Find if subarray with given sum exists

subarray_sum.ex

defmodule SubarraySum do
  def run([], val), do: false
  def run([ _ | rest ] = arr, val) do
    run(arr, val, 0) || run(rest, val)
  end

  def run(_, val, val), do: true
  def run([], _val, _res), do: false
  def run(_, val, res) when(val < res), do: false

  def run([ first | rest ], val, res) do
    run(rest, val, first + res)
  end
end

subarray_sum_test.exs

defmodule SubarraySumTest do
  use ExUnit.Case
  test "find if consecutive elements sums to given num" do
    assert SubarraySum.run([1, 3, 4, 5, 2], 12) === true
    assert SubarraySum.run([1, 9, 4, 5, 2], 12) === false
  end
end