Question

Implement a function in OCaml that takes a number as an input and checks whether it is a prime number. The result should be a Boolean value.

Answer 1

Hello,

Before giving answer to the question first check what is prime number?

Ans : Prime number is a number which is divisible by 1 or itself.

Ex; 2,3,5,7

Code:

let prime : int -> bool
= fun number ->
  match number with
     0 -> false
   | 1 -> false
   | _ -> let a = (number - 1) in
            let rec checkZero a number =
              match a with
                 1 -> true
               | _ -> match number mod a with
                         0 -> false
                       | _ -> checkZero (a - 1) number
              in
              checkZero a number
;;

Code Explanation:

Step 1: First check if a number is 0 or 1 return false. because they are not a prime number.
Step 2: We need to divide an input number, say 17 from values 2 to 17 and check the remainder. If remainder is 0 number is not prime. No number is divisible by more than half of itself.
Test Result: 

Please let me know if you have any questions in comments section.

Thanks.

# let prime: int -> bool # = fun number -> # match number with # 0 -> false 1-> false >let a = (number - 1) in let rec checkZero a number = match a with 1 -> true .->match number mod a with 0 -> false -> checkZero (a - 1) number in checkZero a number # ;; val prime int -> bool = <fun> # prime 5;; : bool = true # prime 6;; : bool = false