def on_send(node)
      _target, _method, _args = node.children

      if _method == :!
        case @truth.fetch(_target, process(_target))
        when :true
          :false
        when :false
          :true
        else
          nil
        end
      else
        nil
      end
    end
def on_send(node)
      _target, _method, _args = node.children

      if _method == :!
        case @truth.fetch(_target, process(_target))
        when :true
          :false
        when :false
          :true
        else
          nil
        end
      else
        nil
      end
    end
Handles the `!` statement.


 node - the node to evaluate.

 Returns the inverse of the child expression.