Use variants

basic_math_ex2.re

/*
https://www.codewars.com/kata/basic-mathematical-operations

Your task is to create a function that does four basic mathematical operations.

The function should take three arguments - operation(string/char), value1(number), value2(number).
The function should return result of numbers after applying the chosen operation.

basicOp('+', 4, 7)         // Output: 11
basicOp('-', 15, 18)       // Output: -3
basicOp('*', 5, 5)         // Output: 25
basicOp('/', 49, 7)        // Output: 7
*/
type operator = Plus | Minus | Multiply | Divide;

let basicOp3 = (operation, a, b) => {
  switch (operation) {
  | Plus => a + b
  | Minus => a - b
  | Multiply => a * b
  | Divide => a / b
  }
};

Js.log(basicOp3(Plus, 4, 7) == 11);
Js.log(basicOp3(Minus, 15, 18) == -3);
Js.log(basicOp3(Multiply, 5, 5) == 25);
Js.log(basicOp3(Divide, 49, 7) == 7);