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by tyoverby 3277 days ago
The page that you linked to shows off some features that are not really found in any major programming langauge. Time-traveling search is a big one for me.

Many languages have exceptions, but with shift/reset, you can implement your own exception handling behavior trivially, including things like resumable exceptions.

Some languages have async/await, but almost all of those implementations are state-machine based, which means that they don't compose well when used with more complex language features like generics and higher order functions.

But more than that, in continuation-based asynchronous programming, "async" functions are just normal functions that execute in an async prompt. Here's an example of a multi-user asynchronous TCP echo server in my toy language with tagged delimited continuations:

    async {
      loop {
        let conn = accept_connection("localhost", 9999)
        async {
          loop {
            let data = conn.next_data()
            conn.send(data)
          }
        }
      }
    }
Where all of those asyncrhonous constructs (including `async` itself) are really short wrappers around delimited continuation machinery.

You'll notice that the nested calls to `async` indicate that there are two asyncrhonous contexts

1. Connection acceptance happen on their own "thread" of control

2. Each connection gets their own context in which everything is internally asyncrhonous

1 comments

time-travelling search can be done with recursion. Otherwise, i agree that they don't compose well with each other in some languages. However, it is harder to implement efficiently as far as i understand; time will tell if they are widely understood to be implemented in future languages.