General Problem Solver ver.01 『実践Common Lisp』より

gps.rb

class Operator < Struct.new(:action, :preconds, :addlist, :dellist)
  def appropriate? goal
    self.addlist.include? goal
  end

  def to_s
    self.action.to_s.gsub('_', ' ')
  end
end

class GPS
  attr_accessor :state

  def initialize state, ops
    @state = state
    @ops   = ops
  end

  def solve? goals
    puts "===> [Start] "
    results = goals.all? { |goal| archive? goal }
    puts "<=== [End]"
    return results
  end

  def match_operators goal
    @ops.select { |op| op.appropriate? goal }
  end

  def archive? goal
    apply_result = match_operators(goal).any? { |op| apply! op }
    @state.include?(goal) || !!(apply_result)
  end

  def apply! op
    if op.preconds.all? {|precond| archive? precond}
      puts "Do: #{op}"
      @state = op.dellist.to_a + @state
      @state = op.addlist.to_a + @state
      true
    end
    false
  end
end

testdata = [Operator.new(:drive_son_to_school,
                         [:son_at_home, :car_works],
                         [:son_at_school],
                         [:son_at_home]),
            Operator.new(:shop_installs_battery,
                         [:car_needs_battery, :shop_knows_problem, :shop_has_money],
                         [:car_works]),
            Operator.new(:tell_shop_problem,
                         [:in_communication_with_shop],
                         [:shop_knows_problem]),
            Operator.new(:telephone_shop,
                         [:know_phone_number],
                         [:in_communication_with_shop]),
            Operator.new(:look_up_number,
                         [:have_phone_book],
                         [:know_phone_number]),
            Operator.new(:give_shop_money,
                         [:have_money],
                         [:shop_has_money],
                         [:have_money])]

gps2 = GPS.new([:son_at_home, :car_needs_battery, :have_money, :have_phone_book],
               testdata)
p gps2.solve? [:son_at_school]

result.txt

===> [Start] 
Do: look up number
Do: telephone shop
Do: tell shop problem
Do: give shop money
Do: shop installs battery
Do: drive son to school
<=== [End]
true