From: Ross Bamford <rossrt@...>
Date: 2006-11-09T03:19:55+09:00
Subject: Re: Bytecode Compiler (#100)

This quiz has turned out to have some interesting solutions, I'm looking
forward to writing up the summary :) For the record, here's the sample
solution I made when I suggested the quiz to James - it takes a similar
approach to some of the other solutions in letting Ruby's parser do the
heavy lifting. I pulled _why's Sandbox into the mix again to let me keep
dangerously modified core classes on a tight rein.

# --- compiler.rb
require 'sandbox'

class Compiler
  class << self
    def sb
      unless @sb
        @sb = Sandbox.new

        @sb.eval <<-EOC
          class Object
            private
            def ldconsts(o)
              if (o > -32769) && (o < 32768)
                [].push(0x01, *[o].pack('n').unpack('C*'))
              else
                [].push(0x02, *[o].pack('N').unpack('C*'))
              end
            end
          end

          class Fixnum
            def +(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0x0a)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0a)
              end
            end

            def -(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0xa0, 0x0b)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0b)
              end
            end

            def *(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0x0c)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0c)
              end
            end

            def **(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0xa0, 0x0d)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0d)
              end
            end

            def /(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0xa0, 0x0e)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0e)
              end
            end

            def %(o)
              if o.is_a? Array
                o.push(*ldconsts(self)).push(0xa0, 0x0f)
              else
                ldconsts(self).push(*ldconsts(o)).push(0x0f)
              end
            end
          end

          class Array
            def +(o)
              if o.is_a? Array
                o.push(*self).push(0x0a)
              else
                self.push(*ldconsts(o)).push(0x0a)
              end
            end

            def -(o)
              if o.is_a? Array
                o.push(*self).push(0xa0, 0x0b)
              else
                self.push(*ldconsts(o)).push(0x0b)
              end
            end

            def *(o)
              if o.is_a? Array
                o.push(*self).push(0x0c)
              else
                self.push(*ldconsts(o)).push(0x0c)
              end
            end

            def **(o)
              if o.is_a? Array
                o.push(*self).push(0xa0, 0x0d)
              else
                self.push(*ldconsts(o)).push(0x0d)
              end
            end

            def /(o)
              if o.is_a? Array
                o.push(*self).push(0xa0, 0x0e)
              else
                self.push(*ldconsts(o)).push(0x0e)
              end
            end

            def %(o)
              if o.is_a? Array
                o.push(*self).push(0xa0, 0x0f)
              else
                self.push(*ldconsts(o)).push(0x0f)
              end
            end
          end
        EOC
      end

      @sb
    end

    def compile(code)
      [*sb.eval(code)]
    end
  end
end