Learning Clojure: first steps
Why Clojure?
It’s been longer than I’d like since I learnt a new programming language. I mostly write Python at work and I wanted to learn something substantially different. I narrowed it down to Elixir or Clojure. I chose Clojure for a few reasons:
- I’ve never learnt a Lisp before.
- Clojure runs on the JVM, so you get Java interoperability. At work I’ve been thinking about Kafka, which has much better support for Java compared to Python, so this is appealing.
- The author of Clojure, Rich Hickey, is hugely influential and I enjoy his talks. Simple Made Easy is a favourite of mine.
- Elixir seems more focussed on highly concurrent applications, which I generally don’t write, so I thought Clojure will be more useful to me.
- My manager sung Clojure’s praises.
Inspired by Julia Evans I decided to write down and share what I have learned and struggled with so far.
I like learning by reading. I dipped in and out of the Clojure getting started guide, Clojure for the Brave and True and Programming Clojure. I wasn’t keen on the style of “Brave Clojure”, but I did enjoy the intro to projects and namespaces. It introduces the project automation tool Leinigen, which seems a bit like Pipenv or Poetry in Python. When I get started with a new language I like to figure out early on the idiomatic way to organise projects, so with lein new app my-project I was sorted.
As a card-carrying member of the test-driven development (TDD) club I started trying to figure out how to write tests. I took a look at the tests in xtdb and clojure.test docs. I can’t remember how, but I discovered that most Clojure developers don’t do TDD like you would with pytest or go test, but they use “REPL-driven development”. I enjoyed Sean Corfield’s talk on the topic.
Sean used VSCode. I like PyCharm with IdeaVim, so I downloaded IntelliJ and the Cursive plugin for Clojure. Starting a REPL is somewhat buried but once you have it running you can evaluate the form under your cursor with cmd+shift+p.
I thought I had gone mad when my IntelliJ wouldn’t let me delete parentheses. It turned out something called paredit was enabled, which enables structural editing. Structural editing takes advantage of Clojure code itself being data (an idea I’m not convinced I understand on a deep level) and all the nested forms ((...), {...}, [...]) forming a tree. But being a beginner I turned it off so I could delete my unwanted bracket and be on my way. It might have been to do with Cursive and IdeaVim not working well together.
Turning off structural editing turned out to be a poor decision and something I’d switch back on, but that’s another post.