define.rb

class Var
  attr_reader :meta, :namespace, :name

  def self.intern(namespace, name, init = nil)
    @@vars ||= {}
    @@vars[name] = begin
                     v = Var.new(nil, namespace, name)
                     v.set(init) if init
                     v
                   end
  end

  def self.lookup(name)
    @@vars[name]
  end

  def initialize(meta, namesapce, name)
    @meta ||= {}
    @namespace = namespace
    @name = name
  end

  def dynamic?
    @meta[:dynamic]
  end

  def set_dynamic
    @meta[:dynamic] = true
  end

  # TODO: add watchers and validation
  def set(value)
    if dynamic? or @value.nil?
      @value = value
    else
      raise "Can't set a Var once it's been set"
    end
  end

  def get
    @value
  end
end

def define(definition)
  name = definition.keys.first
  init = definition.values.first
  Var.intern(self.class.to_s.to_sym, name, init)
  define_singleton_method name do
    v = Var.lookup(name)
    p v
    v.get
  end

  define_singleton_method :"#{name}=" do |value|
    Var.lookup(name).set(value)
  end
end

define x: 1
p x
x = 4
p x