Problems from scala course to elixir

balance.ex

defmodule Balance do
  def balance str  do
    balance(str, 0)
  end
  defp balance str, parenthesis_count do
    if String.length(str) == 0 do
      parenthesis_count == 0
    else if parenthesis_count < 0 do
      false
    else
      {head, tail} = String.next_codepoint(str)
      parenthesis_count_acc = parenthesis_count
      cond do
        head == "(" ->
          parenthesis_count_acc = parenthesis_count_acc + 1
        head == ")" ->
          parenthesis_count_acc = parenthesis_count_acc - 1
        true ->
      end
      balance(tail, parenthesis_count_acc)
    end
    end
  end
end

balance_suite_test.exs

defmodule BalanceSuiteTest do
  use ExUnit.Case
  import Balance

  test 'balance: "(if (zero? x) max (/ 1 x))" is balanced' do
    assert balance("(if (zero? x) max (/ 1 x))")
  end

  test 'balance: "I told him ..." is balanced' do
    assert balance("I told him ...")
  end

  test 'balance: ":-)" is unbalanced' do
    assert !balance(":-)")
  end

  test 'balance: counting is not enough' do
    assert !balance("())(")
  end
end

count_change.ex

defmodule CountChange do

  def count_change money, change_list do
    cond do
      money == 0 ->
        1
      money < 0 ->
        0
      length(change_list) == 0 ->
        0
      true -> # else
        [head|tail] = change_list
        count_change(money - head, change_list) +
          count_change(money, tail)
    end
  end
end

count_change_test.exs

defmodule CountChangeTest do
  use ExUnit.Case
  import CountChange

  test 'countChange: example given in instructions' do
    assert count_change(4, [1,2]) == 3
  end

  test 'countChange: sorted CHF' do
    assert count_change(300, [5,10,20,50,100,200,500]) === 1022
  end

  test 'countChange: no pennies' do
    assert count_change(301, [5,10,20,50,100,200,500] ) === 0
  end

  test('countChange: unsorted CHF') do
    assert count_change(300, [500,5,50,100,20,200,10]) === 1022
  end

end

pascal.ex

defmodule Pascal do

  def pascal column, row do
    if column == 0 || row == column do
      1
    else
      pascal(column, row - 1) + pascal( column - 1, row - 1 )
    end
  end

end

pascal_suite_test.exs

defmodule PascalSuiteTest do
  use ExUnit.Case
  import Pascal

  test 'pascal: col=0, row=2' do
    assert pascal(0,2) == 1
  end

  test 'pascal: col=1, row=2' do
    assert pascal(1,2) == 2
  end

  test 'pascal: col=1, row=3' do
    assert pascal(1,3) == 3
  end
end