Guard clauses vs If

guard_if.exs

defmodule GuardIf do
  def if_double(0), do: [0]
  def if_double(n) do
    if rem(n, 2) == 0 do
      if_double(n - 1) ++ [n]
    else
      if_double(n - 1)
    end
  end
  
  def guard_double(0), do: [0]
  def guard_double(n) when rem(n, 2) == 0 do
    guard_double(n - 1) ++ [n]
  end
  def guard_double(n) do
    guard_double(n - 1)
  end
end

GuardIf.if_double(20)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

GuardIf.guard_double(20)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]