Document internals

[felixSchl]

It'd be great to have an overview of how the internals were designed, or to point to literature that served as reference - nothing too fancy. I could be totally wrong about this, but it seems like this project has a very low bus factor for being such a crucial library to rely on. The code is fairly complex - albeit neatly written - JS FFI code that relies on mutation of scoped variables and other runtime intricacies. I've ventured into src/Effect/Aff.js numerous times over the last half a year or so and always come out just as smart as I went in. Knowing what it's trying to do while reading the code or even a reference implementation at hand would ease the learning curve quite a bit, i'd hope.

[natefaubion]

As background https://www.youtube.com/watch?v=dbM72ap30TE might help since it goes through the problems Aff is trying to solve and the approach. As far as implementation goes, specific questions would go a long way towards letting me know what is unclear around decisions made.

The main loop where the magic happens (core interpreter).
https://github.com/slamdata/purescript-aff/blob/c02ae17e7da8c4df75b824c5b18911931bfe7eba/src/Effect/Aff.js#L257-L524

Low-level join logic
https://github.com/slamdata/purescript-aff/blob/c02ae17e7da8c4df75b824c5b18911931bfe7eba/src/Effect/Aff.js#L526-L544

Kill logic
https://github.com/slamdata/purescript-aff/blob/c02ae17e7da8c4df75b824c5b18911931bfe7eba/src/Effect/Aff.js#L546-L594

Interface
https://github.com/slamdata/purescript-aff/blob/c02ae17e7da8c4df75b824c5b18911931bfe7eba/src/Effect/Aff.js#L609-L627

ParAff interpreter. This is so complicated because of stack safety. A stack unsafe implementation is trivial.
https://github.com/slamdata/purescript-aff/blob/c02ae17e7da8c4df75b824c5b18911931bfe7eba/src/Effect/Aff.js#L630-L992

If you wanted to attempt a read-through, and note specific questions about these concepts, I would be happy to elaborate.