Logic and constraints

Setup

Connect this notebook to a running iex --sname al -S mix session first — see the intro for connection steps.

AL.Branch.head()

Run a method backwards

run do
  factorial(n, 120)
end

Propagate constraints about and between objects

run do
  defclass :rectangle, super: :value, ivars: [:width, :height, :perimeter] do
    defmethod(:init, [self, args, new]) do
      slot_get(args, :width, w)
      slot_get(args, :height, h)
      slot_get(args, :perimeter, p)
      eq(p, 2 * w + 2 * h)
      unify(new, %{class: :rectangle, width: w, height: h, perimeter: p})
    end

    defmethod(:get_slot, [self, k, v]) do
      vm_map_get(self, k, v)
    end

    defmethod(:area, [self, result]) do
      get_slot(self, :width, w)
      get_slot(self, :height, h)
      vm_is(result, w * h)
    end
  end

  new(:rectangle, %{width: w, height: 3, perimeter: 16}, r)
  area(r, a)
end

Infer an object's identity from its class and a slot

An open receiver turns the last two calls below into a search, not a lookup.

run do
  defclass :vehicle, super: :object do
  end

  defclass :car, super: :vehicle do
  end

  defclass :bicycle, super: :vehicle do
  end

  defclass :fire_hydrant, super: :object do
  end

  set_slots(:car, %{color: :red})
  set_slots(:bicycle, %{color: :blue})
  set_slots(:fire_hydrant, %{color: :red})

  new(:car, my_car)
  new(:bicycle, my_bike)
  new(:fire_hydrant, hydrant)

  class(x, :vehicle)
  get_slot(x, :color, :red)
end

dif and all_dif

in_domain and label