Comment by conradev
My understanding of this design is that you can write the logic separately from the decision to "do I/O immediately" versus "tell me when the I/O is done"
You can write a parser thats outputs a DOM and run it on a stream, or write a parser with a streaming API and run it synchronously on a buffer. You should pick the optimal tool for the situation, but there is no path dependence anymore.
Honestly I don't see how that is different than how it works in Rust. Synchronous code is a proper subset of asynchronous code. If you have a streaming API then you can have an implementation that works in a synchronous way with no overhead if you want. For example, if you already have the whole buffer in memory sometimes then you can just use it and the stream will work exactly like a loop that you would write in the sync version.