Trying ReasonML

euler2.re

/*
Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
*/

let rec evenFibSum = (max_value, prev_num, prev_prev_num, even_sum) => {
  let new_num = prev_num + prev_prev_num;
  if (new_num > max_value) {
    even_sum;
  } else {
    let new_sum = switch new_num {
      | _ when (new_num mod 2 == 0) => even_sum + new_num
      | _ => even_sum
    };
    evenFibSum(max_value, new_num, prev_num, new_sum);
  }
};

Js.log(evenFibSum(4000000, 0, 1, 0));

euler3.re

/*
The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?
*/

let divisible_by = (dividend, divisor) => (dividend mod divisor) == 0;

let rec prime_factors = (n, i, l) => {
  switch i {
    | _ when (n == i) => [n, ...l]
    | _ when (n <= 2) => l
    | _ when divisible_by(n, i) => prime_factors(n / i, 2, [i, ...l]);
    | 2 => prime_factors(n, 3, l);
    | _ => prime_factors(n, i + 2, l);
  };
};

Js.log(prime_factors(87625999, 2, [6857])); /* the proper input number is bigger than an int32 :O */

fibonacci.re

let rec fibonacci = fun(n) => switch n {
  | _ when (n < 2) => 1
  | _ => (fibonacci (n - 1)) + (fibonacci (n - 2))
};

for (x in 1 to 10) {
  Js.log(fibonacci(x));
}

fizzbuzz.re

let fizzbuzz = (n) => switch n {
  | _ when (n mod 15) == 0 => "FizzBuzz"
  | _ when (n mod 3) == 0 => "Fizz"
  | _ when (n mod 5) == 0 => "Buzz"
  | _ => string_of_int(n)
};

for (x in 1 to 20) {
  Js.log(fizzbuzz(x));
}