Make names for unnamed symbol arguments
set_argnames(args, data = args)the unevaluated argument list
the list to be named (args by default)
The elements of an unevaluated list of arguments may or may not
have names as given by user. For example, list.select requires user
to specify the fields to select. These fields are unevaluated arguments,
some of which are symbols and others are calls. For the symbols, it is natural
to make the resulted lists to have the same name for the particular arguments.