gistfile1.rb

# Befunge-93 interpreter (http://en.wikipedia.org/wiki/Befunge)
class BefungeParser
  attr_accessor :stack, :program, :px, :py, :direction, :debug_mode

  Binary_ops = ['*', '+', '-', '/', '%']

  def initialize(code)
    @stack = []
    @program = []
    @px = 0
    @py = 0
    @direction = :right
    @debug_mode = false

    parse_code(code)
  end

  def parse_code(code)
    code.each_line do |line|
      @program << line.split(//).map do |op|
        #convert ops to Integer if needed
        op = op.to_i if op =~ /\d/
        op
      end
    end
  end

  def run
    string_mode = false

    while get_op && get_op != '@' do
      op = get_op
      
      if debug_mode then
        puts stack.inspect
        puts "#{op} - #{px} - #{py} - #{direction}"
      end

      if string_mode then
        if op == '"' then
          string_mode = false
        else
          @stack << op
        end
      elsif
        #TODO: move this huge block to his own funcion
        case op
        when Integer then @stack << op
        when '#' then move_pointer
        when '"' then string_mode = true
        when ',' then $stdout.putc stack.pop
        when '~' then @stack << $stdin.getc
        when '>' then @direction = :right
        when '<' then @direction = :left
        when 'v' then @direction = :down
        when '^' then @direction = :up
        when '?' then @direction = [:right, :left, :up, :down][rand(4)-1]
        when ':' then @stack << stack.last
        when '!' then @stack << (stack.pop == 0 ? 1 : 0)
        when '$' then @stack.pop
        when 'g' then @stack << program[stack.pop][stack.pop]
        when 'p' then @program[stack.pop][stack.pop] = stack.pop
        when '`' then @stack << (stack.pop < stack.pop) ? 1 : 0
        when '\\' then @stack += [stack.pop, stack.pop]
        when *Binary_ops then @stack << stack.pop.send(op, stack.pop)
        #TODO: dry this up
        when '_'
          val = stack.pop || 0
          @direction = val == 0 ? :right : :left
        when '|'
          val = stack.pop || 0
          @direction = val == 0 ? :down : :up
        end
      end

      move_pointer
    end
  end

  def move_pointer
    case direction
    when :right then @px += 1
    when :left  then @px -= 1
    when :down  then @py += 1
    when :up    then @py -= 1
    end
  end

  def get_op
    program[py][px]
  end
end

code = ARGF.read

parser = BefungeParser.new(code)
parser.run