Refactoring to Macros with Clojure

Refactoring to Macros with Clojure Dimitry Solovyov @dimituri

Let's talk about FUNCTIONAL PROGRAMMING

liftIO $ atomicModifyIORef sc $ n -‐> (n + 1, ()) d <-‐ f v >>: onInner liftIO $ ds `addDisposable` d

LISP in 3 minutes via @bodiltv

Clojure      It's a Lisp Compiled Dynamic types Type hints Macros

Clojure        It's a Lisp Compiled Dynamic types Type hints Macros Optional static types Optional Prolog

http://clojure.org/java_interop

HttpServer server = HttpServer.create(address, 0); server.createContext(path, handler); server.setExecutor(null); server.start();

HttpServer server = HttpServer.create(address, 0); server.createContext(path, handler); server.setExecutor(null); server.start(); (doto (HttpServer/create address 0) (.createContext path handler) (.setExecutor nil) (.start))

macro |ˈmakrəәʊ| noun ( pl. macros ) 1 (also macro instruction) Computing a single instruction that expands automatically into a set of instructions to perform a particular task.

(let* [G__360 (HttpServer/create address 0)] (.createContext G__360 path handler) (.setExecutor G__360 nil) (.start G__360) G__360) (doto (HttpServer/create address 0) (.createContext path handler) (.setExecutor nil) (.start))

.println(Encoding.encodeBase64(Encoding.decodeUrl(Encoding.decodeBas

String url = Encoding.decodeBase64(b); String decodedUrl = Encoding.decodeUrl(url); String encodedUrl = Encoding.encodeBase64(decodedUrl); System.out.println(encodedUrl);

String url = Encoding.decodeBase64(b); String decodedUrl = Encoding.decodeUrl(url); String encodedUrl = Encoding.encodeBase64(decodedUrl); System.out.println(encodedUrl); (-‐> b Encoding/decodeBase64 Encoding/decodeUrl Encoding/encodeBase64 println)

-‐> (-‐> stuff (foo ,,, a) (bar ,,, b c d) (baz ,,, e f))

-‐>>-‐> (-‐> stuff (foo ,,, a) (bar ,,, b c d) (baz ,,, e f)) (-‐>> stuff (foo a ,,,) (bar b c d ,,,) (baz e f ,,,))

-‐<>-‐>>-‐> (-‐> stuff (foo ,,, a) (bar ,,, b c d) (baz ,,, e f)) (-‐>> stuff (foo a ,,,) (bar b c d ,,,) (baz e f ,,,)) (-‐<> stuff (foo a <>) (bar b c <> d) (baz <> e f))

“Swiss Arrows” -‐<>> -‐?<> -‐!> -‐!>> -‐!<> <<-‐ -‐< -‐<:p -‐<< -‐<<:p -‐<>< -‐<><:p https://github.com/rplevy/swiss-arrows

Q: How do I get the result from a chain of computatoins that may fail?

PhoneNumber number = phoneMap.get(person); if (number != null) { Carrier carrier = carrierMap.get(number); if (carrier != null) { return addressMap.get(address); } } return null;

WHAT YOU'RE LOOKING FOR IS AN OPTION MONAD

PhoneNumber number = phoneMap.get(person); if (number != null) { Carrier carrier = carrierMap.get(number); if (carrier != null) { return addressMap.get(address); } } return null; (some-‐>> (.get phoneMap person) (.get carrierMap) (.get addressMap))

Clojure vectors implement java.lang.Comparable java.util.RandomAccess

All Clojure functions implement java.util.Comparator java.lang.Runnable java.util.concurrent.Callable

List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o2.compareTo(o1); } });

List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o2.compareTo(o1); } }); List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, (o1, o2) -‐> o2.compareTo(o1));

List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o2.compareTo(o1); } }); (doto (ArrayList. [1 3 4 8 2]) (Collections/sort (fn [o1 o2] (.compareTo o2 o1)))) List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, (o1, o2) -‐> o2.compareTo(o1));

List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o2.compareTo(o1); } }); (doto (ArrayList. [1 3 4 8 2]) (Collections/sort (fn [o1 o2] (.compareTo o2 o1)))) (sort #(compare %2 %1) [1 3 4 8 2]) List<Integer> numbers = Arrays.asList(1, 3, 4, 8, 2); Collections.sort(numbers, (o1, o2) -‐> o2.compareTo(o1));

(defn len-‐reflected [s] (.length s)) (defn len-‐hinted ^String [^String s] (.length s)) user=> (time (dotimes [i 1000000] (len-‐reflected (str i)))) "Elapsed time: 3204.913 msecs" nil user=> (time (dotimes [i 1000000] (len-‐hinted (str i)))) "Elapsed time: 113.317 msecs" nil

Polyglot projects with Leiningen (defproject clojure-‐java "1.0.0-‐SNAPSHOT" :description "Example Clojure+Java project." :min-‐lein-‐version "2.0.0" :source-‐paths ["src/clojure"] :java-‐source-‐paths ["src/java"] :javac-‐options ["-‐target" "1.5" "-‐source" "1.5"]) http://leiningen.org

http://www.ldn.lv Workshop: Clojure Saturday, May 18, 2013 10:00 am Citadeles iela 12, Riga http://riga.techhub.com/

(defmacro doto [x & forms] (let [gx (gensym)] `(let [~gx ~x] ~@(map (fn [f] (if (seq? f) `(~(first f) ~gx ~@(next f)) `(~f ~gx))) forms) ~gx)))

(ns foo.core (:gen-‐class)) (defn -‐main "I don't do a whole lot ... yet." [& args] (println "I'm a little pony")) foo$ lein run I'm a little pony

(defn make-‐example [] (proxy [Object] [] (toString [] "I'm a little pony"))) user=> (.toString (make-‐some-‐example)) "I'm a little pony"

class Example { void someMethod(String x) { someMethod(x, null) } void someMethod(String x, String y) { doSomethingWith(x, y); } } (proxy [Example] [] (toString ([x] (proxy-‐super someMethod x)) ([x y] (do-‐other-‐stuff this x y))))

(let [^LoadingCache cache (doto CacheBuilder/newBuilder (.maximumSize 1000) (.build (reify CacheLoader (load ^Graph [^Key key] (create-‐expensive-‐graph key)))))]) LoadingCache<Key, Graph> cache = CacheBuilder.newBuilder() .maximumSize(1000) .build(new CacheLoader<Key, Graph>() { public Graph load(Key key) { return createExpensiveGraph(key); } }); LoadingCache<Key, Graph> cache = CacheBuilder.newBuilder() .maximumSize(1000) .build((key) -‐> createExpensiveGraph(key));

Refactoring to Macros with Clojure

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