Gemfile

source "https://rubygems.org"

gem 'oga'

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    ansi (1.5.0)
    ast (2.3.0)
    oga (2.8)
      ast
      ruby-ll (~> 2.1)
    ruby-ll (2.1.2)
      ansi
      ast

PLATFORMS
  ruby

DEPENDENCIES
  oga

BUNDLED WITH
   1.13.6

willem_detector.rb

require 'open-uri'
require 'oga'

(1970..1990).each do |year|
  body = URI("http://www.meertens.knaw.nl/nvb/topnamen/land/Nederland/#{year}").open.read
  doc = Oga.parse_html(body)
  doc.css('#topnamen-jongens tr').each do |row|
    next unless row.text.include?('Willem')
    puts "##{row.css('td')[0].text} in #{year}"
  end
end