My 'sublist' solution for exercism.io

sublist.exs

defmodule Sublist do

  defp count(l) do
    count(l,0)
  end

  defp count([], size) do
    size
  end

  defp count([_|tail], size) do
    count tail, size+1
  end

  def compare(a,a) do
    :equal
  end


  def compare(a, b) do
    if count(a) > count(b) do
      is_inside(a, b, :superlist)
    else
      is_inside(b, a, :sublist)
    end
  end

  def is_inside(_, [], kind) do
    kind
  end

  def is_inside([], _, _) do
    :unequal
  end

  def is_inside([head_a| tail_a], b, kind) do
    if starts_with([head_a| tail_a], b) do
      kind
    else
      is_inside(tail_a, b, kind)
    end
  end

  def starts_with([], []) do
    true
  end

  def starts_with([], _) do
    false
  end

  def starts_with(_, []) do
   true
  end

  def starts_with([head_a| tail_a], [head_a| tail_b]) do
    starts_with(tail_a, tail_b)
  end

  def starts_with([_head_a| _tail_a], [_head_b| _tail_b]) do
    false
  end

end