elixir_way.ex

defmodule EmailValidation do
  def validate(email) do
    email_validation_result = {:ok, email}

    check_for_validity(email_validation_result)
    |> check_if_email_taken
  end

  defp check_for_validity({:ok, email}) do
    case check_against_regex(email) do
      :ok -> {:ok, email}
      :error -> {:error, :invalid_address}
    end
  end

  defp check_if_email_taken({:error, reason}), do: {:error, reason}

  defp check_if_email_taken({:ok, email}) do
      query_the_db_blah_blah
  end
end

email_validation.rb

module EmailValidation
  module_function

  def validate(email_string) # joe@harrys.com
    email_validation_structure = ValidationStructure.new(status: :ok, value: email_string)

    step_result = check_for_validity(email_validation_structure)
    check_if_email_already_taken(step_result)
  end

  def check_for_validity(validation_structure)
    return validation_strucutre if validation_strucutre.error?

    if regex_matches_email(validation_strucutre, value)
      validation_structure
    else
      ValidationStructure.new(status: :error, reason: :invalid_email)
    end
  end
  private_module_function :check_for_validity

  def check_if_email_already_taken(validation_structure)
    return validation_strucutre if validation_strucutre.error?

    if email_exists?(validation_structure.value)
      ValidationStructure.new(status: :error, reason: :email_already_taken)
    else
      validation_structure
    end
  end
  private_module_function :check_if_email_already_taken
end

validation_result.rb

# THIS FILE ALREADY EXISTS

class ValidationResult
    def initialize(success: false, error_message: nil, value: value)
        @success = success
        @error_message = error_message
        @value = value
    end

    def success?
        !!success
    end

    def error?
        !success?
    end

    attr_reader :error_message, :value

    private

    attr_reader :success
end