#---
# 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 hashes to encode most data but not going all the way



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]