Problem 31 - Sieve of Eratosthenes

isPrime : Int -> Bool
isPrime n =
    if n < 2 then
        False
    else
        eratos (abs n) (List.range 2 (n // 2))


eratos : Int -> List Int -> Bool
eratos n cs =
    case cs of
        [] ->
            True

        x :: xs ->
            if n % x == 0 then
                False
            else
                eratos n (List.filter (\y -> (y % x) /= 0) xs)

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