exercism/elixir/isogram/lib/isogram.ex

defmodule Isogram do
  @doc """
  Determines if a word or sentence is an isogram
  """
  @isogram ~r/(\w).*\1/i

  @spec isogram?(String.t()) :: boolean
  def isogram?(sentence), do: !Regex.match?(@isogram, String.downcase(sentence))
end