def set_block_argument_names
      @block_argument_names = if has_block? && element[2].is_a?(Sexp) # HACK: for lambdas
                                element[2].drop(1).map { |argument| argument }
                              end || []
    end
def set_block_argument_names
      @block_argument_names = if has_block? && element[2].is_a?(Sexp) # HACK: for lambdas
                                element[2].drop(1).map { |argument| argument }
                              end || []
    end
TODO: write specs for lambdas and procs