Comment by chmod775
4 days ago
Function coloring also only applies to a few select languages. If your runtime allows you can call an async function from a sync function by pausing execution of the current function/thread whenever you're waiting for some async op.
Libraries like Tokio (mentioned in the article) have support for this built-in. Goroutines sidestep the issue completely. C# Tasks are batteries included in that regard. In fact function colors aren't an issue in most languages that have async/await. JavaScript is the odd one out, mostly due to being single-threaded. Can't really be made to work in a clean way in existing JS engines.
Function coloring is an effect. If the language makes a distinction between sync and async, then it has that effect. Just because there are escape hatches to get around one effect doesn't really change this fact.
Like in Haskell there is the IO monad used to denote the IO effect. And there are unsafe ways to actually execute it - does that make everything in Haskell impure?
“Function coloring” is an imaginary issue in the first place. Or rather it's a real phenomenon, but absolutely not limited to async and people don't seem to care about it at all except when talking about async.
Take Rust: you return `Result<T,E>`, you are coloring your function the same way as you are when using `async`. Same for Option. Errors as return values in Go: again, function coloring.
One of your nested function starts taking a "serverUrl" input parameter instead of reading an environment variable: you've colored your function and you now need to color the entire call stack (taking the url parameter themselves).
All of them are exactly as annoying, as you need to rewrite the entire call stack's function signature to accommodate for the change, but somehow people obsess about async in particular as if it was something special.
It's not special, it's just the reflection that something can either be explicit and require changing many function signatures at once when making a change, or be implicit (with threads, exceptions or global variables) which is less work, but less explicit in the code, and often more brittle.
Function coloring does not mean that functions take parameters and have return values. Result<T,E> is not a color. You can call a function that returns a Result from any other function. Errors as return values do not color a function, they're just return values.
Async functions are colored because they force a change in the rest of the call stack, not just the caller. If you have a function nested ten levels deep and it calls a function that returns a Result, and you change that function to no longer return a result because it lost all its error cases, you only have to change the direct callers. If you are ten layers deep in a stack of synchronous functions and suddenly need to make an asynchronous call, the type signature of every individual function in the stack has to change.
You might say "well, if I'm ten layers deep in stack of functions that don't return errors and have to make a call that returns the error, well now I have to change the entire stack of functions to return the error", but that's not true. The type change from sync to async is forced. The error is not. You could just discard it. You could handle it somehow in one of the intervening calls and terminate the propagation of the type signature changes half way up. The caller might log the error and then fail to propogate it upwards for any number of reasons. You aren't being forced to this change by the type system. You may be forced to change by the rest of the software engineering situation, but that's not a "color".
For similar reasons, the article is incorrect about Go's "context.Context" being a coloration. It's just a function parameter like anything else. If you're ten layers deep into non-Context-using code and you need to call a function that takes a context, you can just pass it one with context.Background() that does nothing context-relevant. You may, for other software engineering reasons, choose to poke that use of a context up the stack to the rest of the functions. It's probably a good idea. But you're not being forced to by the type system.
"Coloration" is when you have a change to a function that doesn't just change the way it interacts with the functions that directly call it. It's when the changes forcibly propagate up the entire call stack. Not just when it may be a good idea for other reasons but when the language forces the changes.
It is not, in the maximally general sense, limited to async. It's just that sync/async is the only such color that most languages in common use expose.
> If you are ten layers deep in a stack of synchronous functions and suddenly need to make an asynchronous call, the type signature of every individual function in the stack has to change.
well, this isn't really true - at least for Rust:
runtime.block_on(async{});
https://docs.rs/tokio/latest/tokio/runtime/struct.Handle.htm...
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If you are ten nested functions deep in sync code and want to call an async function you could always choose to block the thread to do it, which stops the async color from propagating up the stack. That's kind of a terrible way to do it, but it's sort of the analog of ignoring errors when that innermost function becomes fallible.
So I don't buy that async colors are fundamentally different.
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You can exit an async/IO monad just like you can exit an error monad: you have a thread blocking run(task) that actually executes everything until the future resolves. Some runtimes have separate blocking threadpools so you don't stall other tasks.
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You are stuck in a fixed pattern of thinking where async==color. Here's the meme origin: https://journal.stuffwithstuff.com/2015/02/01/what-color-is-...
Here's the list of requirements: 1. Every function has a color. 2. The way you call a function depends on its color. 3. You can only call a red function from within another red function. 4. Red functions are more painful to call. 5. Some core library functions are red.
You are complaining about point 3. You are saying if there's any way to call a red function from a blue function then it's not real. The type change from sync to async is not forced any more than changing T to Result<T,E>. You just get a Promise from the async function. So you logically think that async is not a color. You think even a Haskell IO-value can be used in a pure function if you don't actually do the IO or if you use unsafePerformIO. This is nonsense. Anything that makes the function hard to use can be color.
Returning errors isn't function coloring, it's fundamental language design choice by go.
You can still use a function that returns result in a function that uses option.
And result and option usually mean something else. Option is a value or none. None doesn't necessarily means the function failed. Result is the value or an error message. You can have result<option, error>
That's different then async where you can call the other type.
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