Recursive Factorial and Fibonacci in Different Languages

gistfile1.scala

def fac(n: Int): BigInt = n match {
  case 0 => 1
  case _ => n * fac(n - 1)
}

def facTail(n: Int, acc: BigInt = 1): BigInt = n match {
  case 0 => acc
  case _ => facTail(n - 1, n * acc)
}


def fib(n: Int): Int = n match {
  case 0 => 0
  case 1 => 1
  case _ => fib(n - 1) + fib(n - 2)
}

def fibTail(n: Int, a: Int = 1, b: Int = 0): Int = n match {
  case 0 => 0
  case 1 => a + b
  case _ => fibTail(n - 1, b, a + b)
}

gistfile2.erl

-module(recursion).
-export([fac/1, fac_tail/1, fib/1, fib_tail/1]).

fac(0) -> 1;
fac(N) when N > 0 -> N * fac(N - 1).

fac_tail(N) -> fac_tail(N, 1).

fac_tail(0, Acc) -> Acc;
fac_tail(N, Acc) when N > 0 -> fac_tail(N - 1, N * Acc).


fib(0) -> 0;
fib(1) -> 1;
fib(N) when N > 1 -> fib(N - 1) + fib(N - 2).

fib_tail(N) -> fib_tail(N, 1, 0).

fib_tail(0, _, _) -> 0;
fib_tail(1, A, B) -> A + B;
fib_tail(N, A, B) when N > 1 -> fib_tail(N - 1, B, A + B).

gistfile3.ex

defmodule Recursion do
  def fac(0) do
    1
  end
  def fac(n) when n > 0 do
    n * fac(n - 1)
  end

  def fac_tail(n) do
    fac_tail(n, 1)
  end

  defp fac_tail(0, acc) do
    acc
  end
  defp fac_tail(n, acc) when n > 0 do
    fac_tail(n - 1, n * acc)
  end

  def fib(0) do
    0
  end
  def fib(1) do
    1
  end
  def fib(n) when n > 1 do
    fib(n - 1) + fib(n - 2)
  end

  def fib_tail(n) do
    fib_tail(n, 1, 0)
  end

  defp fib_tail(0, _, _) do
    0
  end
  defp fib_tail(1, a, b) do
    a + b
  end
  defp fib_tail(n, a, b) when n > 1 do
    fib_tail(n - 1, b, a + b)
  end
end

gistfile4.js

// facs
// 0, 1, 2, 3,  4,   5,   6,    7,     8
// 0, 1, 2, 6, 24, 120, 720, 5040, 40320

function fac(n) {
  if (n === 1) {
    return n;
  }
  return n * fac(n - 1);
}

let facRes = fac(4);

console.log(facRes);

function facTail(n, memo) {
  memo = memo || 1;

  if (n === 1) {
    return memo;
  }
  return facTail(n - 1, n * memo)
}

let facTailRes = facTail(4);

console.log(facTailRes);

// fibs
// 0, 1, 2, 3, 4, 5, 6,  7,  8
// 0, 1, 1, 2, 3, 5, 8, 13, 21

function fib(n) {
  if (n === 0) {
    return 0;
  }
  if (n === 1) {
    return 1;
  }
  return fib(n - 1) + fib(n - 2);
}

let fibRes = fib(8);

console.log(fibRes);

function fibTail(n, a, b) {
  a = a || 0;
  b = b || 1;

  if (n === 0) {
    return 0;
  }
  if (n === 1) {
    return 1;
  }
  if (n === 2) {
    return a + b;
  }
  return fibTail(n - 1, b, a + b);
}

let fibTailRes = fibTail(8);

console.log(fibTailRes);