mango.rb

class Mango

  def initialize(source)
    source.gsub!(/\/[*].*?[*]\//m, ' ') # remove comments
    @toks = source.split(/\s+/)
    @toks = @toks[1..-1] if @toks[0].empty?
    @pc = 0
    @vars = {}
    @vec = []
    @stack = []
    @exit = false
    parse_labels
  end

  def parse_labels
    pos = 0
    while pos < @toks.size
      if /^(\w+):$/ === @toks[pos]
        @vars[$1] = pos
        @toks.slice! pos
      else
        pos += 1
      end
    end
  end

  def run
    while !@exit
      instr = @toks[@pc]
      @pc += 1
      # $stderr.puts "executing `#{instr}'"
      val = case instr
            when /\d+/                    # integer literal
              Integer(instr)
            when /\w+/                    # var, label, or opcode ref
              if self.methods.include? "opc_#{instr}".to_sym
                self.send('opc_' + instr)
              else
                {:sym => instr, :val => @vars[instr]}
              end
            end
      # $stderr.puts " => #{val}"
      @stack.push val unless val.nil?
      # $stderr.puts "stack: #{@stack.reverse.map(&:to_s).join(' ')}"
    end
  end

  def pop(literal=false)
    val = @stack.pop
    if Hash === val
      val = if literal
              val[:sym]
            else
              val[:val]
            end
    end
    # $stderr.print " #{val}"
    val
  end

  def opc_read_num
    Integer($stdin.readline)
  end

  def opc_dup
    val = pop
    # $stderr.print " => #{val}"
    @stack.push val
    val
  end

  def opc_call
    oldpc = @pc
    @pc = pop
    oldpc
  end

  def opc_exit
    @exit = true
    nil
  end

  def opc_add
    pop + pop
  end

  def opc_sub
    - pop + pop
  end

  def opc_mod
    v1 = pop
    v2 = pop
    v2 % v1
  end

  def opc_xor
    pop ^ pop
  end

  def opc_vstore
    val = pop
    loc = pop
    @vec[loc] = val
    nil
  end

  def opc_vload
    @vec[pop]
  end

  def opc_jump
    @pc = pop
    nil
  end

  def opc_store
    name = pop true
    val = pop
    @vars[name] = val
    nil
  end

  def cond_helper
    l_false = pop
    l_true = pop
    cond = yield pop
    @pc = if cond
            l_true
          else
            l_false
          end
    nil
  end

  def opc_ifz
    cond_helper {|c| c == 0}
  end

  def opc_ifg
    cond_helper {|c| c > 0}
  end

  def opc_print_byte
    $stdout.putc pop
    nil
  end

  def opc_print_num
    $stdout.print pop
  end
end


if __FILE__ == $0
  source = File.read(ARGV[0])
  m = Mango.new(source)
  m.run
end