Suture – Supervisor Trees for Go
jerf.org
jerf.org
A similar effort is happening with the Cloud Haskell program, but my understanding is that they're pouring a lot of effort into transmitting arbitrary Haskell functions over the wire between computers. This is pretty unnecessary for supervision and "Let it Crash"-style error handling alone.
This problem (sync/async) is one of the things that is being solved in this project.
Any reasons to make the switch?
As an example say you have a chat system, you will have a process for each user [0]. If you have a million users, you will end up with a million processes. The supervisor tree watches these processes, so if one crashes a single user may get logged out but everybody else will be unaffected.
[0] In reality you'll probably have it even more fine grained than that, so users will end up with multiple processes.
By sticking with Go, the author gets to keep the static types but likely gets faux-Supervisors at best.
No, seriously, that's really profoundly true. Erlang's definition isn't the only one. But you're free to take it. If you can bend a bit, though, these may not be "faux".
One thing that's easier when it comes to implementing supervisors in not-Erlang though is that the vast majority of languages have something better than "behaviors" to work with, which are bizarrely klunky things. I actually implemented something more like a "gen_server" initially, but it wasn't a win. Some of that "incredible programming" is essential complexity (in Fred Brooks' terminology), but some of it is accidental complexity. Plus Erlang had to build it from true, total scratch; Go is a pre-existing runtime, and "defer" is simple, yet powerful.
It should be pointed out specifically that Erlang's type system is incredibly, annoyingly weak, more so than merely "weak typing". It's a language that doesn't permit any sort of user-created type whatsoever. There are good reasons for this which would be its own interesting blog post, mostly related to the need for a clear serialization for cluster communication, but I think those good reasons have been superceded by later work in the general programming world on serialization of objects and the tradeoff is wrong in 2014. (But, no sarcasm, a good one when it was created. It is no real criticism of a language to observe that it couldn't use lessons learned only a decade after it was created.)
I think you are misusing "object" to mean something like "class" or "type" (the two not really being the same thing except in some statically-typed, class-based, OOPLs); Erlang quite obviously allows user-created objects.
And of course you can use what exists to build "types", such as a dict. But it's still just a record of a certain format rather than a distinct "type"; there's no way in the core system to assert that you have such a "dict", beyond having a record.
If the complaint is just Erlang-lacks-static-typing, I can agree that that's a fact, but I don't see how what Erlang does give you is less useful (even though the particular structure is different) than what you get in other languages that lack static typing.
Well, this gets into quasi-religious debates about type systems. All I can really do is point you to the Python or Ruby class systems and ask you to compare it to Erlang. And also observe that I'm pretty tired of dynamic typing in general, and Erlang is even farther in the direction that I'm tired of than Python/Ruby/etc.
Given two tuples with 3 integers, {X, Y, Z}, without knowing it a priori, you can't tell which one is an erlang:now() and which is an erlang:date().
Even after 7 years of experience, it is very klunky to program in, and in reimplementing the Erlang program I had in hand, I immediately added some features that were very hard to implement in Erlang. And note the architecture of the code didn't actually change, this isn't one of those cases where the second version was also radically different than the first so no comparison is possible, it was actually hard to implement in Erlang. Erlang is a very klunky language to work in. Raw Java might be klunkier, but it's easily the klunkiest of the languages I use.
Erlang's clustering, which my code heavily depends on, just sort of breaks sometimes, on machines that are on the same switch, with every bit of hardware switched out over time. It is very opaque to figure out why it isn't working, or how to make it work again. Mnesia breaks even more often on loads that shouldn't be a problem. After 7 years of working with it, at this point even if the solution was just to turn on this one flag somewhere and all my problems would go away, I still would not consider that a positive.
I don't "hate" it, but I've been waiting for years for a more conventional language that had pervasive microthreading in it that I could use for work. Go is not quite it... I'd still like the goroutines to be completely isolated, and I've got a handful of other quibbles... but it's close enough that I might be able to get out of the hell of trying to multiprocess in most other languages, while being something I might actually be able to get adopted. In general, the company I work for has not been overwhelmed by the effectiveness of Erlang.
In practice, the biggest loss of fundamental capability is loss of true asynchronous exceptions, and, well... in practice that's only an annoyance, not an OH MY GOSH I WILL NEVER USE A LANGUAGE WITHOUT ASYNCHRONOUS EXCEPTIONS sort of thing. In most cases if you're throwing an async exception you've really already lost and now we're just discussing exactly how you're losing.
Every language student should study Erlang, and learn from it, and possibly use it. It's a solid language. And there's nothing wrong with trying to port some of that solidity elsewhere. (I'd pick a real DB over Mnesia, though.)
That is a exceptionally quotable. :)