Define Function

Write a function which returns a personalized greeting. (= (__ “Dave”) “Hello, Dave!”)

Hello World

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(fn [name] (str "Hello, ", name, "!"))

or

“#(str "Hello, ” % “!”)"

Filter

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(filter #(> % 5) '(3 4 5 6 7))

returns ‘(6 7)

Local Bindings

Clojure lets you give local names to values using the special let-form.

Sample1

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(let [x 5] (+ 2 x))

In Java something like:

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int x = 5;
x + 2;

Sample2

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(let [x 3, y 10] (- y x))

In Java something like:

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int x = 3, y = 10;
y - x;

Recursion

A recursive function is a function which calls itself. This is one of the fundamental techniques used in functional programming.

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(defn recursionFn [x]
  (when (> x 0)
    (conj (recursionFn (dec x)) x)))

=>(recursion 5)
=>[5 4 3 2 1]

Rearranging Code “->” vs “->>”

These two lines are the same

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(sort (rest (reverse [2 5 4 1 3 6])))

(-> [2 5 4 1 3 6] (reverse) (rest) (sort))

I like this explaination:

;; let's compare thread first (->) and thread last ( ->> )
user=> (macroexpand '(-> 0 (+ 1) (+ 2) (+ 3)))
(+ (+ (+ 0 1) 2) 3)
user=> (macroexpand '(->> 0 (+ 1) (+ 2) (+ 3)))
(+ 3 (+ 2 (+ 1 0)))

Loop and recur

(loop [bindings] exprs)

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=>(loop [x 10]
  (when (> x 0)
      (if (> x 5)
          (print x)
          (print (* -1 x)))
      (recur (- x 1))))

=>-10-9-8-7-6-54321