Is there a standard Backus-Naur form for checking that lists contain consistent token types?

Question

I'm using PLY to parse DNET files. Part of the grammar suggested by the DNET specification is (in my words):

<value>  -> NUMBER | STRING | ID
<values> -> <value> | <values> COMMA <value>
<list>   -> LPAREN <values> RPAREN | LPAREN RPAREN

This works fine if I don't care about mixing token types within a list. However, if I want to be sure that the parser only produces valid lists, it would be great if I could guarantee consistent token types within the list.

My intuition was to define a list production for each valid union of token types, and then use that list production where needed. For example, if I wanted to guarantee I have a list of STRING tokens:

<strings>     -> STRING | <strings> COMMA STRING
<string_list> -> LPAREN <strings> RPAREN | LPAREN RPAREN

But this means I would have to define a bajillion different list productions. Is there a smarter way to do this at the parser level, or should I save this sort of validation to be executed on the AST that I build?