[scott_s]

When I call a function, I have no way of knowing if there are any unhandled promises within it. The difference is the restriction: with nurseries, background tasks can only outlive function calls if the calling function allows them to.

[jeremiep]

I get compile-time warnings or runtime errors when I create unhandled promises. What more is needed?

[scott_s]

Needed is a strong word, but what this provides are guarantees when reading the code. Much like you know that control flow will come back to the function you're reading after calling another function. We didn't need to know that control flow will resume in the calling function, but it turned out to be very useful.

[jeremiep]

What guarantees? Nothing prevents a function receiving a nursery from not using it. Unless the language can enforce it you don't really gain anything valuable over returning a Promise, except more complex code that doesn't compose.

> Much like you know that control flow will come back to the function you're reading after calling another function.

What about continuations? Exceptions? Aborts? setjmp()? I can think of many cases where control doesn't return to the caller that are perfectly valid.

Basically, either the code is so simple theres obviously no bugs, or the code is so complex theres no obvious bugs. I feel a nursery is closer to the later than the former.

[yoz-y]

Can you force explicit nursery passing though? One might make a global nursery object and then just rely on that.

[scott_s]

In some existing languages, yes. But it’s easy to imagine future languages (including future versions of current languages) that disallow creating nurseries outside of a function scope.

[jeremiep]

At this point you're pretty much reinventing Monads.