How to model queries in F-Model

[vabatta]

Hi,

I've been going through the docs and I'm struggling to understand how would I model a query which represents a user action. (ref: https://fraktalio.com/fmodel/docs/application/architecture)

Imagine I have a registration form with multiple steps, and at each step I want to validate the form for a meaningful feedback to the user in case of conflicts or errors.
Modelled in a CQRS ES system, my application would expose a port validateUserEmail which does not produce any event (as no state would be changed) and would return a value representing the validation of such email.

As I can understand through the docs, F-Model provides a decider (command, state) -> events but in such a case it would rather be something like (query, state) -> yes | no.