDependencies allDependencies; private TheStateHolder theStateHolder; public void run() { while (!stop) { Bet bet = readNext(); Effects effects = theStateHolder.event(bet); effects.run(allDependencies); } } … }
- 61. public class KafkaConsumer { private AllDependencies allDependencies; private TheStateHolder theStateHolder; public void run() { while (!stop) { Bet bet = readNext(); Effects effects = theStateHolder.event(bet); effects.run(allDependencies); } } … }
- 62. public class KafkaConsumer { private AllDependencies allDependencies; private TheStateHolder theStateHolder; public void run() { while (!stop) { Bet bet = readNext(); Effects effects = theStateHolder.event(bet); effects.run(allDependencies); } } … }
- 63. public class KafkaConsumer { private AllDependencies allDependencies; private TheStateHolder theStateHolder; public void run() { while (!stop) { Bet bet = readNext(); Effects effects = theStateHolder.event(bet); effects.run(allDependencies); } } … }
- 64. public class KafkaConsumer { private AllDependencies allDependencies; private TheStateHolder theStateHolder; public void run() { while (!stop) { Bet bet = readNext(); Effects effects = theStateHolder.event(bet); effects.run(allDependencies); } } … }
- 65. •No getters •No locks or synch blocks •No try/catch •No logging •No mocks •No useless interfaces
- 68. Dynamic (vs Static) typing
- 69. clientBonus = Map.of( "client", Map.of("id", "123233"), "deposits", List.of( Map.of("amount", 3, "type", "CASH"), Map.of("amount", 234, "type", "CARD"))); ((List) clientBonus.get("deposits")) .stream() .collect( Collectors.summarizingInt( m -> (int) ((Map) m).get("amount")));
- 71. public class Bet { private String id; private int amount; private long timestamp; }
- 72. “It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.” ― Alan Perlis
- 73. {:type :bet :id "client1" :amount 23 :timestamp 123312321323}
- 74. apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index {:type :bet :id "client1" :amount 23 :timestamp 123312321323}
- 75. {:request-method :get :uri “/foobaz" :query-params {"somekey" “somevalue"} :headers {"accept-encoding" "gzip, deflate" "connection" "close"} :body nil :scheme :http :content-length 0 :server-port 8080 :server-name “localhost"} apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 76. {:status 200 :headers {"Content-Type" "text/html"} :body "Hello World"}} apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 77. {:select [:id :client :amount] :from [:transactions] :where [:= :client "a"]} apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 78. [{:id 1 :client 32 :amount 3} {:id 2 :client 87 :amount 7} {:id 3 :client 32 :amount 4} {:id 4 :client 40 :amount 6}] apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 79. [:html [:body [:p "Count: 4"] [:p "Total: 20"]]] apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 80. {:web-server {:listen 8080} :db-config {:host "xxxx" :user "xxxx" :password "xxxx"} :http-defaults {:connection-timeout 10000 :request-timeout 10000 :max-connections 2000} :user-service {:url “http://user-service” :connection-timeout 1000}} apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 81. {:id :string :name :string :deposits [{:id :string :amount :int :timestamp :long}]} apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 82. •Business logic •Infrastructure code •Configuration •Reflection/Metadata apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 84. REPL
- 86. Lisp (vs Fortan)
- 91. .filter(removeCsvHeaders(firstHeader)) .map(splitCsvString()) .map(convertCsvToMap(csvHeaders)) .map(convertToJson(eventCreator)) (filter not-header?) (map parse-csv-line) (map (partial zipmap headers)) (map ->event) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 87 65 9 10 - 40%!!
- 93. List.of( new Symbol("defn"), new Symbol("plus-one"), List.of( new Symbol("a"), new Symbol("b")), Map.of( new Keyword("time"), List.of(new Symbol("System/currentTimeMillis")), new Keyword("result"), List.of( new Symbol("+"), new Symbol("a"), new Symbol("b"), new Long(1))));
- 94. List.of( new Symbol("defn"), new Symbol("plus-one"), List.of( new Symbol("a"), new Symbol("b")), Map.of( new Keyword("time"), List.of(new Symbol("System/currentTimeMillis")), new Keyword("result"), List.of( new Symbol("+"), new Symbol("a"), new Symbol("b"), new Long(1)))); apply butlast concat cons count cycle diff distinct distinct? drop drop-last drop-while empty empty? every? ffirst filter first flatten fnext for frequencies group-by interleave interpose into into-array keep keep-indexed last lazy-cat map map-indexed mapcat next nfirst nnext not-any? not-empty not-every? nth nthnext partition partition-all partition-by pmap postwalk prewalk rand-nth reduce reductions remove replace rest reverse second seq? seque set shuffle some sort sort-by split-at split-with take take- nth take-while to-array-2d vec walk when-first assoc pop subvec replace conj rseq update-in update get get-in contains? find keys vals assoc assoc-in dissoc merge merge-with select-keys update-in update rename-keys map-invert reduce-kv dissoc-in disj join select project union difference intersection index
- 95. Summary
- 100. “A language that doesn’t affect the way you think about programming, is not worth knowing.” ― Alan Perlis
- 106. Come to ClojureCooomeeeee…Clojure is your friendClojure is happinessClojure is beauty