arduino_program_interpreter.rb

class ArduinoInterpreter
  def initialize(setup_block, tick_block)
    @setup_block, @tick_block = setup_block, tick_block
  end
  
  def serial_begin
    puts "Initialising serial port..."
  end
  
  def serial_write(data)
    puts data
  end 
end

class ArduinoProgram
  def setup(&setup_block)
    puts "Saving setup block..."
    @setup_block = setup_block
  end
  
  def tick(&tick_block)
    puts "Saving tick block..."
    @tick_block = tick_block
  end
  
  def run
    # @setup_block and @tick_block are ArduinoProgram vars passed into #setup and #tick
    ArduinoInterpreter.new(@setup_block, @tick_block).instance_eval do
      # instance_exec(&@ivar to find in an ArduinoInterpreter)
      instance_exec(&@setup_block)

      # This actually fails... @setup_block is found in the ArduinoInterpreter, but
      # the value of `self` reverts to the ArduinoProgram, so the block can't find the
      # method #serial_begin
      #
      # @setup_block.call

      loop do
        instance_exec(&@tick_block)
        sleep 1
      end            
    end
  end
end

def arduino_program(&block)
  program = ArduinoProgram.new
  program.instance_eval(&block)
  program
end

tick_tock = arduino_program do
  setup do
    serial_begin
  end
  
  tick do
    serial_write "tock"
  end
end

tick_tock.run

this_works_but_you_can_vandalise_it.rb

class ArduinoProgram
  def setup(&setup_block)
    puts "Saving setup block..."
    @setup_block = setup_block
  end
  
  def tick(&tick_block)
    puts "Saving tick block..."
    @tick_block = tick_block
  end
  
  def run
    @setup_block.call
    loop do
      @tick_block.call
      sleep 1
    end      
  end
  
  private
  
  def serial_begin
    puts "Initialising serial port..."
  end
  
  def serial_write(data)
    puts data
  end
end

def arduino_program(&block)
  ArduinoProgram.new.tap do |program|
    program.instance_eval(&block)    
  end
end

tick_tock = arduino_program do
  setup do
    serial_begin
    # Let's vandalise the application by calling a program DSL
    # method instead of an interpreter method...
    run
  end
  
  tick do
    serial_write "tock"
  end
end

tick_tock.run

why_doesnt_this_work.rb

class ArduinoInterpreter
  def serial_begin
    puts "Initialising serial port..."
  end
  
  def serial_write(data)
    puts data
  end 
end

class ArduinoProgram
  def setup(&setup_block)
    puts "Saving setup block..."
    @setup_block = setup_block
  end
  
  def tick(&tick_block)
    puts "Saving tick block..."
    @tick_block = tick_block
  end
  
  def run
    setup_block, tick_block = @setup_block, @tick_block
    
    interpreter = ArduinoInterpreter.new
    interpreter.instance_eval do
      setup_block.call
      loop do
        tick_block.call
        sleep 1
      end            
    end
  end
end

def arduino_program(&block)
  ArduinoProgram.new.tap do |program|
    program.instance_eval(&block)    
  end
end

tick_tock = arduino_program do
  setup do
    serial_begin
  end
  
  tick do
    serial_write "tock"
  end
end

tick_tock.run