gistfile1.rb

def coerce_to_array(v)
  if v.IS_A?(Array) # internal test, not #is_a? method call
    v
  elsif v.respond_to?(:to_ary) # replace with to_a for 1.9
    result = v.to_ary
    if result.IS_A?(Array)
      result
    else
      raise TypeError
    end
  else
    [v]
  end
end