idk stackless dates back to 2005 at least, most likely earlier.
greenlet which is sort of minimal stackless .. before 2008
pycoev which is on one hand greenlets without memmove()s, on the other hand sort of io-scheduled m:n threading I wrote myself in 2009.
so, at least idk, 20 years?
It was first needed. Then 10 years passed, people got around to pushing it through the process aaand by the time it was done it was already not needed. so it all stalled. Same with Rust.
Nowadays server-side async is handled very differently. And client-side is dominated by that abomination called JS.
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