Really cool project. To be honest, I think I don't fully understand the concept of a content addressed language. Initially I thought this was another BEAM language, but it seems to run on its own VM. How does Unison compare to BEAM languages when it comes to fault tolerance? What do you think is a use case that Unison shines that Erlang maybe falls short?

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pchiusano 4 hours ago | parent [-]

Erlang is great and was one inspiration for Unison. And a long time ago, I got a chance to show Joe Armstrong an early version of Unison. He liked the idea and was very encouraging. I remember that meant a lot to me at the time since he's a hero of mine. He had actually had the same idea of identifying individual functions via hashes and had pondered if a future version of Erlang could make use of that. We had a fun chat and he told me many old war stories from the early days of Erlang. I was really grateful for that. RIP, Joe.

Re: distributed computing, the main thing that the content-adressed code buys you is the ability to move computations around at runtime, deploying any missing dependencies on the fly. I can send you the expression `factorial 4` and what I'm actually sending is a bytecode tree with a hash of the factorial function. You then look this up in your local code cache - if you already have it, then you're good to go, if not, you ask me to send the code for that hash and I send it and you cache it for next time.

The upshot of this is that you can have programs that just transparently deploy themselves as they execute across a cluster of machines, with no setup needed in advance. This is a really powerful building block for creating distributed systems.

In Erlang, you can send a message to a remote actor, but it's not really advisable to send a message that is or contains a function since you don't know if the recipient has that function's implementation. Of course, you can set up an Erlang cluster so everyone has the same implementation (analogous to setting up a Spark cluster to have the same version of all dependencies everywhere), but this involves setup in advance and it can get pretty fragile as you start thinking about how these dependencies will evolve over time.

A lot of Erlang's ideas around fault tolerance carry over to Unison as well, though they play out differently due to differences in the core language and libraries.

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shay_ker 2 hours ago | parent [-]

Very dumb question - sending code over the network to be executed elsewhere feels like a security risk to me?

I’m also curious how this looks with browser or mobile clients. Surely they’re not sending code to the server?

	▲	pchiusano 2 hours ago \| parent \| next [-]
		Mobile or browser clients talk to a Unison backend services over HTTP, similar to any other language. Nothing fancy there.[1] > sending code over the network to be executed elsewhere feels like a security risk to me? I left out many details in my explanation and was just describing the core code syncing capability the language gives you. You can take a look at [2] to see what the core language primitives are - you can serialize values and code, ask their dependencies, deserialize them, and load them dynamically. To turn that into a more industrial strength distributed computing platform, there are more pieces to it. For instance, you don't want to accept computations from anyone on the internet, only people who are authenticated. And you want sandboxing that lets you restrict the set of operations that dynamically loaded computations can use. Within an app backend / deployed service, it is very useful to be able to fork computations onto other nodes and have that just work. But you likely won't directly expose this capability to the outside world, you instead expose services with a more limited API and which can only be used in safe ways. [1] Though we might support Unison compiling to the browser and there have already been efforts in that direction - https://share.unison-lang.org/@dfreeman/warp This would allow a Unison front end and back end to talk very seamlessly, without manual serialization or networking [2] https://share.unison-lang.org/@unison/base/code/releases/7.4...
	▲	rlmark an hour ago \| parent \| prev [-]
		Not a dumb question at all! Unison's type system uses Abilities (algebraic effects) for functional effect management. On a type level, that means we can prevent effects like "run arbitrary IO" on a distributed runtime. Things that run on shared infrastructure can be "sandboxed" and prevented with type safety. The browser or mobile apps cannot execute arbitrary code on the server. Those would typically call regular Unison services in a standard API.