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Managing State with Signals
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Re: Managing State with Signals
#22It's interesting how every build system, frontend framework, programming language implements its own promise pipeline/delayed execution/observables/event propagation. But the implementations are rarely extracted out for general purpose usage and rarely have a rich API. I've been thinking a lot about a general purpose "epoll" which be registered on objects that change. I want to be able to register a reaction to a seq…
> [constraints] the implementations are rarely extracted out for general purpose usage and rarely have a rich API.
Yes.
One of the goals for Objective-S [1] was that it should be possible to build constraints using the mechanisms of the language (so not hardcoded into the language), but then have them work as if they were built into the language.
Part of that was defining how they should look, roughly, and figuring out the architectural structure. I did this in Constraints as Polymorphic Connects [2].
For syntax, I use the symbol |= for a one-way dataflow constraint and =|= for a two-way dataflow constraint. This combines the := that we use for assignment and the | we use for dataflow. Also relates the whole thing to the idea of a "permanent assignment", which I think was introduced in CPL. The structure is simple and general: you need stores that can notify when they are changed, and a copy-element that then copies the data over. At least for one-level constraint. If you want to have multiple levels, you can
I was very surprised and happy when I discovered that I had actually figured this out, sort of by accident, when I did Storage Combinators [3]. There is a generic store that does the notifications, which you can compose with any other store. The notifications get sent to a "copier" stream which then copies the changed element. Very easy. And general, as it works for any store.
For example, I have been using this to sync up UI with internal state, or two filesystem directories. And when I added a store for SFTP support, syncing to SFTP worked out-of-the-box without any additional work. ("Dropbox in a line of code" is a slogan a colleague came up with, and it's pretty close though of course not 100%)
[1] http://objective.st (Site currently being revamped)
[2] https://dl.acm.org/doi/10.1145/2889443.2889456?cid=813164912... / http://www.hpi.uni-potsdam.de/hirschfeld/publications/media/...
[3] https://dl.acm.org/doi/10.1145/3359591.3359729 / https://www.hpi.uni-potsdam.de/hirschfeld/publications/media...
Re: Managing State with Signals
#23Earlier quoted context omitted.
"It's interesting how every build system, frontend framework, programming language implements its own promise pipeline/delayed execution/observables/event propagation." This rings so true to me. I've recently realized how every single non trivial part of my app is in fact a workflow problem : it could be ideally written as a pipe of asynchronous steps, glued together. It's true both for the frontend part and the back…
Thanks for this thoughtful and insightful comment. Many problems can be workflow problems, sometimes even pulling in a rule engine, or require a job queue to do things that can fail. Then you have software such as https://temporal.io/ which is really powerful for resilient workflows. Imagine coordinating the user with a workflow with asynchronous data collection steps. Imagine programming "reaction to user behaviour…
Thanks for the compliment. Since you seem to like it, i’ll emphasis a little as to how i came to realize that :
It’s very common that workflows are suited for data manipulation: write the data to disk, when it’s complete send it to the network, then once it’s completed, etc. I/O are known to be asynchronous, so we’re already equiped for that.
What i noticed is that the screen of your app is also a source of asynchrony, and as such, everytime we interact with it (animations, transitions, waiting for user interactions), we’re actually dealing with problems of exactly the same nature.
Re: Managing State with Signals
#24Earlier quoted context omitted.
Thanks for this thoughtful and insightful comment. Many problems can be workflow problems, sometimes even pulling in a rule engine, or require a job queue to do things that can fail. Then you have software such as https://temporal.io/ which is really powerful for resilient workflows. Imagine coordinating the user with a workflow with asynchronous data collection steps. Imagine programming "reaction to user behaviour…
This workflow engine of yours seems to expect a very predictable and linear sequence of actions. What happens if the user clicks "log out" after user.tutorial(); It's basically making an already easy case easier.
Real workflow engines (the ones you find in large companies used to model business processes) handles conditions and branching.
But my personnal experience is that linear flows work really well in the context of apps with just those two additions :
The ability to cancel a running flow. The ability for a step to « do nothing » if the conditions for its execution aren’t met.
Re: Managing State with Signals
#25Elm started as a FRP language and ended up giving up FRP[1] for ease of use.
If ease of use is targeted, signals might not be the best approach. I distinctly remember things becoming easier when they went away.
Re: Managing State with Signals
#26It's interesting how every build system, frontend framework, programming language implements its own promise pipeline/delayed execution/observables/event propagation. But the implementations are rarely extracted out for general purpose usage and rarely have a rich API. I've been thinking a lot about a general purpose "epoll" which be registered on objects that change. I want to be able to register a reaction to a seq…
> But the implementations are rarely extracted out for general purpose usage and rarely have a rich API.
SolidJS pitches its state management as being robust enough for use outside of itself.
IMO, most state management tools baked into ui frameworks aren’t robust enough to be worth extracting.
Re: Managing State with Signals
#27It's interesting how every build system, frontend framework, programming language implements its own promise pipeline/delayed execution/observables/event propagation. But the implementations are rarely extracted out for general purpose usage and rarely have a rich API. I've been thinking a lot about a general purpose "epoll" which be registered on objects that change. I want to be able to register a reaction to a seq…
I too loved Knockout's observable model - I've found Mobx a worth successor. As it's entirely independent of any framework it is very practical for general purpose usage. I use it for reactive state with both React and in backend Node code with no problems.
Re: Managing State with Signals
#28The observable syntax is confusing. Lisp uses *earmuffs* syntax for global variables, if you only use one muff for an observable variable, how would you express a global variable that's observable? Using **lopsided muffs*?
Re: Managing State with Signals
#29It looks like we are going to keep reinventing dataflow constraints[1] over and over again, always with slightly different terminology (Rx, FRP, signals, ...) So it (a) appears to be a very useful or at least attractive concept, and (b) somehow difficult to fit into current programming languages/practice in a clean way. [1] https://blog.metaobject.com/2014/03/the-siren-call-of-kvo-an... (HN: https://news.ycombinator.…
I feel like reactive programming is approaching ripeness for a mainstream programming language or cross-stack paradigm within the next few years. React, Svelte, Redux etc in the frontend world has certainly paved the way on the mainstream side, albeit in a simplified environment (singlethreaded, does not cross the network boundary and can simply share memory cheaply). I wonder if a refined version of this with will p…
What's the difference between reactive and functional programming? Both seem to focus on expressing relationships between objects and having compiler/runtime infer the computation, instead of explicitly specifying the computation.
Re: Managing State with Signals
#30It looks like we are going to keep reinventing dataflow constraints[1] over and over again, always with slightly different terminology (Rx, FRP, signals, ...) So it (a) appears to be a very useful or at least attractive concept, and (b) somehow difficult to fit into current programming languages/practice in a clean way. [1] https://blog.metaobject.com/2014/03/the-siren-call-of-kvo-an... (HN: https://news.ycombinator.…
I feel like reactive programming is approaching ripeness for a mainstream programming language or cross-stack paradigm within the next few years. React, Svelte, Redux etc in the frontend world has certainly paved the way on the mainstream side, albeit in a simplified environment (singlethreaded, does not cross the network boundary and can simply share memory cheaply). I wonder if a refined version of this with will p…
Elm was positioned to be this. Still technically could be, but adoption isn’t high. Original Elm had signals.