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🥷 Clojure Pro Tip 5: Hiccup Raw

whatacold@gmail.com (Ken Huang) — Thu, 15 May 2025 12:49:27 +0800

In case you don’t know it, we can use raw strings, like embedding JS code, in hiccup.

I just found out we can use raw to prevent strings from getting escaped. I used to have to define a dedicated app.js for that, which would need an extra HTTP request.

Hiccup raw in action

Looking back, I should’ve found this at the very beginning, as it’s just mentioned on its GitHub homepage, but somehow I missed it.

🥷 Clojure Pro Tip 4: Cider ClojureDocs

whatacold@gmail.com (Ken Huang) — Tue, 29 Apr 2025 12:49:27 +0800

Sometimes, we may want a few examples of a Clojure API for inspiration while developing, especially when reading other people's or open source code.

With Cider in Emacs, we can run M-x cider-doc to see the docstring for the symbol. We can even use M-x cider-clojuredocs for some examples if the symbol is from the language core.

Running M-x cider-clojuredocs

I happened to find this command recently. I bet I was not the only one who didn't know it, thus I'm sharing.

🥷 Clojure Pro Tip 3: the Thread-As Macro

whatacold@gmail.com (Ken Huang) — Wed, 23 Apr 2025 12:49:27 +0800

So you're more than excited to find out how Clojure's thread macros can make code clean and concise, you just love it! But at some point you'll be trapped a bit as the threaded argument's positions are inconsistent using -> or ->>.

Luckily, you can use as-> to place the argument wherever you like:

Lambda vs. thread-as

🥷 Clojure Pro Tip 2: group-by

whatacold@gmail.com (Ken Huang) — Fri, 18 Apr 2025 12:49:27 +0800

It's amazingly easy to group things in Clojure. The language core provides a group-by function directly. Together with many built-in functions or key functions, it creates a ton of possibilities, and we can also bake our grouping function if none is satisfying.

group-by

Example from Clojure Koans.

Collecting Events to Google Analytics using ClojureScript

whatacold@gmail.com (Ken Huang) — Fri, 11 Apr 2025 22:49:27 +0800

When you’re building a side project, chances are you need to collect user events so that you can understand user behaviors better and eventually improve your product.

So recently I made a small ClojureScript library for that, it supports web apps or chrome extensions. Check it out at https://github.com/whatacold/google-analytics, it also contains a demo project using shadow-cljs as the build tool.

Hope it helps, and give it a star ⭐ on GitHub and share it if it does, thanks!

🥷 Clojure Pro Tip 1: the Discard Reader Symbol

whatacold@gmail.com (Ken Huang) — Sat, 05 Apr 2025 12:49:27 +0800

In Clojure, we can use comment (aka Rich Comment Blocks) for tests or experiments in development. However, since a comment evaluates to nil, you may run into surprising results or even errors if you misuse it.

Comment vs. Discard

In these scenarios, you may tend to use ; to comment them out, but a better choice is to use the discard reader symbol #_.

Constructing Clojure Maps Conditionally

whatacold@gmail.com (Ken Huang) — Sun, 05 Jan 2025 10:40:07 +0800

I was wondering how to construct a multi-key map conditionally while I was coding in Clojure. Ideally, I would like to build it "in one pass" like {:bar 2 (when true :baz 3)}, but from what I had collected from Blue Sky, it seemed that's impossible, or it's just not an idiomatic way to program like that in Clojure. (Or, is this just a side effect of writing too much imperative code?)

A Few Quick Notes About babashka/fs

whatacold@gmail.com (Ken Huang) — Sat, 07 Dec 2024 22:24:41 +0800

Recently I've used babashka/fs a little bit, here are some quick notes for it:

Path vs File. Use Path whenever possible, according to this SO answer to "Java: Path vs File". This is actually Java related.
It's ok to use a path as a key for a clojure map. At my first try, I somehow came to the conclusion that it's not ok, while I was refactoring the live reload for clay. And later I found that it's totally fine to use it as a key. 😞
Use fs/path to construct file/directory paths, for example, (fs/path "/tmp" "foo" "bar" "baz.clj") will result in a path object for /tmp/foo/bar/baz.clj on linux. If you're coming from Python, it might remind you of os.path.join(path, *paths).
Use fs/createdirs for mkdir -p, though its name is a bit misleading, I first thought it's for creating a few dirs.
fs/with-temp-dir is convenient for creating tests.

Doing Unit test in Clojure Is Easy

whatacold@gmail.com (Ken Huang) — Thu, 28 Nov 2024 23:10:56 +0800

While refactoring the live reload feature of Clay, I realized I'd better break long functions into smaller and functional ones (as many as I can), which is also a common practice in the clojure community.

Small pure functions not only are easy to verify on the development process (using a REPL), but also are easy to test. And unit tests are easy to write in clojure, just use deftest from clojure.test, a very basic one looks like this:

Adding Clojure Dependencies from the Command Line

whatacold@gmail.com (Ken Huang) — Sat, 09 Nov 2024 21:02:56 +0800

While debugging a live reload issue of Clay a few days ago, I learned from Markus Agwin that we can actually add dependencies on the fly from the command line, just like this: clj -Sdeps "{:deps {org.scicloj/clay {:mvn/version \"2-beta21\"}}}".

Even better, we can add dependency from a Git repo and specify the commit hash: clj -Sdeps "{:deps {io.github.scicloj/clay {:git/url \"https://github.com/scicloj/clay.git\" :git/sha \"35a46541db66ae6b4e1af628b7c24c42d3be418f\"}}}", which is really helpful for experimenting and verifying things.

Some clj links (clj --help has a pointer for these URLs):

Bitten by Lazy Sequence of map

whatacold@gmail.com (Ken Huang) — Sat, 09 Nov 2024 21:02:56 +0800

While impletenting the live reload feature for Clay a few weeks ago, unfortunately, I was bitten by the laziness of map. It seems quite obvious we all know that its result is a lazy sequence, but I just can't help fall into the "trap".

At that time I was adding a vector to keep track of all beholder instances watching file changes in user specified directories. So then when it's time to stop all the watchers, I used something like to achieve the goal:

Anonymous Functions in Thread Macros

whatacold@gmail.com (Ken Huang) — Fri, 08 Nov 2024 21:02:56 +0800

While adding the live reload feature to Clay, I encountered a problem of applying anonymous functions to thread macros. For example, below is a simple snippet trying to wrap the input directory as a vector with the help of thread macro, but surprisingly, it errors out. After some searching, I figured out that I need to put the anonymous function into another pair of parentheses:

(-> "/tmp/"
    #(if (vector? %) % [%]))
;; => Syntax error (ClassCastException) compiling fn* at (simple4all.clj:19:1).
;;    class java.lang.String cannot be cast to class clojure.lang.ISeq (java.lang.String is in module java.base of loader 'bootstrap'; clojure.lang.ISeq is in unnamed module of loader 'app')

(-> "/tmp/"
    (#(if (vector? %) % [%])))
;; => ["/tmp/"]

Paul has a nice explanation on Stack Overflow, thread macros need the function forms to be lists, but anonymous functions are already lists, so the first expression, "/tmp/" in this example, will just be inserted into that list, just as illustrated below:

Starting a Clojure nREPL Manually for Cider

whatacold@gmail.com (Ken Huang) — Fri, 08 Nov 2024 00:02:56 +0800

While troubleshooting and fixing a live reload bug in Clay today, which required to start a minimal Clojure environment, I figured out how to start a nREPL from the command line.

Instead of using M-x cider-jack-in-clj directly from Emacs, actually we can manully bring up an nREPL with this: clj -Sdeps "{:deps {org.scicloj/clay {:mvn/version \"2-beta21\"} cider/cider-nrepl {:mvn/version \"0.50.2\"}}}" -m nrepl.cmdline --middleware "[cider.nrepl/cider-middleware]" (The clay part is only necessary for this debugging), and then connect to this nREPL using the Emacs command M-x cider-connect-clj.