Posts tagged Clojure

Here are my notes about being puzzled about some Clojure code and diving into the implementation to figure it out. Although I figured it out the hard way, the exploration turned out to be interesting for me.

Yesterday a couple people asked me, “How and why do you use macros in a Lisp like Racket or Clojure?”.

I gave answers like:

• The compiler can do a search-and-replace on your code.

• You can make DSLs.

• They’re an “API for the compiler”.

Although all true, I wasn’t sure I was getting the full idea across.

So I’ve fallen behind on the blogging, for a few reasons. Time to catch up.

I’m calling this “day 5” as a useful fiction. It’s a distillation of what is closer to days 5–7, or something like that.

As I mentioned before, this series of blog posts is going more directly from brain to web. Reflection and editing? Not so much.

Overview:

• Spent time with Clojure Cookbook.
• Started a cheat sheet for Racket ↔ Clojure.
• Looked at split-with.
• Started a port of wffi from Racket to Clojure.
• Confusion: Aggregates and generics.

Please see the usual disclaimers from my previous posts.

As I mentioned yesterday, my next toy project is to write wrappers libraries for the new Hacker News API. This seems like a good exercise because the REST API is very simple, and I have experience doing this sort of thing in Racket. In fact, I’ll do the same thing in both Racket and Clojure.

The result is clacker-news and racker-news. Trademark registration application is in-process.¹

As with yesterday’s post, important disclaimers:

• I’ve used Racket heavily but not Clojure.

• Opinions expressed herein are not those of my employer, were I to have one.

• If indignation lasts more than four hours, please seek medical attention.

Day 2 with Clojure was much more fun! I didn’t hit speed bumps with tooling and workflow, so frequently. I was able to focus mostly on the code itself, which was wonderful.

For a slightly more realistic task, I decided to make a really simple function that, given a URL, would make a GET request and return the value of the Server response header (if any), and a list of URLs found on the page that are for other servers. The idea being, you could crawl from some starting point and accumulate some data about web server technology.

Until now, Clojure has been an “armchair” language for me. I’ve read a lot about it, and I’ve read a fair amount of code written in it. But aside from typing a few things into an online REPL like Try Clojure, I’ve not really used it hands-on.

A couple days ago I started my 12-week batch at Hacker School. First on my list is to get some real experience with Clojure.

And I’m going to blog about the experience.

Although I prefer Racket, there are a few idioms from Clojure I like. I’m particularly infatuated with the threading macros, -> and ->>.

I was surprised how little documentation I could find for these. So although I’m writing this for Racketeers, it’s possible a few Clojure folks might find it interesting, too.