Clojure Programming/TJP Examples

-> user=> (-> "hello" .toUpperCase (.replace "H" "J")) "JELLO" However -> works on everything user=> (-> true (if inc dec) (map [1 2 3])) (2 3 4) or expanded (map (if true inc dec) [1 2 3]) So one can also use macros and normal functions in ->, i.e. non-methods. accessor (def unit-test-name (accessor unit-test :name)) user=> (def e-str (struct employee "John" 123)) #'user/e-str user=> e-str {"name" "John", "id" 123} user=> ("name" e-str) ; FAIL: string not an accessor java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn at user.eval__2537.invoke(Unknown Source) at clojure.lang.Compiler.eval(Compiler.java:3847) at clojure.lang.Repl.main(Repl.java:75) user=> (def e-name (accessor employee "name")) ; bind accessor to e-name #'user/e-name user=> (e-name e-str) ; use accessor "John" binding (binding [*test-out* System/out] (run-tests)) butlast user=> (butlast "hello") (\h \e \l \l) concat (defn poly-expand poly-expand [points] (loop [aa (first points) remaining (rest points) built (empty points)] (if (empty? remaining) (concat built [aa (first points)]) (recur (first remaining) (rest remaining) (concat built [aa (first remaining)]))))) (poly-expand '[a b c d]) -> [a b b c c d d a] def (def *a* 10) defmulti defmethod (defmulti fib int) (defmethod fib 0 [_] 1) (defmethod fib 1 [_] 1) (defmethod fib :default [n] (+ (fib (- n 2)) (fib (- n 1)))) user=> (map fib (range 10)) (1 1 2 3 5 8 13 21 34 55) doto (doto (new java.util.HashMap) (put "a" 1) (put "b" 2)) -> {a=1, b=2} NB: doto returns the object after modification, which is very convenient. Consider in the above example no variable binding is required to access the resultant object. (.addChild *scene-graph* (doto (KeyNavigatorBehavior. (-> *universe* .getViewingPlatform .getViewPlatformTransform)) (setSchedulingBounds (BoundingSphere. (Point3d.) 10000.0)))) Here you can see it is much more readable using doto than the alternative which would be to create a temporary binding with let. interpose apply (defn factorial [n] (apply * (range 2 (inc n)))) reverse user=> (apply str (interpose " " (reverse (.split "I am cold" " ")))) "cold am I" into-array double-array user=> (into-array (map double-array [[1.0] [2.0]])) #<double[][] [[D@1fa1bb6> filter user=> (filter identity [1 2 nil false 4]) (1 2 4) loop ; compute the factorial of 5, establishes two 'variables' cnt and acc ; cnt is decremented every call until it reaches 0 ; acc stores the result of multiplying each value cnt took (loop [cnt 5 acc 1] (if (zero? cnt) acc (recur (dec cnt) (* acc cnt)))) lazy-cons (defn fib-seq [] ((fn rfib [a b] (lazy-cons a (rfib b (+ a b)))) 0 1)) user> (take 20 (fib-seq)) (0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181) fn (map (fn [a] (str "hi " a)) ["mum" "dad" "sister"]) ; => ("hi mum" "hi dad" "hi sister") "lambda" Use fn, or even better there is a custom syntax to create an anonymous function: (map #(println "hi" %) ["mum" "dad" "sister"]) Arguments in the body are determined by the presence of argument literals taking the form %, %n or %&. % is a synonym for %1, %n designates the nth arg (1-based), and %& designates a rest arg. map user=> (map + [1 2 3 4] [1 2 3 4]) (2 4 6 8) memfn (map (memfn charAt i) ["fred" "ethel" "lucy"] [1 2 3]) -> (\r \h \y) proxy (defn rev-vector-seq [v] (when (< 0 (count v)) (proxy [clojure.lang.ISeq] [] (seq [] this) (first [] (peek v)) (rest [] (rev-vector-seq (pop v)))))) (doto (javax.swing.JFrame.) (addKeyListener (proxy [java.awt.event.KeyListener] [] (keyPressed [e] (println (.getKeyChar e) " key pressed")) (keyReleased [e] (println (.getKeyChar e) " key released")) (keyTyped [e] (println (.getKeyChar e) " key typed")))) (setVisible true)) recur See loop ref ref-set user=> (def foo (ref 0)) #'user/foo user=> foo #<Ref clojure.lang.Ref@7c2479a4> user=> @foo 0 user=> (ref-set foo 1) java.lang.IllegalStateException: No transaction running (NO_SOURCE_FILE:0) user=> (dosync (ref-set foo 1)) 1 user=> @foo 1 "remainder" "%" "mod" rem user=> (rem 5 2) 1 remove The opposite of filter (remove nil? [1 2 nil 3 false 4 5]) -> (1 2 3 false 4 5) (remove #{2 4} [1 2 nil 3 false 4 5]) -> (1 nil 3 false 5) replace (replace {"ll" ""} "hello world") require (require '[clojure.zip :as zip]) assoc defstruct struct struct-map user=> (defstruct employee :name :id) #'user/employee user=> (struct employee "Mr. X" 10) {:name "Mr. X", :id 10} user=> (struct-map employee :id 20 :name "Mr. Y") {:name "Mr. Y", :id 20} user=> (def a (struct-map employee :id 20 :name "Mr. Y")) #'user/a user=> (def b (struct employee "Mr. X" 10)) #'user/b user=> (:name a) ; observe that :name is an accessor "Mr. Y" user=> (:id b) ; same with :id 10 user=> (b :id) 10 user=> (b :name) "Mr. X" user=> (assoc a :name "New Name") {:name "New Name", :id 20} user=> a ; note that 'a' is immutable and did not change {:name "Mr. Y", :id 20} user=> (def a1 (assoc a :name "Another New Name")) ; bind to a1 #'user/a1 user=> a1 {:name "Another New Name", :id 20} test user=> (defn #^{:test (fn [] (assert (= 4 (myadd 2 2))))} myadd [a b] (+ a b)) #'user/myadd user=> (test #'myadd) :ok zippers user=> (-> (zip/vector-zip [[1 2] 3 [[4 5] 7 8]]) zip/down zip/right zip/right zip/down zip/down zip/right (zip/edit inc) zip/root) [[1 2] 3 [[4 6] 7 8]]