`valid-transitions` fn? about automat HOT 4 OPEN

Hey @timvisher, just stumbled upon this while looking for a solution myself. I came up with the following:

(defn possible-transitions [compiled-fsm state]
  (let [alphabet (f/alphabet (:fsm (meta compiled-fsm)))]
    (set (filter (fn [t] (a/advance compiled-fsm state t nil)) alphabet))))

This obviously isn't ideal computation-wise but I haven't been able to find the right knobs inside the library to give me the same result. For my use case it's ok.

@ztellman If there's a way to achieve this without brute-force as above an addition to the Readme would be a great :)

from automat.

I just noticed that the above snippet does trigger actions which makes it potentially un-pure making it more or less useless. Anybody came up with a better approach in the meantime that is side-effect free?

from automat.

My new approach looks like this:

(defn dry-run-wrap
  "Wrap `action-fn` so that it only calls `action-fn` if the FSM's state
   does not contain a truthy value under `::dry-run`."
  [action-fn]
  (fn [state input]
    (if (::dry-run state)
      state
      (action-fn state input))))

(defn possible-transitions [compiled-fsm state]
  (let [alphabet (f/alphabet (:fsm (meta compiled-fsm)))
        dry-run  (assoc state ::dry-run true)]
    ;; SIGNAL using [t] here means we assume the FSMs signal function is `first`
    (set (filter (fn [t] (a/advance compiled-fsm dry-run [t] false)) alphabet))))

I'm using dry-run-wrap to wrap action functions so that they are effectively no-ops if the ::dry-run key contains a truthy value.

from automat.

Agree that a way to check what the output states are would be a useful addition to the library, for various introspection abilities and tweaks. (Presumably the viz view function uses some kind of similar hook, but I don't understand the code base well enough to see quite how.)

from automat.