_fields.html.haml

- fields_for @user do |f|
  
  .email
    %label{:for => "email"} email
    = f.text_field :email
    = f.error_message_on :email
  
  .password
    %label{:for => "password"} password
    = f.password_field :password
    = f.error_message_on :password
  
  .password_confirmation
    %label{:for => "password_confirmation"} confirm password
    = f.password_field :password_confirmation
    = f.error_message_on :password_confirmation

  .gender
    %label{:for => "gender"} gender
    = f.select :gender, select_opts(:gender)
    = f.error_message_on :gender

  .year
    %label{:for => "year"} year of birth
    = f.select :year, select_opts(:year_of_birth)
    = f.error_message_on :year

users_helper.rb

module UsersHelper
  def select_opts(sym)
    case sym
    when :gender then gender
    when :year_of_birth then year_of_birth
    else nil
    end
  end
  
  private
  def gender
    [nil, "f", "m"]
  end
  
  def year_of_birth
    this_year = Time.now.strftime("%Y").to_i
    [nil] + ((this_year-100)..this_year).to_a.reverse
  end
end