# Solved: check if number is prime

Understanding if a number is prime is a fundamental concept in mathematics. Prime numbers have a wide range of applications from cryptography to creating pseudorandom numbers in computer sciences. Today, we’re going to dig into this concept with Haskell, a functional programming language. We’ll begin with the solution, then analyze the code step-by-step. Furthermore, this article includes insights about prime number in different libraries and functions.

Prime numbers are defined as a number that has only two distinct natural number divisors: 1 and itself. The task to check if a number is prime involves determining if the number has any other divisors apart from 1 and itself.

Now, let’s look at the solution in Haskell.

isPrime :: Int -> Bool
isPrime n = null [ x | x <- [2..n - 1], n `mod` x == 0] [/code]

## Understanding the Code

In this code, we have a function called ‘isPrime’, it takes an integer as its argument which returns a boolean value. This function uses the in-built ‘null’ function of Haskell, which checks if the list given to it is empty or not.

The logic of prime number has been implemented in the form of list comprehension. Inside the list comprehension, we are generating a list of numbers from 2 to (n-1) and checking if ‘n’ is divisible by any of these elements.

• [2..n-1] : Generates a list of numbers from 2 to one less than the number.
• n `mod` x : Checks if the number n is divisible by any number in the generated list.

If the number is divisible, then we say that the number is not a prime number, otherwise it is a prime number. The null function checks if the generated list is empty or not. If it is, ‘null’ returns True indicating the number is prime.

## Haskell Libraries and Functions Supporting Prime Checks

Haskell offers a wealth of libraries and functions that can help you in dealing with prime numbers. Some of these include:

• The ‘Numbers’ package provides a range of functions that can sieve prime numbers, generate prime numbers and check primality.
• ‘Math.NumberTheory.Primes’ is another dedicated library for prime number manipulation.
• ‘Arithmoi’ is a Haskell library focused on number theory paradigms. It includes an algorithm for producing prime numbers, factoring compositions and much more.

Although Haskell has in-built library functions, learning and decomposing the logic behind checking prime numbers gives you a stronger foundation of the language and primes you to tackle more advanced problems. This hand-on approach is usually the better one when it comes to understanding the deeper workings of a language like Haskell.

## Further Investigations

Understanding prime number checking forms the basis of many mathematical problems. Besides primality checking, you can also delve into:

• Generating all prime numbers up to a given limit
• Determining the number of prime numbers up to a certain limit (prime counting function)
• Factorizing a number into primes
• All these problems have efficient solutions in Haskell demonstrating the strength and beauty of functional programming in solving mathematical problems.

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