Brainfuck Interpreter

#!/usr/bin/env ruby

# Brainfuck Interpreter

class Runtime
  
  def initialize(program)
    @data = [0]
    @data_ptr = 0
    @inst_ptr = 0
    @prog = parse(program)

    run
  end

  def expand_array(arr, to_length)
    arr += Array.new(to_length - arr.length, 0) if to_length > arr.length
  end

  def increment_data
    @data[@data_ptr] = (@data[@data_ptr] <= 254) ? @data[@data_ptr] + 1 : 0
  end

  def decrement_data
    @data[@data_ptr] = (@data[@data_ptr] >= 1) ? @data[@data_ptr] - 1 : 255
  end

  def increment_data_ptr
    @data_ptr += 1
    @data = expand_array(@data, @data.length + 1) if @data_ptr >= @data.length - 1
  end

  def decrement_data_ptr
    @data_ptr -= 1
  end

  def output
    print @data[@data_ptr].chr
  end

  def input
    @data[@data_ptr] = STDIN.gets(1).ord
  end

  def loop_open
    @inst_ptr = @prog[@inst_ptr+1..-1].rindex(']') if @data[@data_ptr] == 0
  end

  def loop_close
    @inst_ptr = @prog[1..@inst_ptr].index('[') unless @data[@data_ptr] == 0
  end

  def method_missing(method_symbol)
    case method_symbol.to_s
      when '>' then increment_data_ptr
      when '<' then decrement_data_ptr
      when '+' then increment_data
      when '-' then decrement_data
      when '.' then output
      when ',' then input
      when '[' then loop_open
      when ']' then loop_close
    end 
  end

  def parse(data)
    @prog = data.gsub(/[^><+\-\.,\[\]]/, "").split(//)
  end

  def run
    @inst_ptr = 0
    until @inst_ptr == @prog.length
      self.send(@prog[@inst_ptr])
      @inst_ptr += 1
    end
  end

end

unless ARGV[0].nil?
  if File.exists? ARGV[0]
    interpreter = Runtime.new(File.read(ARGV[0]))
  else
    interpreter = Runtime.new(ARGV[0])
  end
else
  puts "No Brainfuck source file specified, aborting."
end

Your loops are broken, this should be "Hello World!"

>++++++++[<+++++++++>-]<.>>+>+>++>[-]+<[>[->+<<++++>]<<]>.+++++++..+++.>
->+++++++.<+[>[+>]>]<<<+++++++++++++++.>>.+++.------.--------.>>+.>++++.