An Architect's View

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Chlorine: Clojure Integration for Atom

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I’ve been using the Atom editor for about two years now. I switched from Emacs after Clojure/conj 2016, having seen Jason Gilman’s talk about ProtoREPL [video]. It may sound like heresy, but I’d never been happy with Emacs – not 17.x back when I first started using it, not 18.x, not 19.x when I first stopped using it, nor 24.x onward when I came back to it after learning Clojure a few decades later. I built several configurations from scratch, I tried several “curated” configurations, none of them felt like “home”. Emacs just leeched too much of my development time for my tastes. I wanted a simple, modern text editor, that offered a wide variety of “plugins” and supported all the languages I used, with a sane set of defaults. Atom – with ProtoREPL – seemed to be exactly what I was looking for!

And for two years, it has been my day-to-day development environment.

But it has been frustrating that ProtoREPL hasn’t been getting a huge amount of love lately. Two releases immediately after that Conj, eleven in the first half of 2017, and just three since then (in a year and a half). With the advent of Clojure 1.10 and REBL, I wanted to extend ProtoREPL so I could integrate REBL into my workflow, so I forked it and hacked in inspect-block and inspect-top-block functionality (see the commit log). But it’s written in CoffeeScript and that made me sad.

I’ve also had a bit of a long-running love/hate relationship with nREPL over its lifetime. Something about the wire protocol and overall architecture of it just bothered me and I longed for tooling built on what Clojure provides out-of-the-box. When I saw prepl drop in the Clojure 1.10 development cycle, I was very excited: built-in support for future tooling, on top of the Socket REPL we’ve had for a few releases!

I’d previously used Unravel to interact with several of our processes at work that spawn a Socket REPL and found that a very pleasant experience (side-loading Compliment to provide auto-completion while typing).

Unravel is a simple command-line client for Clojure REPLs. It is based on the unrepl protocol, so instead of relying on nREPL, unravel communicates with your Clojure process through a Socket Server REPL.

“instead of relying on nREPL” was music to my ears – I wanted editor integration that worked this way!

A few days ago, in a side-thread in the #off-topic channel on the Clojurians Slack (sign up here), that had started with a question about Cursive vs Emacs/CIDER, Maurício Szabo mentioned “a (very experimental) package for Atom that … uses socket repl”. I was intrigued. Could this be what I’d been looking for?

That package is Chlorine for Atom. I installed it immediately (and disabled ProtoREPL) so I could take it for a spin! It’s written in ClojureScript. It only needs a Socket REPL. It uses unrepl to “upgrade” the REPL as needed. It uses Compliment for auto-completion. I could connect it directly to various running processes and I could start REBL up from the command-line with a Socket REPL and connect to that as well. This was exactly the workflow I’d been looking for!

Maurício has been awesome to work with and over the last few days he’s added the first version of “go to definition” as well as merging pull requests from me to add support for running tests in a namespace or an individual test. I have pull requests in for adding “load file” (it already had evaluate selection, so you could “select all + evaluate selection” but I was used to “load file” from ProtoREPL), and “show source”.

I’ve also ported across my “inspect” functions from ProtoREPL so my entire, day-to-day workflow with ProtoREPL is now possible with Chlorine, REBL, clj, and a couple of aliases – and I have an eminently hackable editor plugin, written in ClojureScript with a slick auto-compile, auto-reload workflow (thank you Maurício!).

I’m still looking forward to tooling based on prepl so the client libraries can be even simpler and smaller but, for now, I’m a very happy developer and I’m very pleased to see how the Clojure community continues to innovate around tooling (which, yes, has needed a lot of love over the years!).

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