by @yokolet

Level: easy

Function with let and Destructuring

In Clojure, assignements are done with bindings. Even when you’re within a function definition, assignments are done by bindings. We want variables to be available only within that function. Otherwise, the code may be buggy because other functions may be affected by value changes.

Clojure programmers use let binding for local variables that work only within the functions.

Here’s a simple example. We could write the code below without using the let binding. However, using let makes the last form simpler.

user=> (question "Mary" "John")
"Hey Mary, are Mary's and John's the same?"


We can even bind a function as a value. This helps us avoid repetition or perform pre-processing.

user=> (question "Mary" "John")
"Hey Mary, are Mary's and John's the same?"


Let’s look at one more example. This example tests if the three numbers given will create a right triangle. When a (adjacent), b (opposite), and c (hypotenuse) are given, the function tests a * a + b * b = c * c . The function assumes three values will be given as a vector, [a b c].

user=> (right-triangle? [1 2 3])
false
user=> (right-triangle? [3 4 5])
true
user=> (right-triangle? [5 6 7])
false


The right-triangle? function above uses the nth function to get the adjacent, opposite and hypotenuse values. The nth function works, but Clojure has a smart way of assigning values. It is destructuring. The function right-triangle2? below uses destructuring in function arguments. Without any additional functions or preprocessing, we can assign three values at the same time.

user=> (right-triangle2? [1 2 3])
false
user=> (right-triangle2? [3 4 5])
true
user=> (right-triangle2? [5 6 7])
false

user=> ; we can do above three in a single line using map function
user=> (map right-triangle2? [[1 2 3] [3 4 5] [5 6 7]])
(false true false)

References