Elixir protocols vs. Clojure multimethods | Hacker News Reader

Elixir protocols vs. Clojure multimethods

mattmower.com

160 pointssandbags89 comments

> Now Elixir has an equivalent to multi, the Protocol.

For what it's worth, Clojure also has a much closer fit to Elixir Protocols called... a Protocol.

https://www.braveclojure.com/multimethods-records-protocols/...

They too can only dispatch on the type of the first argument, but are more structured (you can add multiple pieces of behavior at a time) and performant than multimethods where that's the behavior you're looking for.

I'll also leave these here, in case the conversation inevitably turns to pattern-matched function definition in Elixir. :)

https://github.com/clojure/core.match -- pattern matching as a library

https://github.com/killme2008/defun -- using core.match to implement Elixir/Erlang-like function definition

https://github.com/noprompt/meander -- advanced pattern matching, for some fun and flavor :)

What's also fun is that core.match is implemented using a paper from INRIA on how to efficiently convert patterns into decision trees:

https://github.com/clojure/core.match/wiki/Understanding-the...

I've always loved that paper. Very readable, and gives good insights.

If videos are more your speed, David Nolen, the primary author of that library (and article) has a talk about it as well: https://www.youtube.com/watch?v=TVJa-V6U-XI

Elixir's Protocols actually were inspired by Clojure Protocols.

Here's Jose Valim talking about it:

> I’ve learned a lot also from Clojure because, at the time I was thinking about Elixir, Clojure was already around. I like to say it’s one of the top three influences in Elixir

[...]

> The main, the top three influences are Erlang, Ruby, and Clojure.

[...]

> I was like, no, but I’m going to call them protocols because there are a lot of similarities between Clojure and Elixir in terms of them being dynamic languages and in terms of the macro system. I was like, okay, I’m going to call them protocols because the closest thing we have today to what I want is Clojure

And he goes on talking about more inspiration and similarities from Clojure like Agents, etc.

Full exert is here: http://blog.cognitect.com/cognicast/120

Having worked with both to create the same system (building a game server) I've found Clojure actually sits better with the functional thinking style (1 data structure, 100 functions).

While Phoenix was the killer app for Elixir, and Elixir has far superior readability (using the Ruby syntax); there were couple of things that were off-putting and I struggled with them.

1. everything is inside a module was an unnecessary distraction

2. And then the separation between anonymous and named functions simply were unnecessary

3. And that I would have to declare the data / record inside a module (??)

Elixir felt like a functional language un-necessarily trying to look like a class based language.

I sometimes feel that had Elixir had only supported functions outside of modules... oh that freedom.

But some of the thought that went into Flow, Channels (which has become the de riguere now), mix (developer ergonomics ftw), those micro-second latency responses, distillery are still too classy and amazing.

> Elixir felt like a functional language un-necessarily trying to look like a class based language.

Not really. Named functions live in modules because that is how it is done in Erlang; Elixir is compiled to Erlang's abstract syntax. In practice does anyone define Clojure functions outside of a namespace? Haskell functions are always defined in modules too, do you think they got that from class based languages?

The problem here is that its inconvinient to define a function at the Elixir REPL because it demands that it be put inside a module.

Clojure REPLS allow switching the namespace, and anything you define goes intoo the current namespace. So it is more ergonomic.

IEx will let you define a module at the REPL. Combine that with a macro (exercise for reader) in your .iex.exs which expands a function into a module definition and imports it and you're in business.

    iex(1)> defmodule Foo, do: def bar(x), do: x + 1
    {:module, Foo,
     <<70, 79, 82, 49, 0, 0, 4, 192, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 135,
       0, 0, 0, 15, 10, 69, 108, 105, 120, 105, 114, 46, 70, 111, 111, 8, 95, 95,
       105, 110, 102, 111, 95, 95, 10, 97, 116, ...>>, {:bar, 1}}
    iex(2)> Foo.bar(1)
    2
    
    iex(3)> import Foo
    Foo
    iex(4)> bar(1)
    2

Yup, like I said, not as ergonomic as Clojure.

In clojure, it is:

    user> (defn bar [x] (+ x 1))

If you want it inside a namespace named foo, then it is:

    user> (in-ns 'foo)
    foo> (defn bar [x] (+ x 1))

I agree Clojure has a better REPL experience than Elixir. But in Elixir REPL for a quick and dirty function you'd probably just do

    >bar = fn x -> x + 1 end

The most unfortunate thing though is then you have to have a different calling convention. Its the greatest flaw in Elixir by far but they didn't have a reasonable alternative given the constraints of Erlang.

Still for defining a named function in the REPL its the same in Haskell and most other languages I believe that you can't define a new named function or add a function to a module in the REPL, though at least in Haskell the calling convention for a variable bound to a lambda is the same as for a named top-level function. LISPs have always had a different notion of how the REPL integrates into the development experience of a running program, and I don't think its really been replicated elsewhere.

Or maybe go with the shorter anonymous function syntax:

bar = &(&1 + 1)

If we're playing code golf, then in Clojure it is:

    (def bar #(+ % 1))

or even

    (def bar inc)

but the difference is that in Clojure, all of these are `IFn`s, and have the same calling syntax, unlike Elixir.

You may be "playing code golf", but I generally just use the capture syntax where the compactness aids readability. For example, a function that takes two arguments and returns their product could be written as

fn x, y -> x * y end

&(&1 * &2)

When used inside a map or reduce or when the function is a direct mathematical operation on its arguments, it can be a bit quicker to parse the capture syntax than the fn ... end syntax.

True. The heritage of erlang is undeniable here.

In Clojure too, the fns, records everything live inside a namespace but that is a modularity mechanism for code organisation.

I had most of these concerns when I was early learning the language. I found it annoying to have everything in modules. Now, however, I've come to appreciate the organization and structure that this forces upon the programmer.

It makes me structure my code and group related concerns at time of writing. I now code my functions as a working collective rather than individual items.

And with .exs files, you can have multiple modules in one file for quick scripting.[0]

[0]https://github.com/matteing/stack/blob/main/server/boilerpla...

This was one of my big impressions of Elixir. It forces you into so many things that improve long term maintainability.

Which is exactly what class based modularity provides

I have had the same experience!

The distinction b/w anonymous and named functions is especially icky.

I also agree that Elixir leads to more readable code, lots of people in the Clojure community tend to write dense one liners to appear "cool".

I have a feeling it’s not to appear “cool,” but because when you’re writing code there is a tendency to prefer higher density.

Why?

Because higher density makes it easier to see the entirety of a context: more code on the screen makes it easier to spot the relationships.

This happens in other languages too, of course, but it’s easy to see why Closure pushes flow in that direction.

I've seen inscrutable one-liners with Elixir's capture syntax, too (and written some myself :) )

Sounds like you would love Nim.

You can just ignore modules/namespaces. While you have some procedures private to the file, you can expose them and they're just in the global namespace.

Maybe my enjoyment with Nim is partly due to the (awesome!) boringness of Elixir at times. I write Elixir code. It mostly just works with a few simple abstractions. Nim's more fun for MCU's and fast code where allocations count and I don't care about scalability of the application as much. I rather enjoy both.

Like others all of my Clojure code was in namespaces so I see it as a wash between the two. In practice I cannot imagine any real app not making use of such modularity.

I too found the "." syntax for anonymous functions a bit jarring at first. Why treat them differently? In practice I don't even notice it now. It's never been confusing, it's just a wart.

Also, I found the one-struct-per-module thing a bit odd to begin with but in practice it makes a lot of sense. Also since you can put modules inside modules it's no encumberance if you want to declare a number of related structs. Again, once I was used to it I apprecitated the simplicity.

I disagree with your characterisation: I perceive no "class-based"'ness about Elixir. Do you have some examples? Perhaps there is somethign I have missed. So far, given that it's not exposing a class based system underneath, Elixir has seemed even further from this than Clojure.

And I have, in general, found the tooling support friendlier for Elixir. The only thing that I really gripe about is the inability to communicate between editor and REPL.

My “impression” of class based comes from the usage that defrecord was to be inside a defmodule only; not as free floating records.

About the tooling definitely yes. Elixir is pretty pretty good; at compile, build and employ time.

I recently found there was a clojure implementation for .NET and also one for the BEAM Virtual Machine. Has anyone used the latter? Regards

[1] https://github.com/clojure/clojure-clr [2] https://github.com/clojerl/clojerl

There is also lfe [1] which is a lisp for the BEAM VM

[1] https://lfe.io/

And also https://github.com/clojerl/clojerl

There is also ClojureDart in the making. That one seems quite promising.

Why do you say "was"? They are both still actively developed even if not very popular.

You can, you can match against the module in the struct of the second parameter, concatenate the two modules, and manually dispatch against the concatenated module. I don't really recommend this (it is not performant and feels like a code smell), but it is possible

    defmodule A do
      defstruct [...]
    end
    defmodule B do
      defstruct [...]
    end
    defprotocol C do
      def foo(a, b)
    end
    defimpl C, for: Any do
      def foo(x1 = %m1{}, x2 = %m2{})
        Module.concat(m1, m2).foo(x1, x2)
      end
    end
    defmodule A.A do
      def foo...
    end
    defmodule A.B do
      def foo...

Ah, this is very neat.

yep. pattern matching on the `__struct__` sugar, the poor man's protocol!

Does performance matter considering Elixir is already very slow in per-thread performance?

depends on what you are doing. And it's not necessarily "very slow", moving forward as the JIT gets better and better. I highly doubt that this technique is going to be very jittable.

How is it slow?

How? Do you mean how do I know it's slow? Because it takes longer to run.

Write a typical computation such as Fibonacci in Java and Erlang/Elixir and compare. Fortunately someone has already done this.

Elixir is 3x slower than C and 2x slower than Java for this single thread example.

https://github.com/drujensen/fib

Apparently this upsets people for me to point this out. However, I did not say that Elixir was slow in general or a bad choice. It's an excellent choice for problems which suit parallelization or which require reliable, consistent performance.

Since the parent poster had commented that adding this multi-module dispatch would not be performant, I merely pointed out that the single thread peformance was already slow (as in, why worry too much about the performance cost of the multi dispatch suggestion).

I’m starting to get a bit fed up with the down-voting behaviour here recently.

It used to be that on HN you down-voted for people who were obstructing conversation, being disingenuous or in some cases being excessively disrespectful.

Now having read 3 of your comments and seeing all 3 are heavily down-voted and yet the content of your messages is constructive and interesting.

If you disagree with something, fine, just don’t vote on it. Save the down-votes for bad actors, not someone with a different view.

The last thing HN needs is to become the kind of place where you’re actively encouraged to karma farm or whatever that term is for that behaviour on reddit.

I think they were downvoted because the first response was almost contentless and the other posts complain too much about the downvotes. Yes, there is some "good info" there but basically they are still presented in a relatively context-poor fashion and defensive, and willfully ignoring other points being made, and most active practitioners of elixir are aware of the context, so the comments are of questionable utility except for people who don't use the system, who may interpret it out of context and come to conclusions that are wrong. In short, they still have a shitposty feel.

Eh, I'd rather the thread discussed the language features in TFA. Once again, a potentially interesting comment section is sidetracked by yet another referendum on {{ niche_programming_language }}'s application to web development. Can't we just keep this to release posts?

HN now has lots of folks that just down vote when they disagree, as it happens in many other communities after they grew beyond a specific user base.

I always made my statements the way I feel like, since the BBS days, and voting systems haven't change that.

There will always people that want to silence you, regardless of the medium.

Life is too short to care for them.

It’s slower for an operation like that because of the scheduler ensuring a single process isn’t hogging all of the CPU.

When was the last time you needed to write a Fibonacci for anything you’ve built in your career?

It’s a benchmark that doesn’t show anything useful for real world applicability.

On the web site of things, it is faster than Rails, Django, Laravel, Express and even Spring, and this is with Plug and Ecto. https://www.techempower.com/benchmarks/. That seems to be very good performance to me.

People go nuts here on HN if they think you said something bad about their baby.

I said per-thread, but I meant single-thread... as in CPU bound single process activity. That is undisputedly slow compared to languages like Java, C/C++, Go, etc. That is also very much not what Erlang is designed for. It adds a lot of overhead with the supervisor and other features which do not give a benefit for single thread CPU heavy activities.

And since the parent poster mentioned the multi-dispatch approach would not be performant, I attempted to suggest that the performance cost of that would be less relevant considering Elixir is already not very performant in single thread cases. In other words, it was a moot point.

I never said that Elixir/Erlang was slow for multi-thread/process distributed activities. Obviously that is where it really excels. But if you want to crunch numbers sequentially in a way that cannot be spread across multiple processes/threads, then you will find Elixir to be slow.

The benchmarks you are referring to are very much multi-thread comparisons. They are specifically NOT what I was was slow.

You're right about the performance of single-threaded vs multi-threaded Elixir. However, I used web apps as a comparison because they are the most common use case for Elixir. Considering here Elixir performs very well, performance could be one of the reasons why people choose it. In that case, being aware of performance pitfalls is a good thing.

I don't agree that performance is a moot point if what you use is slower than some alternatives, and I think that's the main point where we disagree.

I am not a fan of slowing something down, but in the multi-method dispatch example, unless it was being exercised in a tight loop (which would seem very much like a single thread CPU bound scenario which is already a problem), then it wouldn't be exercised often enough to make a big impact. That's just my gut feeling based on my experiences.

But if this really is a big deal, then it would be fair to consider the other language features which do not contribute to the reliability, scalability, and other core Erlang/BEAM features. For example, what is the cost of pattern matching in general? Doesn't that add considerable overhead, just for the benefit of making code cleaner? If that's acceptable, then I don't see why "just one more" feature - in this case a homegrown multi-method dispatch across modules - should be considered non-performant.

Pattern matches should execute in linear time in the worst case worst. Generally you want to place the most likely and specific matches first.

Good point about the tight loop. For the other part, my gut feeling would be that there is a "base language" that most developers are familiar with, and accept the performance/other things tradeoffs of, but for more obscure features, people are explicit about these points because they are less known.

https://github.com/OvermindDL1/protocol_ex gives you protocols with full pattern matching.

Brilliant, thank you.

I assumed that, with Elixir macro support, someone could implement protocols with full pattern matching. Just way above my current pay grade!

Using dashes in function names? Blasphemy

That’s called “kebab case”. When your language supports it, you know the language is good :)

Funky, I hadn't even noticed I had switched back when I started thinking about Clojure and that it's not legal Elixir. I had to go check my Elixir code to find the _'s!

Feels like Elixir has stolen much of Clojure's appeal and 'thunder' as the niche pragmatic functional language.

The ruby-like syntax and the VERY open and newbie-friendly community have definitely contributed to this.

I've been to Elixir conferences, and they felt like people were just encouraging each other to build solid software WITH each other. I've not seen this level of camaraderie for other programming language communities.

Elixir devs — and I am super biased here — are a special bunch :)

Community can definitely play a role though I can't help but think that Phoenix and the proselytizing done by Jose and co are the main factors.

Sure, we have Luminus in the Clojureverse but its just not as easy and straightforward as the Rails-like experience of Phoenix. You don't have Hickey personally responding to comments on HN/Reddit etc.

Hickey is extremely remote from the Clojure community. Most of Cognitect is. Really, only Alex Miller engages on a regular basis. To a lesser extent, Fogus and Ghadi do, too.

The Clojurescript community is friendlier, IMO.

Much to the detriment of the language imo, and he didn't help the feeling when he released 'Open Source is not about you'

I would agree here that the combination of being "closed to collaboration", the slow pace of development lately, and really infrequent communication from the sole owner/leader/BDFL does send a weird vibe and raises some concern regarding what direction the language is going to be going in in the future.

Isn’t one of the beauties of lisp is that you don’t need much from the language creator. It should be far more stable than non-lisp languages, and you can implement most ideas with macros outside of the core language.

You can get a pretty long way but there are still things that need to be improved over time. For example Clojure still 7 years after the java 8 release doesn't have great integration with java 8 functional interfaces, which is a pretty big detriment to java interop. I saw this patch which seems to have been submitted by a community member https://clojure.atlassian.net/browse/CLJ-2637 (not sure if the author is a core contributor or what), but even after month no comment from Rich or anyone else on the team to indicate if this is a good idea, if they'd let it in or what.

One of the big reasons, in my opinion, for Clojure failing to fulfill its potential as a mainstream language. Clojure had SO much going for it then it just flatlined. Sad indeed and very much down to its stewardship.

Maybe not, but I do agree with him, too many people in open source feel entitled to get stuff for free (beer) without contributing, many corporations that leech on open source as well.

For the most part, Clojure is tuned for experienced developers I think. It's kind of an oximoron, but it feels like it was Rich Hickey's goal as well, to not appeal to any of the "easy" and "convenient" and "familiar", but focus entirely in "no bs", "simple" and "very flexible" pieces that never break backwards compatibility, are always open for extension, keep performance in mind, reaches for battle tested hosts when it can, and all that.

That's great to hear! I get the same feeling towards the Clojure community as well, some of the friendliest, smartest and most helpful people hanging out at the Clojure watering holes (in comparison to other languages I've worked with). I also am constantly in awe of the output of the Clojure world. There are like 3 or 4 great podcasts going, so many cool projects being worked on, especially for a community which seems to be sadly so small.

Which podcasts do you recommend?

I like:

Defn: https://podtail.com/en/podcast/defn/

The REPL: https://www.therepl.net/episodes/ (Seems to have gone quiet)

ClojureScript Podcast: https://clojurescriptpodcast.com/

Functional Design in Clojure: https://clojuredesign.club/ (Also seems to have gone quiet since December)

LispCast by Eric Normand: https://lispcast.com/

Cognitect, the company behind Clojure also has their own podcast but I haven't found it to be that interesting most of the time, at least yet: https://www.cognitect.com/cognicast/index.html

Not specifically Clojure-related but has discussed a few times including wit Rich Hickey (as well as other unrelated great conversations!): CaSe https://www.case-podcast.org/

Completely not at all about Clojure but great software podcasts:

Go Time: Even though I hardly ever write Go, I find their conversations to be really great and having lessons beyond Go. It helps that I am interested in the language though: https://changelog.com/gotime

Web Development and Development in general - The Bike Shed: https://www.bikeshed.fm/

Software Engineering Radio: https://www.se-radio.net/

CoRecursive: https://corecursive.com/

Inside Java: https://inside.java/

Thanks!

I’ve listened to some Defn with mixed results. I really liked their interview with Daniel Higginbotham, especially when they argued a bit about what “simple” means.

Even if some of the others have gone quiet, there plenty of backlog to choose interesting episodes from. The Bike Shed also looks right up my alley. They probably should have had some more discussion before choosing that name, though.

There's a big downside to Clojure having the most amount of experienced developers I think in bringing beginners in. You'd think it be the opposite, but beginners are better treated by other passionate smart beginners and people who just got out of being a beginner. As experienced old devs tend to not have the time or patience or not know how to explain things or make it beginner friendly.

Come on, every language community says that about itself. Rust is the latest "amazing" community.

Elixir seems to be very approachable. But some of the strengths of Clojure are unmatched, such as Java/JS interop, isomorphic code for web development, and generally being a Lisp (which includes macros).

LiveView sorta tackles the isomorphic web development side, and while I agree that Lisp is a better syntax you do have hygienic macros in Elixir as well.

Elixir has macros too.

Elixir has Erlang interop. Erlang is a 30 year old language.

Yes and no. Yeah Erlang has been around for 30 years but "30 year old language" makes it sound like it came out 30 years ago and then stopped. Erlang is still being very actively developed and improved, it's by no means a crusty old language.

I'm not sure what the implications are of either comment. Both Java and Javascript are reaching the 30 year old mark as well.

Elixir has macros. People are currently building Nx https://github.com/elixir-nx/nx while not having to change anything in the language. Java/JS interop being unmatched is true, but Elixir has Erlang interop too.

Elixir afaik has taken a lot of inspiration from clojure and lisp type languages.

It's not readily apparent from the ruby like syntax though.

its funny you say that, Ruby ALSO took a lot from Lisp and lisp like langugaes. there's even a built in parser in Ruby that converts the language into S-expressions

  require 'ripper'
  Ripper.sexp('a && b')
  => [:program, [[:binary, [:vcall, [:@ident, "a", [1, 0]]],    :"&&", [:vcall, [:@ident, "b", [1, 5]]]]]]
  Ripper.sexp(<<-RB)
    if a
      b
    else
      c
    end
  RB
  => [:program, [[:if, [:vcall, [:@ident, "a", [1, 5]]],   [[:vcall, [:@ident, "b", [2, 4]]]], [:else, [[:vcall, [:@ident,  "c", [4, 4]]]]]]]]

Ruby is just way denser than most lisps.

I love Ruby, Elixir, and Lisp(s)

Didn't know that!

One striking similarly Elixir has to lisp style languages is the macro system. You have quoted and unquoted expressions just like lisp.

And like lisp most of Elixir, down to the low level stuff like if statements, modules, and so on, is built up from a few primitives.

Here are the primitives that the Elixir language is built from:

https://hexdocs.pm/elixir/1.12/Kernel.SpecialForms.html

To me, F# is the pragmatic functional language with the most appeal, but being on .NET maybe it’s not even niche.

It kind of is, to .NET developers.

Although Microsoft has made it from Microsoft Research into official Visual Studio, it has been mostly an up hill fight to keep it there, while .NET languages group mostly cares about C# and VB, and to certain extent C++/CLI for integration with Windows APIs.

F# when taken into account by management, comes always after those three.

Most of the Visual Studio tooling for C# and VB isn't available to F# projects, you are supposed to do it manually, e.g. GUI designers, EF database to code generation, .NET 5 code generators.

Honestly I wouldn't be using Elixir if it wasn't for my co-founder's singing the praises of Phoenix & Liveview. I'd tried it once about a year ago but couldn't see any advantage over Clojure (esp. with re-frame). Sadly he was never going to move to Clojure.

That said, now I've dug in and really used it for solving some problems I am finding it an elegant and enjoyable experience.

I'd happily use either although I think Elixir has a particular fit to web applications.

Not really. In most job stats I've seen Clojure is ahead of Elixir.

protocols are still just single dispatch like interfaces and virtuals in other languages. This person uses a title that makes it seem like Elixir has multiple dispatch, only to conclude at the end that protocols are nothing like multimethods.

It's one of those "rarely used in practice but insanely frustrating when you write a library or some generalized code".

However, I'd rather Clojure got proper pattern-matching than Elixir multimethods. I find pattern matching a much more powerful, flexible and useful tool.

Why not just use core.match? https://github.com/clojure/core.match

Nice. Didn't know/remember it existed

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