I remember playing with Alpaca a few years ago, and it was fun though I didn’t find the resulting code to significantly less error-prone than when I wrote regular Erlang. It’s inelegant, but I find that Erlang’s quasi-runtime-typing with pattern matching gets you pretty far and it falls into Erlang’s “let it crash” philosophy nicely.

Honestly, and I realize that this might get me a bit of flack here and that’s obviously fine, but I find type systems start losing utility with distributed applications. Ultimately everything being sent over the wire is just bits. The wire doesn’t care about monads or integers or characters or strings or functors, just 1’s and 0’s, and ultimately I feel like imposing a type system can often get in the way more than it helps. There’s so much weirdness and uncertainty associated with stuff going over the wire, and pretty types often don’t really capture that.

I haven’t tried Gleam yet, and I will give it a go, and it’s entirely possible it will change my opinion on this, so I am willing to have my mind changed.

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sfvisser 3 hours ago | parent | next [-]

I don’t understand this comment, yes everything going over the wire is bits, but both endpoints need to know how to interpret this data, right? Types are a great tool to do this. They can even drive the exact wire protocol, verification of both data and protocol version.

So it’s hard to see how types get in the way instead of being the ultimate toolset for shaping distributed communication protocols.

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tombert 3 hours ago | parent [-]

Bits get lost, if you don’t have protocol verification you get mismatched types.

Types naively used can fall apart pretty easily. Suppose you have some data being sent in three chunks. Suppose you get chunk 1 and chunk 3 but chunk 2 arrives corrupted for whatever reason. What do you do? Do you reject the entire object since it doesn’t conform to the type spec? Maybe you do, maybe you don’t, or maybe you structure the type around it to handle that.

But let’s dissect that last suggestion; suppose I do modify the type to encode that. Suddenly pretty much every field more or less just because Maybe/Optional. Once everything is Optional, you don’t really have a “type” anymore, you have a a runtime check of the type everywhere. This isn’t radically different than regular dynamic typing.

There are more elaborate type systems that do encode these things better like session types, and I should clarify that I don’t think that those get in the way. I just think that stuff like the C type system or HM type systems stop being useful, because these type systems don’t have the best way to encode the non-determinism of distributed stuff.

You can of course ameliorate this somewhat with higher level protocols like HTTP, and once you get to that level types do map pretty well and you should use them. I just have mixed feelings for low-level network stuff.

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eyelidlessness 3 hours ago | parent [-]

> But let’s dissect that last suggestion; suppose I do modify the type to encode that. Suddenly pretty much every field more or less just because Maybe/Optional. Once everything is Optional, you don’t really have a “type” anymore, you have a a runtime check of the type everywhere. This isn’t radically different than regular dynamic typing.

Of course it’s different. You have a type that accurately reflects your domain/data model. Doing that helps to ensure you know to implement the necessary runtime checks, correctly. It can also help you avoid implementing a lot of superfluous runtime checks for conditions you don’t expect to handle (and to treat those conditions as invariant violations instead).

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tombert 2 hours ago | parent [-]

No, it really isn’t that different. If I had a dynamic type system I would have to null check everything. If I have declare everything as a Maybe, I would have to null check everything.

For things that are invariants, that’s also trivial to check against with `if(!isValid(obj)) throw Error`.

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dwb an hour ago | parent | next [-]

Sure. The difference is that with a strong typing system, the compiler makes sure you write those checks. I know you know this, but that’s the confusion in this thread. For me too, I find static type systems give a lot more assurance in this way. Of course it breaks down if you assume the wrong type for the data coming in, but that’s unavoidable. At least you can contain the problem and ensure good error reports.

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the-grump 2 hours ago | parent | prev [-]

You missed the entire point of the strong static typing.

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tombert 2 hours ago | parent [-]

I don’t think I did. I am one of the very few people who have had paying jobs doing Scala, Haskell, and F#. I have also had paying jobs doing Clojure and Erlang: dynamic languages commonly used for distributed apps.

I like HM type systems a lot. I’ve given talks on type systems, I was working on trying to extend type systems to deal with these particular problems in grad school. This isn’t meant to a statements on types entirely. I am arguing that most systems don’t encode for a lot of uncertainty that you find when going over the network.

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the-grump 2 hours ago | parent [-]

With all due respect, you can use all of those languages and their type systems without recognizing their value.

For ensuring bits don't get lost, you use protocols like TCP. For ensuring they don't silently flip on you, you use ECC.

Complaining that static types don't guard you against lost packets and bit flips is missing the point.

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tombert an hour ago | parent [-]

With all due respect, you really do not understand these protocols if you think “just use TCP and ECC” addresses my complaints.

Again, it’s not that I have an issue with static types “not protecting you”, I am saying that you have to encode for this uncertainty regardless of the language you use. The way you typically encode for that uncertainty is to use an algebraic data type like Maybe or Optional. Checking against a Maybe for every field ends up being the same checks you would be doing with a dynamic language.

I don’t really feel the need to list out my full resume, but I do think it is very likely that I understand type systems better than you do.

	▲	folex 12 minutes ago \| parent \| next [-]
		> ends up being the same checks you would be doing with a dynamic language Sure thing. Unless dev forgets to do (some of) these checks, or some code downstream changes and upstream checks become gibberish or insufficient.
	▲	the-grump an hour ago \| parent \| prev [-]
		Fair enough, though I feel so entirely differently that your position baffles me. Gleam is still new to me, but my experience writing parsers in Haskell and handling error cases succinctly through functors was such a pleasant departure from my experiences in languages that lack typeclasses, higher-kinded types, and the abstractions they allow. The program flowed happily through my Eithers until it encountered an error, at which point that was raised with a nice summary. Part of that was GHC extensions though they could easily be translated into boilerplate, and that only had to be done once per class. Gleam will likely never live to that level of programmer joy; what excites me is that it’s trying to bring some of it to BEAM. It’s more than likely your knowledge of type systems far exceeds mine—I’m frankly not the theory type. My love for them comes from having written code both ways, in C, Python, Lisp, and Haskell. Haskell’s types were such a boon, and it’s not the HM inference at all.

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hayleighdotdev 7 minutes ago | parent | prev | next [-]

> Honestly, and I realize that this might get me a bit of flack here and that’s obviously fine, but I find type systems start losing utility with distributed applications. Ultimately everything being sent over the wire is just bits.

Actually Gleam somewhat shares this view, it doesn't pretend that you can do typesafe distributed message passing (and it doesn't fall into the decades-running trap of trying to solve this). Distributed computing in Gleam would involve handling dynamic messages the same way handling any other response from outside the system is done.

This is a bit more boilerplate-y but imo it's preferable to the other two options of pretending its type safe or not existing.

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jakelazaroff 3 hours ago | parent | prev | next [-]

Interesting! I don't share that view at all — I mean, everything running locally is just bits too, right? Your CPU doesn't care about monads or integers or characters or strings or functors either. But ultimately your higher level code does expect data to conform to some invariants, whether you explicitly model them or not.

IMO the right approach is just to parse everything into a known type at the point of ingress, and from there you can just deal with your language's native data structures.

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tombert 3 hours ago | parent [-]

I know everything reduces to bits eventually, but modern CPUs and memory aren’t as “lossy” as the network is, meaning you can make more assumptions about the data being and staying intact (especially if you have ECC).

Once you add distribution you have to encode for the fact that the network is terrible.

You absolutely can parse at ingress, but then there are issues with that. If the data you got is 3/4 good, but one field is corrupted, do you reject everything? Sometimes, but often Probably not, network calls are too expensive, so you encode that into the type with a Maybe. But of course any field could be corrupt so you have to encode lots of fields as Maybes. Suddenly you have reinvented dynamic typing but it’s LARPing as a static type system.

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jakelazaroff 3 hours ago | parent [-]

I think you can avoid most issues by not doing what you're describing! Ensuring data arrives uncorrupted is usually not an application-level concern, and if you use something like TCP you get that functionality for free.

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tombert 2 hours ago | parent [-]

TCP helps but only to a certain extent; it only guarantees specific ordering of bits during its session. Suppose you have to construct an object out of three separate transmissions, like some kind of multipart style thing. If one of the transmissions gets corrupted or gets errors out from TCP, then you still fall into that maybe trap.

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obsoleetorr 2 hours ago | parent [-]

so you need transactions?

I get what your saying, but can't you have the same issue if instead you have 3 local threads that you need to get the objects from, one can throw an exception and you only receive 2, same problem

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tombert 2 hours ago | parent [-]

Sometimes, but I am arguing that you need to encode for this uncertainty if you want to make distributed apps work correctly. If you can do transactions for what you’re doing then great, not every app can do that.

When you have to deal with large amounts of uncertainty, static types often reduce to a bunch of optionals, forcing you to null check every field. This is what you end up having to do with dynamic typing as well.

I don’t think types buy you much in cases with extreme uncertainty, and I think they create noise as a result.

It’s a potentially similar issue with threads as well, especially if you’re not sharing data between them, which has similar issues as a distributed app.

A difference is that it’s much cheaper to do retries within a single process compared to doing it over a network, so if something gets borked locally then a retry is (comparatively) free.

	▲	folex 3 minutes ago \| parent [-]
		> static types often reduce to a bunch of optionals, forcing you to null check every field On one end, you write / generate / assume a deserialisator that checks whether incoming data satisfies all required invariants, eg all fields are present. On the other end, you specify a type that has all the required fields in required format. If deserialisation fails to satisfy type requirements, it produces an error which you can handle by eg falling back to a different type, rejecting operation or re-requesting data. If deserialisation doesn't fail – hooray, now you don't have to worry about uncertainty. The important thing here is that uncertainty is contained in a very specific place. It's an uncertainty barrier, if you wish: before it there's raw data, after it it's either an error or valid data. If you don't have a strict barrier like that – every place in the program has to deal with uncertainty. So it's not necessarily about dynamic / static. It's about being able to set barriers that narrow down uncertainty, and growing number of assumptions. The good thing about ergonomic typing system is that it allows you to offload these assumptions from your mind by encoding them in the types and let compiler worry about it. It's basically automatization of assumptions book keeping.

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phplovesong 29 minutes ago | parent | prev [-]

You seem to have a fundamental misunderstanding about type systems. Most (the best?) typesystems are erased. This means they only have meaning "on compile time", and makes sure your code is sound and preferrably without UB.

The "its only bits" thing makes no sense in the world of types. In the end its machine code, that humans never (in practice) write or read.