fix: use ! for async application

[tonyfettes]

No description provided.

[peter-jerry-ye-code-review]

Async function type signatures are more explicit

Category
Maintainability
Code Snippet
pub fn async_run(f : () -> Unit!Async) -> Unit
Recommendation
The change from async () -> Unit to () -> Unit!Async is good. Keep this pattern consistent throughout the codebase.
Reasoning
The new syntax makes it clearer that async is an effect (like Error) rather than a modifier on the function type. This improves type system clarity and consistency.

Simplified async call syntax

Category
Correctness
Code Snippet
op!!() -> op!()
Recommendation
The change from double bang (!!) to single bang (!) for async calls is good. Continue migrating all async calls to use single bang notation.
Reasoning
The simpler syntax reduces visual noise while maintaining the semantic meaning that this is an async operation. Double bangs could be confused with non-null assertions in other languages.

Consistent error handling with Error effect

Category
Maintainability
Code Snippet
pub fn Promise::unsafe_new[T](op : () -> T!Error + Async) -> Promise
Recommendation
Good change to explicitly specify Error effect. Consider adding documentation explaining the Error+Async effect combination.
Reasoning
Making the Error effect explicit in the type signature helps developers understand potential failure modes and required error handling. The combination with Async effect clearly shows this is an asynchronous operation that may fail.

[rami3l]

@tonyfettes Thanks! However it looks like there is another group of deprecated syntax to be fixed?