Investigate other nonterminal identification approaches

[noughtmare]

One promising approach is data-reify described in Type Safe Observable Sharing in Haskell. Unfortunately, this isn't straightforward for gigaparsec because our nonterminals might take arguments as input, such as the base of the number parser and the go in the ndots parser. But perhaps it is possible to use a similar approach and get rid of the unsafe ... ::= labels.

Or perhaps there are other approaches that do work for our use case.