enum.rb

def enum blk = Proc.new
  m = Module.new
  o = Object.new
  o.instance_eval {
    @enum_idx = -1
    @enum_mod = m
    def method_missing(n, *a)
      n =~ /([A-Z][A-Z_]*)(=)?/
      raise "bad enum name #{n}" unless $1
      if $2
        v = a[0]
      else
        v = @enum_idx + 1
      end
      @enum_idx = v
      @enum_mod.const_set($1, v)
      nil
    end
    instance_exec(self, &blk)
  }
  m
end

E = enum { |e|
  e.FOO
  e.BAR
  e.BAZ = 42
  e.FUGA_QUUX
}

p E::FOO #=> 0
p E::BAR #=> 1
p E::BAZ #=> 42
p E::FUGA_QUUX #=> 43