gistfile1.rb

# Ruby assembler DSEL, following tqbf’s unreleased one:
# http://news.ycombinator.com/item?id=378457

$assembly_output = nil

class Program
  def initialize() @contents = [] end
  def add() $assembly_output = self; yield end
  def append(something) @contents.push(something) end
end

class Assembler
  def initialize() 
    @prog = Program.new 
  end

  def instruction(opcode, *args) $assembly_output.append([opcode, args]) end

  def push(arg) instruction("push", arg) end
  def mov(a, b) instruction("mov", a, b) end
  def pop(arg) instruction("pop", arg) end
  def xor(a, b) instruction("xor", a, b) end
  def ret() instruction("ret") end

  def ebx() 'ebx' end
  def eax() 'eax' end
  def method_missing(id, *args) "some label called #{id}" end

  def doit
    @epilog ||= @prog.add {
      push ebx 
      mov ebx, retv
      mov [ebx], eax
      pop ebx
      xor eax, eax
      ret
    }
  end
end

# irb(main):002:0> Assembler.new.doit
# => [["push", ["ebx"]], ["mov", ["ebx", "some label called retv"]], 
# ["mov", [["ebx"], "eax"]], ["pop", ["ebx"]], ["xor", ["eax", "eax"]],
# ["ret", []]]