it would harm performance because it involves parsing all values and
also ways around cases where the title is "function" (lieral text).

> "function() local x=1; return function() x=1-x; return ({'black',
> 'gray'})[x] end end"
> can be way much easier for lua speakers than digging up a bunch of
> documentations to figure out whether it's implemented, or how it can be
> implemented in a language like TeX, or both which is worse.
Really? I have no clue what that function makec clearer than tex. And
one still needs some documentation that explains what it does.

Often there often is a pretty clean way to do it with less code.