alt Hacker NewsHow are the tradeoffs meaningfully different? Imagine that, instead of passing an `Io` object around, you just had to add an `async` keyword to the function, and that was simply syntactic sugar for an implied `Io` argument, and you could use an `await` keyword as syntactic sugar to pass whatever `Io` object the caller has to the callee.
I don't see how that's not the exact same situation.
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VMG • today at 7:53 PM
Maybe I have this wrong, but I believe the difference is that you can create an Io instance in a function that has none
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In the JS example, a synchronous function cannot poll the result of a Promise. This is meaningfully different when implementing loops and streams. Ex, game loop, an animation frame, polling a stream.
A great example is React Suspense. To suspend a component, the render function throws a Promise. To trigger a parent Error Boundary, the render function throws an error. To resume a component, the render function returns a result. React never made the suspense API public because it's a footgun.
If a JS Promise were inspectable, a synchronous render function could poll its result, and suspended components would not need to use throw to try and extend the language.