gistfile1.rb

# A very simple Brainfuck interpreter
class BFParser
  attr_accessor :memory, :loop_out, :loop_in, :code_size, :code

  def initialize(code, stack_size = 10000)
    @memory = [0] * stack_size
    @code = code.split(//)
    @code_size = code.length
  
    @loop_in = []
    @loop_out = []
  end

  def run
    parse_loops(code)
    cp = -1 #code pointer
    mp = 0  #memory pointer

    while cp < code_size do
      cp += 1

      case code[cp]
        when '>' then mp += 1
        when '<' then mp -= 1
        when '+' then memory[mp] += 1
        when '-' then memory[mp] -= 1
        when '.' then $stdout.putc memory[mp]
        when ',' then memory[mp] = $stdin.getc
        when '[' then cp = loop_out[cp] if memory[mp] <= 0
        when ']' then cp = loop_in[cp] - 1
      end
    end
  end

  # Simply pre parse the loops in the code
  # loop
  def parse_loops(code)
    tmp = []

    code.each_with_index do |op, n|
      if op == '['
        tmp << n
      elsif op == ']'
        loop_in[n] = tmp.pop
        loop_out[loop_in[n]] = n
      end
    end
  end
end

#code = ARGF.read

#hello world
code = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."

parser = BFParser.new(code)
parser.run