[ruby-core:41032] Binding#with

Hi,

I think this toplc might be proving to be too advance for ruby-talk, so I 
would like to ask here among Ruby internals experts.

I originally wrote:

  class Binding
    def with(_hash, &_yield)
      eval("Proc.new{ |#{_hash.keys.join(',')}| binding 
}").call(*_hash.values)
    end
  end

That works for adding locals to binding, but does not allow for calling 
yield. e.g.

  q = 9
  b = binding.with(:a=>1){ |x| x+x }
  b.eval('q')  #=> 9
  b.eval('a')  #=> 1
  b.eval('yield(2)')  #=> Error

So I tried:

  class Binding
    def with(_hash, &_yield)
      code = <<-END
        define_method(:_with) do |#{_hash.keys.join(',')}|
          binding
        end
      END
      (class << self; self; end).class_eval(code)
      b = _with(*_hash.values, &_yield)
      (class << self; self; end).class_eval{ remove_method(:_with) }
      return b
    end
  end

But that looses original closure.

  q = 9
  b = binding.with(:a=>1){ |x| x+x }
  b.eval('q')  #=> Error
  b.eval('a')  #=> 1
  b.eval('yield(2)')  #=> 4

I thought #define_method kept closure?

Is there any way I can keep the closure and get yield to work?

fyi, if wondering why I am doing this, it is b/c ERB takes Binding object. 
I am working on my multi-template system. I want any interface for one 
template engine to be convertible to another's (which I have achieved 
except for this issue).