```ruby
# Copyright (C) 2016 Colin Fulton
# All rights reserved.
#
# This software may be modified and distributed under the
# terms of the three-clause BSD license. See LICENSE.txt
# (located in root directory of this project) for details.

module Lextacular
  class GroupNode
    def initialize *children
      @children = children
    end

    def to_s
      @children.map(&:to_s).join
    end

    def size
      @children.map(&:size).inject(&:+) || 0
    end
  end
end
```

Add block argument to GroupNode.new
user
```ruby
# Copyright (C) 2016 Colin Fulton
# All rights reserved.
#
# This software may be modified and distributed under the
# terms of the three-clause BSD license. See LICENSE.txt
# (located in root directory of this project) for details.

module Lextacular
  class GroupNode
    def initialize *children, &block
      @children = children
      instance_eval &block if block_given?
    end

    def to_s
      @children.map(&:to_s).join
    end

    def size
      @children.map(&:size).inject(&:+) || 0
    end
  end
end
```
assistant