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Interesting bits of life

Moldable Emacs: finding examples of Clojure functions (with tests)

Too long; didn't read

Check how to use the Clojure function under your cursor. Here we peek into the tests and render examples in an Org mode buffer.

The problem

I love good docs for functions! At my previous job, engineers followed the principle of keeping comments to a minimum. The idea is that tests should document usage. So, I needed to make the best of Emacs' navigation. I would both look at tests and the implementation of a symbol. The best tools for doing that in Scala projects were projectile and lsp-metals. Now I am about to start a new Clojure job (excited), and I have already polished my cider and cljr skills. Still, I thought: how could I make my gathering of examples simple?

It is a problem indeed

Actually, having a way to gather examples easily would be ideal for any programming I do. This was true for Scala work, Elisp editing and any language I worked with. About always, it helps me to read the name of a function and a series of assertions like (x 1 2) = 3, (x 3 2) = 5 to guess what the function does. Wouldn't be amazing if we could turn Emacs in an example giver for any language?

And there is a solution

This sounds material for a mold! We look at a function and want to see only its examples. This problem is about transforming the (Clojure) project in data we can filter to get what we need.

Here I will show only a naive way to solve this. This satisfies me for now, but I bet I will improve it later (e.g., using metadata and docs).

Anyway, let's start! Here a video to show you what I got to.

When my cursor is on a Clojure function, I can search for all the examples in the respective test file. I can then pick the one I need and navigate to the test file (if I wish to). The example project I am using is the awesome code-maat.

First, how do you find a "respective test file"? Easy: projectile!

(projectile-find-matching-test (buffer-file-name))

If there is a test file for the current open file, this will find (as long as your language is supported by projectile).

Next we want to find the name of the function at point.

(--> (list-at-point)
     (when (and it (> (length it) 3) (equal (nth 0 it) 'defn)) (nth 1 it))
     (symbol-name it))

The list-at-point works for all Lisps! Here I filter for only public Clojure functions (so no defn-). I could so generalize this, but maybe later (and if anybody needs it).

Finally how do you get the examples? Well emacs-tree-sitter to the rescue!

(--> (me/by-type 'list_lit self)
  (--filter (and
             (s-starts-with-p "(is(=" (s-replace " " "" (plist-get it :text)))
             (s-contains-p "of-module" (plist-get it :text)))

This was me exploring how to do it in a Playground mold. The variable self contains the flattened list of all tree-sitter nodes for the test file. I am looking only for clojure.test assertions (again I need to generalize to other test frameworks) and only for those mentioning my function (note the hard-coded "of-module": prototyping yuhuu!!!).

With these 3 bits we have the core of our mold. A bit of formatting in an Org buffer and we have easy to read examples!

I already crave to extend this to Clojure property testing! Let's see how it goes :)


The moral of this post is once again: make useful information easy to obtain! A software project is full of it. We can use this information to make easier to extend the project itself. I wrote about this a lot with my code-compass work, and I shall write even more for moldable-emacs. So if you are curious, gather examples of your favourite (tested) Clojure function (by trying out moldable-emacs -- if it is not easy to install ping me, I will fix it)!

Happy coding!