> Zig actually also had solved the coloring problem in the old and abandondend async-await solution because the compiler simply stamped out a sync- or async-version of the same function based on the calling context (this works because everything is a single compilation unit).

AFAIK this still leaked through function pointers, which were still sync or async (and this was not visible in their type)

> If calling the same function with a different argument would be considered 'function coloring', than every function in a program is 'colored' and the word loses its meaning ;)

Well, yes, but in this case the colors (= effects) are actually important. The implications of passing an effect through a system are nontrivial, which is why some languages choose to promote that effect to syntax (Rust) and others choose to make it a latent invariant (Java, with runtime exceptions). Zig chooses another path not unlike Haskell's IO.

The subject of the function coloring article was callback APIs in Node, so an argument you need to pass to your IO functions is very much in the spirit of colored functions and has the same limitations.

> If calling the same function with a different argument would be considered 'function coloring', than every function in a program is 'colored' and the word loses its meaning ;)

I mean, the concept of "function coloring" in the first place is itself an artificial distinction invented to complain about the incongruent methods of dealing with "do I/O immediately" versus "tell me when the I/O is done"--two methods of I/O that are so very different that it really requires very different designs of your application on top of those I/O methods: in a sync I/O case, I'm going to design my parser to output a DOM because there's little benefit to not doing so; in an async I/O case, I'm instead going to have a streaming API.

I'm still somewhat surprised that "function coloring" has become the default lens to understand the semantics of async, because it's a rather big misdirection from the fundamental tradeoffs of different implementation designs.

If your functions suddenly requires (currently)unconstructable instance "Magic" which you now have to pass in from somewhere top level, that indeed suffers from the same issue as async/await. Aka function coloring.

But most functions don't. They require some POD or float, string or whatever that can be easily and cheaply constructed in place.