Playing Advent of Code with Squint

In the previous post I described how I built a Cloudflare worker with squint. This worker is part of my attempt to build a playground for squint in which you can play Advent of Code. Advent of Code is a series of programming puzzles published each day through December 1-25. By exercising puzzles solutions on squint, I'm able to detect missing or incompatible features compared to ClojureScript.


The Advent of Code playground can be loaded here.

This link redirects you to the most recent version and I'll be updating the redirected-to link if necessary.

Puzzle input

To play Advent of Code, you need to download your puzzle input:

(def input (str/trim (js-await (fetch-input 2017 1))))

The fetch-input function is pre-defined in this boilerplate gist and is loaded via the boilerplate query parameter. Advent of Code input is personalized and based on your Advent of Code account. This is why you are asked to fill in your Advent of Code token in the top of the UI. You can obtain this token by visiting Advent of Code, registering + logging in and then find the session cookie in the developer console. Copy paste this value into the UI and hit Save!. After doing so, the session token is saved in local storage for next puzzles you might want to solve. The session token is only saved in your browser. The Cloudflare worker doesn't store anything and only serves as a proxy.


The playground has two ways of compiling Squint Clojurescript to JS: the normal ES6 mode and REPL-mode. In REPL-mode you're able to incrementally evaluate squint snippets. This works by compiling vars in keys of global objects, much like CLJS does it. E.g.:

(defn foo [])

is compiled to

var squint_core = await import('squint-cljs/core.js');
globalThis.user = globalThis.user || {}; = (function () {
return null;
var foo =;

in REPL-mode. This output certainly isn't optimal for JS bundlers like esbuild so it's only intended for development.

By hitting "Compile" the whole editor is compiled + evaluated. The compiled JavaScript is visible in the right output pane. When in REPL-mode, hitting Cmd-Enter (or Windows-Enter) with the cursor after a form will compile only that expression. Use the comment form to evaluate sub-expressions while working towards a complete solution.

While working on your puzzle, the state of the editor is saved to local storage, so if you accidentally close the browser, the input re-appear next time you visit the playground.

Let me know if you're enjoying this and feel free to post issues in the #squint channel on Clojurians Slack!

Published: 2023-11-24

Tagged: clojure squint