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# Creating our own map in Clojure on the nail π©βπ­π¨βπ­

## Prologue π§

In many programming languages, map is the name of a higher-order function that applies a given function to each element of a functor, a list, returning a list of results in the same order. It is often called apply-to-all when considered in functional form.

The concept of a map is not limited to lists: it works for sequential containers, tree-like containers, or even abstract containers such as futures and promises.

let's assume we have an array with 5 values

``````(def values [22 33 11 23 15])
``````

## The native map π΄

This way we will apply the native form to iterate the values

``````(map println values)
;this will print each value
``````

## Our own map π

``````(defn my-map
[function sequence]
(let [firsElement (first sequence)]
(if firsElement
(do
(function firsElement)
(my-map function (rest sequence))))))
``````

Now we can use our map to iterate or pass any function to do something, let's implements an example, calculate the square of each element π€

``````(defn my-map
[function sequence]
(let [firsElement (first sequence)]
(if firsElement
(do
(function firsElement)
(my-map function (rest sequence))))))

(defn square [value] (* value value))

(println (my-map square value))
``````

But if we have thousand of elements this possible throw a stackoverflow exception because normal recursion is a call stack, and a stack can be fully populated π

## The ninja way (who prevents stackoverflow exception)π±βπ€

### Tail Recursion

In clojure the `recur` is a way to transform a recursion into a otimized loop, for this purpose is the best way

``````(defn my-map
[function sequence]
(let [firsElement (first sequence)]
(if firsElement
(do
(function firsElement)
(recur function (rest sequence))))))

(defn square [value] (* value value))

(println (my-map square value))
``````

Just for today, feel free to comment, I'm still learning and I usually share whenever I can, because I'm adept at learning public π€