Adding dependencies during REPL-driven development

Developing in a repl is a different paradigm, and one that you won’t want to leave. It’s like the fun part of web development, after you’ve experienced proper hot-reloading and can’t imagine living without it. Once you’re in that flow, you start to notice the things that throw a wrench in it. Please don’t break my flow!

One flow-breaking culprit you’ll encounter is adding a new package. I recently decided that this problem must be solved already, and sure enough, a search revealed a few solutions. As always with Clojure, the community is great and the tooling is evolving, so every piece of the chain has a history. My goal in writing this is to share what worked for me and prompt anyone doing it better to let me know what that is, because I want it!

A thread in Clojureverse from January of this year covers this area somewhat: What’s the right way to hot-reload dependencies without restarting the repl?

I know rschmukler uses wing.repl/sync-libs for this, but I have not yet integrated that into my workflow, mostly because the below worked for me without adding any new deps.

I could stand to take more advantage of the src/user.clj namespace, as it is central to solving the need here. The user namespace seems to provide a space for dev-only functions, and it is the default namespace entered when starting most repls.

(ns user
  (:require
   [cemerick.pomegranate :refer [add-dependencies]]))

(defn add-dep
  [coords]
  (add-dependencies
    :coordinates coords
    :repositories (merge cemerick.pomegranate.aether/maven-central
                         {"clojars" "https://clojars.org/repo"})))

(comment
  (add-dep '[[teknql/systemic "0.2.0-SNAPSHOT"]])
  (add-dep '[[hawk "0.2.11"]])
  (add-dep '[[cuerdas "0.3.2"]])
  (add-dep '[[com.cognitect/transit-cljs "0.8.239"]
             [com.cognitect/transit-clj "0.8.300"]]))

Evaluating the above (add-dep ...) calls was enough for me to keep going without a restart, and try out a library a bit before adding it to my deps.edn. It does duplicate some of the work though - you’ll still need to add it elsewhere, or you’ll have an issue the next time you start your repl.

This also implies a pomegranate dependency, but for emacs/cider users, these are typically included already by cider’s jack-in command, so there shouldn’t be any extra work beyond the above function.

How do you dynamically add clojure deps? What else interrupts development flow that shouldn’t?

I’d love to build up a documented answer to every repl-flow interruption. Fight for flow!