semantic operation in simpleparse?

[Fortepianissimo]

A while ago I decided to use simpleparse to write a parser for a kind
of formula representation that I created. This representation is
typed, so there're invalid parses to reject based on sematnics ground
(type mismatch, etc.) I checked simpleparse documentation, and the
only thing which seems to be close is this CallTag thing, but it
doesn't seem to be able to block a parse.

I'd appreciate if someone can show me some example code doing this -
just a skeleton of things. Thank you!