require 'ripper'
class Array
  def prepend(x)
    [x] + self
  end
end

def libs(code)
  Ripper.lex(code).
    map {|pos, event, value| [event, value] }.
    select {|event, value| event == :on_const or event == :on_op && value == '::' }.
    map {|event, value| value }.
    prepend(nil).
    each_cons(2).inject([]) {|memo, (before, e)| before == '::' || e == '::' ?  memo : memo << e }
end

code = <<EOF
Nokogiri::HTML('<b>hello Twitter</b>')
p Time.now
EOF

p libs code
#=> ["Nokogiri", "Time"]