2fi4-collection-functions.md

Collection Functions

#clojure #language #programming #functions

The main function of Collection Abstraction is into, that catch elements from one collection (second) and add to another one (first):

(map identity {:sunlight-reaction "Glitter!"})
; => ([:sunlight-reaction "Glitter!"])

(into {} (map identity {:sunlight-reaction "Glitter!"}))
; => {:sunlight-reaction "Glitter!"}

Conj

It does the same as into but with scalar. It is common two functions do the same in Clojure, however one with scalar and another one with collections.

(conj [0] 1)
; => [0 1]

Apply

Explode the elements of a sequence and apply the function on it

(apply max[0 1 2])
; => 2

Partial

Return a new function with part of it filled with values

(def add 10 (partial +10))
(add10 3)
; => 13

(defn my-partial
	[partialized-fn & args]
	(fn [& more-args]
	  (apply partialized-fn (into args more-args))))

(def add20 (my-partial + 20))
(add20 3)
; => 23

The example above, the value of add20 is the anonymous function returned by my-partial.

Complement

;; Define a predicate function that checks if a number is even
(defn even? [n]
  (zero? (mod n 2)))

;; Use complement to create a predicate that checks if a number is not even (i.e., odd)
(def odd? (complement even?))

;; Test the complement function
; =>(println (even? 4))  ;; Output: true
; =>(println (odd? 4))   ;; Output: false
; =>(println (even? 5))  ;; Output: false
; =>(println (odd? 5))   ;; Output: true

References

• Higginbotham, 2015, p88-93