A very simple toy vm

countdown.asm

push 5
ifeq 4
jump 8
print
push -1
add
jump 2
print

vm.rb

class MochiVM
  def initialize source
    @iptr = 0
    @stack = []
    @program = parse_program(source)
  end

  def parse_program source
    source.lines.to_a.map { |line| line.split(" ") }
  end

  def run
    while @iptr < @program.length
      instr, *values = @program[@iptr]
      send(instr.to_sym, *values)
    end
  end

  def step
    @iptr += 1
  end

  def push num
    @stack.push(num.to_i)
    step
  end

  def pop
    result = @stack.pop
    step
    result
  end

  def add
    @stack.push(@stack.pop + @stack.pop)
    step
  end

  def mult
    @stack.push(@stack.pop * @stack.pop)
    step
  end

  def sub
    top = @stack.pop
    @stack.push(@stack.pop - top)
    step
  end

  def div
    top = @stack.pop
    @stack.push(@stack.pop / top)
    step
  end

  def ifeq address
    if @stack.last != 0
      @iptr = address.to_i - 1
    else
      step
    end
  end

  def jump address
    @iptr = address.to_i - 1
  end

  def print
    puts @stack.last
    step
  end

  def dup
    @stack.push(@stack.last)
    step
  end
end