Using the mops Timer Tool library

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Every timer carries an action (a function) which cannot be persisted, so a setup is necessary.

@luc-blaeser came up with a neat way to do this using a transient let:

import { setTimer } = "mo:base/Timer"

actor {
  func computeExpiry() : Nat = 42;

  func action() : async () {
    // do whatever
    /*timerId :=*/ ignore setTimer<system>(#seconds (computeExpiry()), action);
  };
  // on top-level
  transient var timerId = setTimer<system>(#seconds (computeExpiry()), func() : async () { await action() });
};

transient bindings always get reinitialised when the actor is upgraded, so there is a guarantee that action will trigger sometime.

Hope this helps. (Edited the example, but I keep running into the circularity problem, and it is too late here. Will fix it tomorrow.)

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