Someone once told me “continuations are isomorphic to monads” and I eventually realized that the best way to do something monad-like in JS was to write function

Someone once told me “continuations are isomorphic to monads” and I eventually realized that the best way to do something monad-like in JS was to write functions that take a callback as their last argument and then higher order functions that manage threading the callbacks around, occasionally transforming it to slot in impure behaviors. I really disagree with the notion “HKT are necessary for monads”, though: they’re necessary to statically check that your monadic code is correct, but asside from things that rely on return-type inference, you can just implement those type-checks as runtime checks (or leave them out entirely): if the architecture of side-effects in your app is arranged around monadic principles, you can write all the same generic transformations (and, in fact, designing your dynamically typed code this way can get you a good fraction of the correctness benefits of static typechecking)