One of the things I find most exciting about effect systems is that they solve some of the issues with typeclasses and traits. The issue with these is you can provide exactly one implementation for a type, and this implementation then applies to your entire program. (The underlying theoretical issue, I guess, is coherence.) This means that code cannot request injection of behaviour _except_ through the type of its data.
In practice, what that means is you get a strong temptation to hang behaviour on data even when it doesn't fit perfectly. Because of the natural desire to reduce the number of entity definitions, you end up defining a typeclass on a data type that doesn't fit exactly just to get the behaviour to the right place without having to introduce a new policy or something.
Effects change this by essentially letting you provide multiple names implementations for the same data type, and you don't need to pass around a policy type because the polymorphism lets you tie handlers to scope.
So, if the fancy type-safe library-based control flow doesn't really do much for you, I think that their potential for code design is a good reason to still be excited!
For the most part, this article discusses just plain effects, ie. "resumable exceptions". Algebraic effects are about the composition (ie. algebra) of effects, exactly like algebraic data types are about the composition of types. This part is generally not meaningful in an untyped language like Javascript because effects are all YOLO and you never know what’s going to happen, what effects a function might throw, or whether there’s any handler up-stack to catch your effect.
I submitted this because I've been getting really interested in effect systems, especially now that OCaml 5 has a working production quality example they'd been iterating on for years prior. I wanted to see what it'd look like in Rust too so maybe one day we can get rid of async function coloring, and with OxCaml by Jane Street maybe we could see how that would look in practice.
Another reason for submitting this is that React actually has a quite robust effect system, that people don't necessarily realize they're using one every day if they use hooks.
I was completely baffled by "algebraic effects" for years. They looked far too confusing for me to want to spend my time on them, and took the "Don’t feel like you have to [get curious about them]" approach.
But then at some point it struck me: underlying all these effect systems is just passing stuff in. So I developed my own effect system for Haskell, Bluefin[1], based on capabilities, which means the "capability to perform some effect" is represented by just passing stuff in (that is, a function can do some effect as long as it has been passed the capability to do it).
From this point of view it's hard to understand the excitement over "resume with" and "the part you can’t do with try / catch. It lets us jump back to where we performed the effect, and pass something back to it from the handler". Programming languages have had that feature since forever: a "resumable exception" is a "function call". A dynamically chosen "resumable exception" is the call of a dynamically chosen function, i.e. the argument to a higher order function.
So I don't know why people love the complexity around "algebraic effects". Maybe the mystique has a certain allure. But if you want the most straightforward possible approach I can recommend you try out Bluefin. I'm happy to answer questions on the issue tracker[2].
(Caveat: Bluefin is able to simplify things dramatically by dropping support for "multi-shot" continuations. But mostly you don't want multi-shot continuations.)
A real effect system allows you to do things like NOT continue execution after using the effect (like the error effect does - if you "implement" this by using Exceptions, you're not using effects at all, just using Exceptions with extra steps) or only continuing it after some asynchronous work happens (the Future effect), or even "continue" execution several times. That just cannot be done with "just passing stuff in". You still don't seem to have understood effects.
Equating "algebraic effects" with "continuations" is like saying "if" is just "goto" (which isn't even true, e.g., an if can turn into a cmov or whatever).
The only mystique around algebraic effects is the same mystique there is around monads. I don't know if people have started equating algebraic effects to burritos yet but that's a pretty good way to take something simple and turn it into something confusing.
> Equating "algebraic effects" with "continuations" is like saying "if" is just "goto"
Fair enough. But are you responding to something I said? I didn't make that equation.
> The only mystique around algebraic effects is the same mystique there is around monads. I don't know if people have started equating algebraic effects to burritos yet but that's a pretty good way to take something simple and turn it into something confusing.
Ah, are you saying that fundamentally there isn't really much to algebraic effects and they're much simpler than they're made out to be? If so then it perhaps we agree?
So this looks like dynamically scoped callbacks. Instead of passing callbacks along as parameters they are declared as “handlers”, and any function down the call stack can invoke them. Is this a correct understanding?
That's what I was thinking. You could get almost all of this pretty directly in Javascript by putting a callback function in an AsyncLocalStorage instance or, in other languages, in a thread local variable.
Yes, this article is doing a bad job at explaining why you would want effects, and one of the main advantages is exactly that it becomes part of the type system, essentially coloring every single function with a set of effects it needs to be called. As the article used JavaScript it shows what untyped effects would look like, which in my opinion is awful.
If you want to use algebraic effects today, I highly recommend Unison. If you’re on the JVM, Flix is doing major advances with effects!
When you need to use an effect, you need it in the type. If you directly call a function using some other effect, it propagates into your function. So far, so colourful.
But you can have generic effects. Your arguments and return type can specify "any effect", indicating your function can use a type with any effect safely, or can be used in any effect context safely.
Passing an async value to a function doesn't mean that function must now also be an async function. It can be a "for all effects, do the thing" function. The code duplication problem is gone.
No, they are function colouring. That's the point.
Someone writes a post lamenting red and blue functions, and everyone eats it up.
Substitute colour for something meaningful and the idea becomes idiotic.
"Top level function declares that it is non-blocking, but when I try to call a small blocking function from it, I have to change the declaration to blocking???"
How do you handle logging then? If f() calls g(), how can I add logging to g() without having to change or recompile f() (and everything in the call stack above it)? ‘You can’t’ is not an acceptable answer.
I swear I'm not trying to be inflamatory, but this is the _worst_ programming language feature I could ever imagine. I'm not trying to be hyperbolic, if I try to reason about it there is nothing I can come up with that I would dislike more in the realm of recent features that have been pitched in the PL community
I was already in the camp that try/catch is "considered harmful", I dislike the concept of having a second, hidden, control flow that might get sprung up upon function callers, because it has side effects buried in the implementation of a callee that are not defined in the parameters or the returns, and I am not 100% sold on the benefits of "Things in the middle don’t need to concern themselves with error handling.", which I guess informs this opinion.
Now since I hate that, I really, really would hate that on top of this, another programmer could write a hidden control flow upstairs that could, potentially, not just crash my code, but also do a lot of other things, such as coming up with default values for unexpected NULLs or whatever, which could THEN take something that would have crashed immediately, and turn it into something that crashes later down the line, away from the problem, with a varialble set to an inexplicable value that I have never put there myself
Because you must statically declare dependency on an effect, it's opt-in.
To be clear, you still pay indirection cost: when you do opt in you have to hope the upstairs implementation is compliant to the contract. But that does also apply to interfaces/typeclasses.
I’ve used effects in scala3 with cats-effects and haven’t been impressed. All in all, the way it was used was just to reimplement a very similar interface to exceptions.
Cats Effect is monadic effects. What is discussed here is sometimes called "direct-style" effects, and is an alternative representation.
I think you've missed the point regarding effect systems. Concurrency and resource handling, implemented in a way that is composable and reasonably easy to reason about, are two of the big ticket features.
Everything he lists is solved by effect-ts [1] bar, obviously, the language support (effect has its own fiber-based runtime like ZIO's scala).
I've been using it for 5+ years and my 4 men team can scale to supporting 6 different products (each running millions $ in business, sometimes daily), as we reuse the same patterns and architecture. This would not be possible without Effect, even though I'm lucky to have terrific engineers as colleagues, we just wouldn't be able to without the endless goodies from Effect.
The amount of features is basically endless, as effects and runtimes weren't enough, from SQL to AI, from effectful schemas (encoders/decoders), first-class OTEL support, CLI, debuggers, editor extensions, and many others. There's still countless modules I have yet to see or use.
Runtimes are available for each platform, including cloudflare workers.
There's absolutely nothing in TypeScript land to have such a wide scope.
v4 will also bring durable workflows (I'm already using v4 beta and that feature in prod) and many other goodies. That's quite important for us needing to have procedures that need to survive redeploys, crashes, etc.
I would never go back to writing standard TypeScript.
There is a learning curve, but you can adopt it incrementally. Nobody adopting it has ever gone back.
That being said, it would be great if there was a proper effect-based language (I've seen few projects like Effekt, but there's way too many things missing) as TypeScript is verbose, and effect adds its own verbosity.
Effect is pretty nice, I'm not sure how worth it it is for the frontend, but I've heard good things on the backend, but sadly I don't use TypeScript for backend work, mainly Rust, and would love to see something like that there. I'm not sure how much Rust's type system would make it possible though however.
I know parts of Effect like its schema are incrementally adoptable but if you use it substantially with many of its features, isn't it viral in a sense? In that you need to do things the Effect way and wrap libraries into Effect functions?
It does tend to naturally bubble upwards as you point out, but you can decide where to stop.
E.g. you could describe a complex effect that has retry, scheduling, etc and run it only once with `Effect.runFork(yourEffect)` in a random place of your existing code.
That's in general how teams adopt it, in general there's a champion in the team that sells using one feature, and as people get accustomed and the champion does a good work mentoring it slowly takes over whole projects.
The learning curve is quite steep but once you get it you become effect pilled. You can completely separate the WHAT the application does from HOW it will do it.
In practice, what that means is you get a strong temptation to hang behaviour on data even when it doesn't fit perfectly. Because of the natural desire to reduce the number of entity definitions, you end up defining a typeclass on a data type that doesn't fit exactly just to get the behaviour to the right place without having to introduce a new policy or something.
Effects change this by essentially letting you provide multiple names implementations for the same data type, and you don't need to pass around a policy type because the polymorphism lets you tie handlers to scope.
So, if the fancy type-safe library-based control flow doesn't really do much for you, I think that their potential for code design is a good reason to still be excited!
For the most part, this article discusses just plain effects, ie. "resumable exceptions". Algebraic effects are about the composition (ie. algebra) of effects, exactly like algebraic data types are about the composition of types. This part is generally not meaningful in an untyped language like Javascript because effects are all YOLO and you never know what’s going to happen, what effects a function might throw, or whether there’s any handler up-stack to catch your effect.
I submitted this because I've been getting really interested in effect systems, especially now that OCaml 5 has a working production quality example they'd been iterating on for years prior. I wanted to see what it'd look like in Rust too so maybe one day we can get rid of async function coloring, and with OxCaml by Jane Street maybe we could see how that would look in practice.
Another reason for submitting this is that React actually has a quite robust effect system, that people don't necessarily realize they're using one every day if they use hooks.
But then at some point it struck me: underlying all these effect systems is just passing stuff in. So I developed my own effect system for Haskell, Bluefin[1], based on capabilities, which means the "capability to perform some effect" is represented by just passing stuff in (that is, a function can do some effect as long as it has been passed the capability to do it).
From this point of view it's hard to understand the excitement over "resume with" and "the part you can’t do with try / catch. It lets us jump back to where we performed the effect, and pass something back to it from the handler". Programming languages have had that feature since forever: a "resumable exception" is a "function call". A dynamically chosen "resumable exception" is the call of a dynamically chosen function, i.e. the argument to a higher order function.
So I don't know why people love the complexity around "algebraic effects". Maybe the mystique has a certain allure. But if you want the most straightforward possible approach I can recommend you try out Bluefin. I'm happy to answer questions on the issue tracker[2].
(Caveat: Bluefin is able to simplify things dramatically by dropping support for "multi-shot" continuations. But mostly you don't want multi-shot continuations.)
EDIT: I was too pessimistic, bazoom42 has noticed this :) https://news.ycombinator.com/item?id=48334067
[1] https://hackage.haskell.org/package/bluefin
[2] https://github.com/tomjaguarpaw/bluefin/issues/new
The only mystique around algebraic effects is the same mystique there is around monads. I don't know if people have started equating algebraic effects to burritos yet but that's a pretty good way to take something simple and turn it into something confusing.
Fair enough. But are you responding to something I said? I didn't make that equation.
> The only mystique around algebraic effects is the same mystique there is around monads. I don't know if people have started equating algebraic effects to burritos yet but that's a pretty good way to take something simple and turn it into something confusing.
Ah, are you saying that fundamentally there isn't really much to algebraic effects and they're much simpler than they're made out to be? If so then it perhaps we agree?
https://lisp-docs.github.io/cl-language-reference/chap-9/j-b...
But while the condition system can do many things you can also do with effects, they cannot do everything.
Here's another discussion on this: https://news.ycombinator.com/item?id=44078743
No ASM involved so technically portable (although it depends on built-in).
Flix equivalent (copy paste to https://play.flix.dev/):
https://www.unison-lang.org/
https://flix.dev/
But you can have generic effects. Your arguments and return type can specify "any effect", indicating your function can use a type with any effect safely, or can be used in any effect context safely.
Passing an async value to a function doesn't mean that function must now also be an async function. It can be a "for all effects, do the thing" function. The code duplication problem is gone.
Someone writes a post lamenting red and blue functions, and everyone eats it up.
Substitute colour for something meaningful and the idea becomes idiotic.
"Top level function declares that it is non-blocking, but when I try to call a small blocking function from it, I have to change the declaration to blocking???"
Yes, yes you do.
Total functions can't call non-total functions.
Deterministic functions can't call nondeterministic functions.
Non-IO functions can't call IO functions.
How do you handle logging then? If f() calls g(), how can I add logging to g() without having to change or recompile f() (and everything in the call stack above it)? ‘You can’t’ is not an acceptable answer.
I was already in the camp that try/catch is "considered harmful", I dislike the concept of having a second, hidden, control flow that might get sprung up upon function callers, because it has side effects buried in the implementation of a callee that are not defined in the parameters or the returns, and I am not 100% sold on the benefits of "Things in the middle don’t need to concern themselves with error handling.", which I guess informs this opinion.
Now since I hate that, I really, really would hate that on top of this, another programmer could write a hidden control flow upstairs that could, potentially, not just crash my code, but also do a lot of other things, such as coming up with default values for unexpected NULLs or whatever, which could THEN take something that would have crashed immediately, and turn it into something that crashes later down the line, away from the problem, with a varialble set to an inexplicable value that I have never put there myself
What a nightmare to debug! I mean, come on
To be clear, you still pay indirection cost: when you do opt in you have to hope the upstairs implementation is compliant to the contract. But that does also apply to interfaces/typeclasses.
I think you've missed the point regarding effect systems. Concurrency and resource handling, implemented in a way that is composable and reasonably easy to reason about, are two of the big ticket features.
I've been using it for 5+ years and my 4 men team can scale to supporting 6 different products (each running millions $ in business, sometimes daily), as we reuse the same patterns and architecture. This would not be possible without Effect, even though I'm lucky to have terrific engineers as colleagues, we just wouldn't be able to without the endless goodies from Effect.
The amount of features is basically endless, as effects and runtimes weren't enough, from SQL to AI, from effectful schemas (encoders/decoders), first-class OTEL support, CLI, debuggers, editor extensions, and many others. There's still countless modules I have yet to see or use.
Runtimes are available for each platform, including cloudflare workers.
There's absolutely nothing in TypeScript land to have such a wide scope.
v4 will also bring durable workflows (I'm already using v4 beta and that feature in prod) and many other goodies. That's quite important for us needing to have procedures that need to survive redeploys, crashes, etc.
I would never go back to writing standard TypeScript.
There is a learning curve, but you can adopt it incrementally. Nobody adopting it has ever gone back.
That being said, it would be great if there was a proper effect-based language (I've seen few projects like Effekt, but there's way too many things missing) as TypeScript is verbose, and effect adds its own verbosity.
[1] https://effect.website/
I know parts of Effect like its schema are incrementally adoptable but if you use it substantially with many of its features, isn't it viral in a sense? In that you need to do things the Effect way and wrap libraries into Effect functions?
E.g. you could describe a complex effect that has retry, scheduling, etc and run it only once with `Effect.runFork(yourEffect)` in a random place of your existing code.
That's in general how teams adopt it, in general there's a champion in the team that sells using one feature, and as people get accustomed and the champion does a good work mentoring it slowly takes over whole projects.