elixirで素数の個数判定

PrimeNumCounter.ex

defmodule PrimeNumCounter do
    def count(num) do
        list = [2|makeList(num, [])]
        res = getPrimeList(list, [], trunc(:math.sqrt(num)))
        Enum.count(res)
    end
    def getPrimeList([h|t], result, threshold) do
        if threshold >= h do 
            getPrimeList(sieve(h, t, []), [h|result], threshold)
        else 
            Enum.reverse(result)++[h|t]
        end
    end
    def sieve(num, [h|t], result) do 
        if rem(h, num) != 0 do sieve(num, t, [h|result])
        else sieve(num, t, result)
        end
    end
    def sieve(_, [], result) do Enum.reverse(result)
    end
    def makeList(num, result) do
        if num==2 do result
        else 
        makeList(num-1, [num|result])
        end
    end
end