Now, I don't know how old this pattern is, or whether it was already commonplace 15 years ago. I was introduced to these ideas first through Redux, then learned Elm, the found SAM.
SAM fixes three approximations that we have been using in Software Engineering for Decades:
- actions can manipulate application state
- assignments are equivalent to mutation
- there is no need to define precisely what is a programming step (for instance when you write a = b + c, is that a step or is it 3 steps: read b,c, compute b+c, mutate the value of a)
To a certain degree, Redux and Elm are trying to address these three approximations as well, but they do it from a FP point of view, not from a TLA+ point of view.
Their definition of action aligns with the one of event and their approach to mutation is immutability. The main difference between SAM and Redux/Elm is the way side-effects are treated. SAM embraces side-effects (in particular asynch calls) while Redux/Elm don't know how to deal with them. Redux for instance breaks its principle #1 (single state tree) by introducing Sagas.
SAM is a factoring of your code that fits in one line of code: V = State(Model.present(Action(event))).then(nextAction)
No need for a nebula of libraries or inventing a whole new language.