Cap'n Web: a new RPC system for browsers and web servers

Post by FungalRaincloud » Tue, Sep 23, 2025, 4:36 PM UTC

dominicrose wrote: post #244

squirrellous wrote: post #180

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Is there anything C# _doesn’t_ have? :-) It feels like C# has an answer to every problem I’ve ever had with other languages - dynamic loading, ADTs with pattern matching, functional programming, whatever this expression tree is, reflection, etc etc. Yet somehow it’s still a niche language that isn't widely used (outside of particular ecosystems).

As someone who dislikes clutter, in my experience it's just easier to read and write with these languages: Perl, PHP, Ruby, Python, Javascript, Smalltalk. If you dare leave the safety of a compiler you'll find that Sublime Merge can still save you when rewriting a whole part of an app. That and manual testing (because automatic testing is also clutter). If you think it's more professional to have a compiler I'd like…

Post by kentonv » Tue, Sep 23, 2025, 5:30 PM UTC

coreload wrote: post #270

kentonv wrote: post #269

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The protocol itself is really only language-specific to a similar extent that JSON is language-specific. Which you can totally argue it is, but also people have figured out how to use it in lots of languages other than JavaScript. I think Cap'n Web could work pretty well in Python and other dynamically-typed languages. Statically-typed would be a bit trickier (again, in the same sense that they are harder to use JSON…

Retrofitting to some but not all languages is not nearly the same as an intentionally language agnostic protocol. To the extent that calling this "web" is at best misleading.

Post by catern » Tue, Sep 23, 2025, 5:38 PM UTC

kentonv wrote: post #255

catern wrote: post #212

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I totally agree with your framing of the value of async/await, but could you elaborate more on why you think that this behavior (which I would call "cooperative concurrency") is important for (ocap?) RPC systems? It seems to me that preemptive concurrency also suffices to make RPC viable. Unless you just feel that preemptive concurrency is too hard, and therefore not workable for RPC systems?

Almost all ocap systems seem to use event loops -- and many of the biggest ocap nerds I know are also the biggest event loop nerds I know. I'm not actually sure if this is a coincidence or if there's something inherent that makes it necessary to pair them. But one thing I can't figure out: What would be the syntax for promise pipelining, if you aren't using promises to start with?

Post by fizx » Tue, Sep 23, 2025, 7:39 PM UTC

kentonv wrote: post #253

fizx wrote: post #213

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Also, your function needs to be very careful on closures. Date.toLocaleString and many other js functions will be different on client and server, which will also cause silent corruption.

If you invoke `Date.toLocaleString()` in a map callback, it will consistently always run on the client.

    client.getAll({userIds}).map((user) => user.updatedAt == new Date().toLocaleString() ? client.photosFor(user.id) : {})

    client.getAll({userIds}).map((user) => client.photos({userId: user.id, since: new Date(user.updatedAt).toLocaleString()})

Post by youngbum » Wed, Sep 24, 2025, 12:46 AM UTC