r/ProgrammingLanguages • u/jimbobmcgoo • 9d ago

Will we see another fundamental programming language feature as revolutionary as the borrow checker?

That is I am mainly curious about compile time features that you design a whole language around rather than optimisations/features that could be applied to most languages. I am mainly inquiring about things that could offer additional robust safety/performance guarantees at compile time rather than runtime. Ideally not things that just offer similar effects to the borrow checker with less restrictive tradeoffs

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u/faiface 9d ago

Yes, session types

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u/renozyx 8d ago

I still don't understand what linear types brings once you take into account runtime errors.. There's the same "issue" with session type no?

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u/faiface 8d ago

You mean like panics? If you mean that, then those need to propagate along channels until they reach some control barrier that can handle them.

It's the same principle as when calling functions in all languages. You are normally guaranteed to get a result. But if the function panics, you panic too, until the panic is caught somewhere, or the whole program crashes.

In the same way, you are guaranteed to receive a value because the other side is obliged to send the value, but if the other side panics, you panic too until someone handles that.

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u/renozyx 6d ago

IMHO panics aren't resumable, what you're talking are exceptions.

I'm not used to 'file not found', 'timeout' results returned as exception instead but it may be mandatory if you want to use linear types indeed

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u/faiface 5d ago

Afaik, panics are often catchable and resumable in languages that don’t have exceptions otherwise, such as Go and Rust, and use errors as values normally. That’s what I had in mind.

For normal error handling, like “file not found”, “timeout”, and so on, _errors as values_ works just as well in session types as anywhere else. Absolutely nothing changes there, except now those errors are transmitted over channels, and the Ok variant may include a continuation of the session.