Immutable collections

As we have discussed, immutable data structures cannot be changed. So when you run a function over a collection a copy of that collection is returned. Lets see this by running some code in the REPL.

Note Define a data structure called numbers using a vector. Then write a function that uses the map and inc function to increment all the numbers in a vector.

Then check the current value of the numbers data structure by evaluating its name.

;; define the data structure 
(defn numbers [1 2 3 4 5])

;; increment the numbers
(map inc numbers)

;; see the current value of numbers
numbers

Note Use the conj function to first add the number 5 to the numbers vector from the previous exercise and check the value of numbers. Then add the number 6 to the numbers vector and check the value of numbers.

Finally, use the conj function to add both 5 and 6 to the numbers vector and check the value of numbers

(def numbers [1 2 3 4])

;; add 5 to the numbers vector
(conj numbers 5)

;; check the value of numbers
numbers
;; => [1 2 3 4]

;; add 6 to the numbers vector
(conj numbers 6)

;; check the value of numbers
numbers
;; => [1 2 3 4]

;; add 5 and 6 to the numbers vector
(conj numbers 5 6)

;; Alternatively, you can use the threading macro to chain two conj function calls
(-> numbers
    (conj 5)
    (conj 6))

;; check the value of numbers
numbers
;; => [1 2 3 4]

So even though we have applied several functions on the numbers data structure it still has the same value.