[racket] Redex: typesetting variable/label sets

Hi all,

In PL papers, you often see grammars like the following:

  e ::= ... | λx.e | (e e)
  x ∈ Var

In particular, variables are typeset as elements of some set. Often,
there are other sets that might represent labels, locations, tags, and
so on.

I don't see an obvious way to do this kind of typesetting in Redex. My
first thought was to override the typesetting of forms like
`variable-prefix` that I use for variables, but this doesn't work since
I can't change the "::=" in the grammar.

Is my best option to manually build picts for these cases?

Cheers,
Asumu