class Opal::Nodes::SuperNode

def formal_block_parameter
  case containing_def_scope
    when Opal::Nodes::IterNode
      containing_def_scope.extract_block_arg
    when Opal::Nodes::DefNode
      containing_def_scope.block_arg
    else
      raise "Don't know what to do with scope #{containing_def_scope}"
  end
end