A replica of Citizen Quartz watch based on Harel's paper introducing statecharts

https://andyjakubowski.github.io/statechart-watch/

by all2 • 10 months ago

146 22 10 months ago

andyjakubowski.github.io

ttd• 10 months ago

If you're fond of state machines as an abstraction for system design, I highly recommend reading the Harel statechart paper. It's well-written and understandable. And, it's truly a useful extension of the type of state machine diagrams software engineers typically produce.

all24• 10 months ago

I discovered the above implementation about the time I finished reading through the paper. I need to go back through and finish taking notes.

I think there might be room to add `any` and `all` guards that take many guards as arguments.

The other thing I've been pondering is the apparent similarity between ASTs and the sort of graph a statechart forms. If we compress state and chart into a single object, now you have states that can have parents and children (the semantics of what is an active state would vary with your node type, IE compound or parallel). Then your edges would the transitions between nodes.

The semantics of the whole thing starts to look vaguely like there's a programming language that could emerge if the intermediate representation is hammered out well enough.

TFortunato• 10 months ago

At Amazon Robotics we built a robot control system that executed state charts (described in an extended version of SCXML) in real-time for managing the core behaviors of the robot.

To help people not have write the charts by hand, we built a DSL (originally in python, then in Kotlin), to author robot behaviors that then compiled down to SCXML. Conditions on guards were written in a tiny expression language we wrote, enabling you to look at various signals from the hardware and software at runtime and make decisions based off them.

The nice part of this setup was that it opened up a path for doing more formal analysis on the behavior. E.g. you could easily find "terminal" states that you could enter but not leave. You can also imagine things like checking things like which states in a parallel or in concurrently running machines, aren't allowed to be active, and verifying there is no path in the state graph that allowed that to occur. There were other nice properties as well, like getting a graphical visualization of your program state "for free"

It was definitely a more constrained model than a "full featured" programming language, but for our use case, controlling machines in a reliable way, it worked out very well!

chermi4• 10 months ago

Is there a modern reference implementation of statecharts? My understanding is that there's tons of offspring and they all kind of disagree. Same with regular FSM at least from limited understanding from this book https://ptolemy.berkeley.edu/books/leeseshia/.

I'm a little worried the author (Lee) may have a particular PoV and perhaps this wasn't the best resource to learn from?

I'm building an automated environmentally monitored +. controlled mushroom fruiting chamber. V1 I got by just with very basic state machines but I'm trying to take it up a notch in sophistication and do it the "right " way.

all24• 10 months ago

There is for JavaScript called XState. I think it is SCXML compliant .You might also take a look at qmuntal/stateless (not SCXML compliant), a golang module. It has rudimentary sub-state functionality.

I'm in the process of writing a golang library, if you're interested in seeing some raw development (IE, I'm in the middle of designing dev UX, and the guts of the lib have yet to be implemented).

You may also consider n8n for your uses. As workflow management goes, it is quite robust.

For embedded work, I honestly don't know. I do know that golang can be transpiled into C (https://tinygo.org/) and tinygo + qmuntal/stateless might work really well for your use-case.

neilv• 10 months ago

It's not available, but I once made a researchy Statechart->Java compiler. For the concurrency, it leaned on Java's green threads.

Since then, I sometimes do manual implementations in code. For example, the Swift code of an iOS app I wrote has an ASCII art diagram of a hierarchical Statechart, for making the UI and NFC event handling solid (despite SwiftUI quirks and inconsistent docs at the time).

RossBencina3• 10 months ago

The ?modern reference specification is UML statecharts. However I'm under the impression that not all features are efficiently implementable. For example Miro Samek's book covers a subset for real-time systems: https://www.state-machine.com/psicc2 I highly recommend that book even if you end up rolling your own implementation.

moolcool• 10 months ago

This is very cool, but why does the battery die so quickly?

jsheard• 10 months ago

Probably to test the "low battery" part of the state machine without having to wait several years.

tentahedronic• 10 months ago

Simply awesome. One thing I would suggest cleaning up is batteryPercentage which shows something ugly like 98.1000000000006 at least for me.

klooney• 10 months ago

Delightful!

RossBencina3• 10 months ago

I always wanted to implement a graphical statechart editor specified in statecharts, or even implemented in executable statecharts.

kloud• 10 months ago

Very cool! I created something similar for Casio F-91W. It also uses XState. The benefit of specifying a machine in XState, is that one can embed Stately editor to visualize the states and their transitions.

https://github.com/dundalek/casio-f91w-fsm

ripe• 10 months ago

Beautiful! I love the clean design of the page, too. I went through a period of obsession with the Harel paper, and your page is a nice summary of some of the key points!

klaff• 10 months ago

Anyone else seeing how fast they can start/stop the stopwatch? I got .08 once but mostly .10-.12.

A replica of Citizen Quartz watch based on Harel's paper introducing statecharts

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