Improvement

[tehrun]

Firstly, I'd like to thank you for the amazing tutorial.

For the partial occurrence, I'd format both value and head to downcase and then return head inside the list to keep the original value:

  def partial_occurrence([], _value), do: []
  def partial_occurrence([head | tail], value) do
    if String.contains?(format_string(head), format_string(value)) do
      [head | partial_occurrence(tail, value)]
    else
      partial_occurrence(tail, value)
    end
  end

  defp format_string(value) do
    value
    |> String.downcase()
  end