I would argue that Tcl is almost "bicameral" in the OP's sense. The application of the "dodekalogue" rules - https://wiki.tcl-lang.org/page/Dodekalogue - largely corresponds to the "Reader". It goes further in that it also specifies substitution and evaluation rules, but it is similar in that it only applies a few basic structural rules, and knows nothing about the specifics of individual commands.

Tcl's equivalent of the "Parser" is built-in to each command, which decides whether to interpret its arguments as data, code, option flags, etc..

I suspect this division of responsibilities is very helpful for metaprogramming techniques.