#---
# Excerpted from "The ThoughtWorks Anthology",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material, 
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/twa for more book information.
#---
# using lists only. Greenspun would love this ;-)


[
  [:item, :secure_air_vent],

  [:item, :acid_bath, 
    [:uses,
        [:acid, 
            [:type, :hcl],
            [:grade, 5]],
        [:electricity, 12]]],
  
  [:item, :camera, 
    [:uses, [:electricity, 1]]],

  [:item, :small_power_plant,
    [:provides, [:electricity, 11]],
    [:depends_on, :secure_air_vent]]]



# interesting note here to rely on tail rather than more nested lists
# eg use [:depends_on, :secure_air_vent, :something_else] rather than
# [:depends_on, [:secure_air_vent, :something_else]]