5 ms·

That’s all true, but I think a Typescript-like system would work really well here. Typescript is very tolerant of the data being different than the type definit

That’s all true, but I think a Typescript-like system would work really well here. Typescript is very tolerant of the data being different than the type definition, and it doesn’t know or care if your data actually matches the type definition at runtime. It would be up to the developer to account for different versions of the data when writing out type definitions, and the worst case is that you try to access a property that doesn’t exist or is the wrong type, and it crashes and causes the process to get restarted like what already happens in Erlang. So it wouldn’t be a guarantee of correctness just like Typescript isn’t, but it could still offer a lot of safety assuming you get the type definition a right.

derefr 6y ago
I mean, that's already what Erlang/Elixir has, in the form of Dialyzer, a runtime "type linter" (which is what the typespecs in the article feed into.) It's static typing that Erlang can't complete-the-triangle on; not typing generally. The only problem is that "offline" type-checking like this does nothing to solve one of the main use-cases/pain-points where Erlangers want types (or, at least, think they want types): in the messages that actors receive. You can't make any sort of a type assertion about what other actors in the system are allowed to send this actor, and get that validated; because "other actors" in a distributed system necessarily include ones that aren't even part of your present codebase! I have a philosophy about this—not sure where I picked it up, but I think it hews to the Zen of Erlang quite well: If you already know the type of a message, then by definition, it's not a message any more, but just a regular data value. A message is an OOP concept (and Erlang is an OOP language, where processes are the "objects.") An OOP "message" is a piece of data the meaning of which is up to the interpretation of the recipient; where that interpretation can change as the recipient's internal state changes. The whole point of the "receiving a message" code that you write in an Erlang actor-process, is to allow you to do custom logic for that interpreting part. To use the value itself, in making the decision of what the value is. In fact, I would extend that: the whole point of Erlang as a language is to do that "interpreting" part. Once you know what something is and have put it into a canonical validated structure, you may as well hand it off to native code (using e.g. https://github.com/rusterlium/rustler https://github.com/rusterlium/rustler). If you think of native code as being a pure domain of strongly-typed values, then picture Erlang as the glue that lives in the ugly world of "not yet typed" values, making decisions under partial-information conditions on what types to try to conform received messages into, before they can enter that pure strongly-typed domain. That's Erlang's idiomatic use-case! (You can tell, because using it for that produces absolutely beautiful code; whereas using it to do e.g. crypto math, produces an abomination.) Which is all to say: the interpretation (or, if you like, constraint) of a message into a typed value is a Turing-complete operation; and the logic for doing so is best represented as an Erlang program. Erlang doesn't need a type system for messages; Erlang is a type system for messages. :)
- macintux 6y ago
  It’s a bit of a stretch, but your thoughts reminded me of one of Joe Armstrong’s interests, how to document/prove two components were adhering to the protocol they were using to communicate (he was describing the problems of interconnecting two hardware components in the informal talk I attended, but obviously he had a significant interest in software as well). I miss Joe quite a bit. Such a keen mind with seemingly infinite curiosity.
- pmontra 6y ago
  > A message is an OOP concept (and Erlang is an OOP language, where processes are the "objects.") Yes. If only GenServer had an OOP syntax instead of a handle this / handle that list of functions which obfuscate what the process actually does. Elixir in particular lost a chance to make it easier to deal with.
  - dnautics 6y ago
    It's not too late. You can write your own wrapper around the :gen module, and if it's really good maybe people will adopt it. I will say one thing:. If you are thinking of BEAM processes as actors/(Kay objects), you're missing the real meat of what makes BEAM processes special; what they really are are atomic units of failure domains. The other stuff is just a useful analogy that lets people grok the code structure by comparing it to something familiar. The trouble then is that people will take habits from OO and apply them to BEAM where blindly copying the organizational form will lead to performance regressions. If you're treating BEAM processes like python or Java or Ruby objects, you're going to bottleneck your system and turn it into a needlessly complex mess. In short, not all function calls (cheap) should be message passing (expensive). Sorry Alan Kay.
    - pmontra 6y ago
      We have very few GenServers in our system, with their supervisors to keep them alive and read back the initial status from the db in case of failure. They're not object in the Ruby or Python or Java way. They really are servers that take care of a specific action. The vast majority of code is function calls in the main process of the system. Still I'd like to be able to program the GenServer in a more understandable way.

derefr 6y ago

I mean, that's already what Erlang/Elixir has, in the form of Dialyzer, a runtime "type linter" (which is what the typespecs in the article feed into.) It's static typing that Erlang can't complete-the-triangle on; not typing generally. The only problem is that "offline" type-checking like this does nothing to solve one of the main use-cases/pain-points where Erlangers want types (or, at least, think they want types): in the messages that actors receive. You can't make any sort of a type assertion about what other actors in the system are allowed to send this actor, and get that validated; because "other actors" in a distributed system necessarily include ones that aren't even part of your present codebase! I have a philosophy about this—not sure where I picked it up, but I think it hews to the Zen of Erlang quite well: If you already know the type of a message, then by definition, it's not a message any more, but just a regular data value. A message is an OOP concept (and Erlang is an OOP language, where processes are the "objects.") An OOP "message" is a piece of data the meaning of which is up to the interpretation of the recipient; where that interpretation can change as the recipient's internal state changes. The whole point of the "receiving a message" code that you write in an Erlang actor-process, is to allow you to do custom logic for that interpreting part. To use the value itself, in making the decision of what the value is. In fact, I would extend that: the whole point of Erlang as a language is to do that "interpreting" part. Once you know what something is and have put it into a canonical validated structure, you may as well hand it off to native code (using e.g. https://github.com/rusterlium/rustler https://github.com/rusterlium/rustler). If you think of native code as being a pure domain of strongly-typed values, then picture Erlang as the glue that lives in the ugly world of "not yet typed" values, making decisions under partial-information conditions on what types to try to conform received messages into, before they can enter that pure strongly-typed domain. That's Erlang's idiomatic use-case! (You can tell, because using it for that produces absolutely beautiful code; whereas using it to do e.g. crypto math, produces an abomination.) Which is all to say: the interpretation (or, if you like, constraint) of a message into a typed value is a Turing-complete operation; and the logic for doing so is best represented as an Erlang program. Erlang doesn't need a type system for messages; Erlang is a type system for messages. :)

macintux 6y ago
It’s a bit of a stretch, but your thoughts reminded me of one of Joe Armstrong’s interests, how to document/prove two components were adhering to the protocol they were using to communicate (he was describing the problems of interconnecting two hardware components in the informal talk I attended, but obviously he had a significant interest in software as well). I miss Joe quite a bit. Such a keen mind with seemingly infinite curiosity.
pmontra 6y ago
> A message is an OOP concept (and Erlang is an OOP language, where processes are the "objects.") Yes. If only GenServer had an OOP syntax instead of a handle this / handle that list of functions which obfuscate what the process actually does. Elixir in particular lost a chance to make it easier to deal with.
- dnautics 6y ago
  It's not too late. You can write your own wrapper around the :gen module, and if it's really good maybe people will adopt it. I will say one thing:. If you are thinking of BEAM processes as actors/(Kay objects), you're missing the real meat of what makes BEAM processes special; what they really are are atomic units of failure domains. The other stuff is just a useful analogy that lets people grok the code structure by comparing it to something familiar. The trouble then is that people will take habits from OO and apply them to BEAM where blindly copying the organizational form will lead to performance regressions. If you're treating BEAM processes like python or Java or Ruby objects, you're going to bottleneck your system and turn it into a needlessly complex mess. In short, not all function calls (cheap) should be message passing (expensive). Sorry Alan Kay.
  - pmontra 6y ago
    We have very few GenServers in our system, with their supervisors to keep them alive and read back the initial status from the db in case of failure. They're not object in the Ruby or Python or Java way. They really are servers that take care of a specific action. The vast majority of code is function calls in the main process of the system. Still I'd like to be able to program the GenServer in a more understandable way.