Could you, or anyone else, recommend some well written and idiomatic elixir code that's free to browse through?
Coming from an object oriented background the idea that classless code could be less complex is sorta blowing my mind!
Coming from an object oriented background the idea that classless code could be less complex is sorta blowing my mind!
You can call into a module with a variable, but it's rarely done, outside of some specific types of code interaction (ex: structural event loop processing like gen_server takes a Module to callback into).
Of course, when sending messages to processes, there's not really anything in code to indicate where those will be processed, and I don't know that IDEs help there either. Usually, code organization helps, but it's not required.
Caveat: my experience is with Erlang, not Elixir, but should generally apply.
Not to mention, there's not much boilerplate to deal with and we've got useful control structures like the very readable `cond`s instead of if {} else if { } blocks (Although you can use these, it is generally discouraged in Elixir). I will tell you that being pushed towards writing "cond" s and "when"s, "with"s has guided me towards achieving a better and more readily understood codebase.
In Erlang, the few simplifications you get are very local (as long as you don't apply a parse_transform on your whole project, which is rarely a good idea).
I never wrote a macro in Elixir (only for experimenting with them), nobody ever did in the projects I worked on and I'm perfectly happy with that. On the other side everybody uses macros, mainly with/do/else. I wish they implemented it as keywords of the language. They could probably have spared us the annoyance of converting code from = to <- and comma everytime it is moved inside a with and viceversa. That's the part of the syntax that I like less.
- I'll say that Phoenix Macros somewhat annoy me, but i can see why they would be useful for someone with a Rails background (which I am not).
- I'm quite happy with not having to think about how Ecto marshals its queries into SQL. Life's too short for that.
- Is it really such an impediment to code grokking to have a `test "label" do...end` construct?
I've dug into Ecto, Ecto SQL, Elixir itself at times. This was just because I was trying to figure out some corner-case behavior. The overhead of understanding someone else's classes when I tried similar things in Python was always just a much heavier mental load. Idiomatic or not.
As mentioned by another comment, the important thing is that each function you need to read can pretty much be read on its own. You might need to follow a few trails. But the way a library can hide where the magical state comes from in a Python class is sometimes maddening. I know, because I've written that code.
I find Elixir incredibly readable, nicely writable and the mental overhead continuously lower.
I've written a project that uses macros heavily as well and it's hard to make it easy to understand.
It's a double-edged sword. Macros are nice and can simplify the top-level API significantly, but at the same time they add complexity under the hood.
I like them for use in some bigger frameworks but overall, they seem to provide negative value to me as a reader, often confusing names doing some magical coating which could very well be solved with pure function composition.
I have noticed some python projects making heavy use of it... they rely on you to read their guide to write code instead of switching and using the project fine because you know the language. Sort of like another DSL?
Elixir hits the balance for me between being not too intense (haskell) and friendly usable with a nice community.
https://pragprog.com/book/jgotp/designing-elixir-systems-wit...
It was hugely helpful to me in wrapping my head around something bigger than hello world.
One hurdle that was difficult for me was understanding Behaviors (which are an abstraction used in both Erlang and Elixir). On the one hand, a Behavior is much like an class/object: it has public methods, internal state, polymorphism (via message passing) and to some extent a notion of inheritance. According to Alan Kay, it's more Object-Oriented than Smalltalk!
However, a Behavior runs in it's own process. Like a typical class, public and private functions are defined in the same file This makes reading the code where a Behavior is defined more difficult because the public methods are executing in the client process, but the callbacks (i.e. private functions) are executing in the Behavior's own process.
One insight I gained from working with Erlang was that the "academic" notion of OOP modeling (i.e. model the entities of your domain as discrete objects) works much better with Erlang's proceses/Behaviors than it ever did with classes/objects in languages like Java.
Objects in languages like Java, C#, Ruby, JS, etc. are much at modeling the architectural components of a system, than at actually modeling domain entities directly. That's actually partly why I really the Pony language: it combines both objects as processes (called Actors) and objects as components/capabilities (called Objects).
This doesn't sound right; a behaviour is just a set of functions to be implemented in a 'callback module'; you seem to be talking about processes and modules. I agree with your points though.
Going back, I see that you are right: the Behavior is technically the common pattern that is shared across specific processes. Is there a name for a process that is defined in a callback module?
And really, this complaint about confusing modules spans to more than just callback modules. Most processes define both the client and server functions in the same module. For small modules it's not too big a deal, but even then it is very difficult for someone new to the language to learn how follow the flow of data.
Dave Thomas has some interesting ideas about this and other problems, but as I don't do Erlang programming professionally at the moment I haven't had time to really dig in deep.
I don't think there really is. Where I was working, we would just say this process is a gen_server (or whatever), as if it was a type of process, but this is more of an emergent property of the environment, than a named property. If enumerating the processes, you can guess a process is a gen_server based on erlang:process_info(initial_call, Pid), but that's not definitive because it could have started as something else, then used gen_server:enter_loop to become a gen_server, or started as a gen_server and then become something else.
Naming the behavior the same as the module, and including client apis and server and the behavior in the same module is legitimately confusing as well; although, all that being in the same place can be nice, too.
However, it is the case that the most commonly used behaviours are gen_server, gen_statem, supervisor, etc, which do live in their own processes, and it is arguably most useful to use behaviours to determine the callbacks that an abstracted, general process-managing module uses to hook into the module you write that describes the implementation of a GenServer.
For an example of a non-process-bound use for a behaviour, one could have "ping" behaviour, which describes running an ICMP ping. You could then describe in abstracted form, the common points between an implementation that uses the linux standard ping, fping, a FFI call to low-level OS hooks and network stacks, a call to the new OTP 22 socket module. Or, in a test environment, write a module where it's backed by a stateful lookup table, where you can assume a ping response, but selectively turn off ping responses to IP addresses to simulate a failed ping response and verify downstream effects.
http://erlang.org/doc/man/ssl_session_cache_api.html
If you implement your own cache module (backed by a file, DB, whatever) and it respects this interface, you can then pass it to the SSL functions and they’ll use it instead of the default cache.
It just happens that gen_server is both the name of a behaviour, and the name of a module, which can be a bit confusing. The gen_server module implements a generic server process, which is customized by passing it a module that implements the gen_server behaviour (as an argument of `start_link`).
Mint (HTTP client library) - https://github.com/elixir-mint/mint
Jason (JSON library) - https://github.com/michalmuskala/jason
Tesla (Another HTTP library) - https://github.com/teamon/tesla
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Yeah, the thing that has driven me to FP, and made Elixir/Erlang such a joy is that data and state are like not coupled (not saying they have to be in OOP, but god damn if I haven't had something that should only do a read do a write and fuck me too many times to count). Given the same input a function will always produce the same output, because values are constant. I've been writing Elixir for like 5-6 years now and four of them professionally, and I hope I never go back to a non FP language (save Rust or mind-boggling pay).
It's kind of mind blowing when you realize, at any point in your program, you can simply serialize out your data, inspect it. Try that with a class, good fucking luck with whatever marshaling system you have...
In Elixir/Erlang, all you (generally speaking) ever have are:
- Strings (binaries, bit-strings, charlists)
- Numbers (integer, float)
- Lists (a list of things)
- Maps (a set of keys and values)
- Structs (a map with a predetermined set of keys)
Recursion and pattern matching make for more readable code IMHO. Here's a fairly trivial snippet from the other day, of converting structs to maps (which Elixir doesn't do implicitly): https://gist.github.com/tehprofessor/fd8aebeb4804201a49f37d9...
The biggest thing to keep in mind coming to a BEAM language from somewhere else is that both the language you're using (Elixir/Erlang/LFE[1]/etc) and the runtime were explicitly designed together to solve a specific category problem (distributed systems). This very unique combination provides, IMHO, the best environment you could ever want to run code in...
In most languages you start up your server in its own process. Want to debug it? You gotta restart the process and then put your debug point in. Not the case in Erlang/Elixir, here's how I start up the Phoenix framework:
iex -S mix phx.server
What that does is both (a) starts the server, (b) opens up an interactive repl for the running application. You can then interact with the running system as it is, and holy shit does it make debugging wonderful.
Want a fast cache for that one operation but don't want to setup X, Y, or Z? Use ETS it's built in: https://elixir-lang.org/getting-started/mix-otp/ets.html
I can't tell you how much frustration I've saved just having reliable mechanisms for timing (thanks pre-emptive scheduling) like `Process.send_after` https://hexdocs.pm/elixir/Process.html#send_after/4
Need to make sure you're only sending messages to live nodes? `pg2` (process groups to the rescue): https://erlang.org/doc/man/pg2.html
Something in Erlang just too slow, write a NIF (but really don't; this (NIF) is a last resort and the only way to you're likely to ever actually crash the VM). You can see a VERY simple example I have in the `wyhash_ex` directory: https://github.com/tehprofessor/shorts (please note shorts is just a toy project, and not quite complete as I got obsessed with the `gen_tcp` part).
Finally, while yes processes, are the fucking peanut butter, jam, and jelly-- you really don't end up using them directly that often in your day to day life. If they aren't making a ton of sense or you don't find yourself using them everywhere, don't sweat it-- when you need to they'll be the obvious solution (even if implementing that solution isn't obvious at first b'cuz learnings).
If you have any Elixir questions, I'm available on Twitter at the same handle as my Github links. Also, the Elixir slack is quite great as well.
[1] LFE is List Flavoured Erlang
Edit: Fixing formatting. God damn I suck at this.
This excerpt caught my attention:
> I've been writing Elixir for like 5-6 years now and four of them professionally, and I hope I never go back to a non FP language (save Rust or mind-boggling pay)
Is there such a big market for Elixir these days? I thought it was very nichey yet.
I think it's been growing pretty steadily, IMHO, because Elixir/Erlang is such a wonderful platform for development, BEAM is extremely battle-tested at this point, and performance is quite good for how easy it all is... also, while I spoke against it, when you absolutely must, to you _can_ write something in C fairly easily (I've _never_ had a good time trying to do C-interop in Ruby or JavaScript for example).
I always wanted to learn it deeply, since I appreciate functional and the concept of Actors, but never thought I would find a job for it easily... I'm changing my mind now.
Thanks for the enlightening!