clojure.core

Introduction#

This document gives various basic functionalities offered by clojure. There is no explicit dependency needed for this and comes as a part of org.clojure.

Defining functions in clojure

(defn x [a b] 
        (* a b)) ;; public function

=> (x 3 2) ;; 6
=> (x 0 9) ;; 0

(defn- y [a b] 
        (+ a b)) ;; private function

=> (x (y 1 2) (y 2 3)) ;; 15

Assoc - updating map/vector values in clojure

When applied on a map, returns a new map with new or updated key val pairs.

It can be used to add new information in existing map.

(def userData {:name "Bob" :userID 2 :country "US"})
(assoc userData :age 27)            ;; { :name "Bob" :userID 2 :country "US" :age 27}

It replaces old information value if existing key is supplied.

(assoc userData :name "Fred")       ;; { :name "Fred" :userID 2 :country "US" } 
(assoc userData :userID 3 :age 27)  ;; {:name "Bob" :userID 3 :country "US" :age 27}

It can also be used on a vector for replacing value at the specified index.

(assoc [3 5 6 7] 2 10)              ;; [3 5 10 7]
(assoc [1 2 3 4] 6 6)               ;; java.lang.IndexOutOfBoundsException

Comparison Operators in Clojure

Comparisons are functions in clojure. What that means in (2>1) is (> 2 1) in clojure. Here are all the comparison operators in clojure.

Greater Than

(> 2 1) ;; true
(> 1 2) ;; false

Less Than

(< 2 1) ;; false

Greater Than or Equal To

(>= 2 1) ;; true
(>= 2 2) ;; true
(>= 1 2) ;; false

Less Than or Equal To

(<= 2 1) ;; false
(<= 2 2) ;; true
(<= 1 2) ;; true

Equal To

(= 2 2) ;; true
(= 2 10) ;; false

Not Equal To

(not= 2 2) ;; false
(not= 2 10) ;; true

Dissoc - disassociating a key from a clojure map

This returns a map without the key-value pairs for the keys mentioned in the function argument. It can be used to remove information from existing map.

(dissoc {:a 1 :b 2} :a) ;; {:b 2}

It can also be used for dissocing multiple keys as:

(dissoc {:a 1 :b 2 :c 3} :a :b) ;; {:c 3}