core.async VS reagent

Hey, how you doing? This article was written right after I had to painstakingly read the clojure.core.async source code in order to finish a task. So, I hope I save you from the same fate as I had 😄.

It was created by Rich Hickey: https://github.com/clojure/core.async/commit/47b1d24c0291050a1188dbeee2fc9227f694eb3c don't think he's disavowed it lol.

Some time ago we developed some helpers using the capturing notifications strategy to test asynchronous ClojureScript code that was using core.async channels. Have a look at, for instance, the expect-async-message assertion helper in which we use core.async/alts! and core.async/timeout to implement this behaviour. The core.async/alts! function selects the first channel that responds. If that channel is the one the test code was observing we assert that the received message is what we expected. If the channel that responds first is the one generated by core.async/timeout we fail the test. We mentioned these async-test-tools in previous post: Testing Om components with cljs-react-test.

Hi there I'm using Clojure almost a year. I've played with both Manifold and core.async a bit but I'm not %100 sure when to use core.async over Manifold or vice versa.

If you're not familiar with lisps in general, it might be hard to grok the differences between lisp-macros (as used in Clojure) and "normal" macros you see in other languages.

But, if you are familiar already, and just wanna see examples of neat macros that makes the API nicer than what a function could provide, here are a few:

- https://github.com/clojure/core.async/blob/master/examples/w...

- https://github.com/weavejester/compojure

- https://github.com/ptaoussanis/timbre

- https://github.com/krisajenkins/yesql

https://github.com/clojure/core.async

> and with a very poor tooling (lack of IDE's)

Lisps have fantastic support in Emacs and VSCode and are in general simple enough languages that often the heavyweight of an IDE is not needed. But if you want IDEs there are:

If you don't want to block the current thread, you can do the looking/waiting on another thread via thread or in a go using alts! .

Generating `HTML` from lisps has poisoned any other approach for me, see for example https://www.neilvandyke.org/racket/html-writing/, https://reagent-project.github.io/, and https://edicl.github.io/cl-who/

Hiccup syntax for Clojure uses hash maps (curly braces) for attrs, e.g. `{:style {:background "red" :margin "1em"}`

See Reagent which uses Hiccup synta: https://reagent-project.github.io/

    (defn simple-component []

* Single-Page App: shadow-cljs for the build concerns (https://github.com/thheller/shadow-cljs), Reagent with Re-frame for complex/large app (https://reagent-project.github.io and https://github.com/day8/re-frame). Even if we now prefer using HTMX (https://htmx.org) and server-side rendering (Hiccup way of manipulating HTML is just amazing, https://github.com/weavejester/hiccup).

The API documentation lists the most commonly and rarely used parts before going into detail and there are many usage examples.

Reagent has a nice intro tutorial (classic todo-app): http://reagent-project.github.io and many other helpful tutorials and resources for beginners: https://cljdoc.org/d/reagent/reagent/1.2.0/doc/documentation...

However, since Reagent is still stuck with class-components for more complex behavior and relies on Hiccup, which is nice but has a performance cost compared to pure React, I am unsure about its future. Like some others in the Clojure community, I have moved to thin React wrappers like Helix and use Refx to integrate those with re-frame. It may be a bit confusing right now for beginners since there is no “golden path”.

Also, unfortunately, many smaller libraries are poorly documented and it seems like it is expected from the developer to dig into the source code to find out what’s going on.

What I found the most difficult as a beginner was how to setup a project in ClojureScript in the first place, like all the configuration in shadow-cljs, how it interacts with deps.edn, how it integrates with npm, the REPL, etc. But dev/build config has always been a weak spot for me, so it might be just that.

Overall, I still very much enjoy working with Clojure(Script), more than in any other language. Anyone who likes Lisps and functional programming should give it a try (and be sure to watch Rich Hickeys amazing talks!).

have you tried cljs and reagent? it’s a different vibe.

my bootstrap: https://github.com/nathants/aws-gocljs

the project: https://reagent-project.github.io/

Clojure people have been doing this for a decade or so. It’s really so much better to work with. All started with Hiccup and when React came along you got Reagent and many more developments building on the idea.

> But Reagent supports functional components as well, with hooks and all.

I addressed this already: while reagent is able to emit function components, there is a performance penalty to this.[1]

> I also very much like Hiccup, and so do many of us, because code is data and data is code, and Helix has decided not to support that.

Hiccup is convenient to write, but it is a constant run-time cost and a significant storage cost given that you have to store long series of constructors to cljs.core.PersistentVector in your bundle, have the JS runtime actually construct the vector, then pass it through a Hiccup interpreter to finally produce DOM nodes and throw away the persistent vector, only to repeat this entire process again on re-render.[2]

> Helix has decided not to support that.

That is simply not true. From the Helix documentation[2],

> If you want to use libraries like sablono, hicada or even hx hiccup parser, you can easily add that by creating a custom macro.

These are all Hiccup interpreters you can readily use.

IME there is very little difference between using the $ macro in Helix and writing Hiccup. I do not really miss Hiccup when I use Helix, and you still have data as code ;)

While this is from an unrelated project, there are benchmarks[3] done against Reagent that demonstrate the sheer overhead it has. In practice it is not a big problem if you rarely trigger a re-render, but otherwise it is a non-trivial cost, and if you want to use modern React features (like Suspense), there is a lot of r/as-element mingling going on, converting cases, etc. that simply make Reagent feel more tedious to use than Helix.

Also, the newer UIx2, which largely borrows from Helix, is "3.2x faster than Reagent" according to one of the contributors.[4]

I think it'd be worthwhile to benchmark all of these libraries against each other and record the data in one place. Maybe I'll get around to doing it this weekend :)

---

[1] https://github.com/reagent-project/reagent/blob/master/doc/R...

[2] https://github.com/lilactown/helix/blob/master/docs/faq.md#w...

[3] https://github.com/roman01la/uix#benchmarks

[4] https://github.com/pitch-io/uix/pull/12

Reagent is peak React. All the good stuff without any of the hook and readability problems the article describes.

No affiliation, happy user for years.

https://github.com/reagent-project/reagent