I’ve been getting questions from beginner Clojure developers on how to effectively use their REPL and interactive development. Quite a few of these people are coming from languages like Java, where they would have to compile their application and wait before running any code. Integrate your REPL with your editor You must have your REPL integrated with your editor. Whether that’s a text editor like emacs with cider, or an IDE like IntelliJ with Cursive, you have to be able to evaluate code in your REPL from the editor. Read more...

Last year, I submitted a PR to the Clojure web request routing library, Compojure. Even though I was doing Clojure full time at work, there was still a lot for me to learn and always will be. Opening a PR for an open source library I was familiar with and used all the time made me realize a few things: I didn’t know it as intimately as I thought I did. Read more...

Checking For An Empty List Don’t use (not (empty? coll)). Instead prefer (seq coll) instead. Seq returns nil if the collection is empty. If the seq isn’t empty then it returns a seq on that collection. Flattening The Result Of A Map By One Level If the result of a map function ever returns a list of lists, then use mapcat over (apply (concat (map...))): (map list (range 10)) ;; => ((0) (1) (2) (3) (4) (5) (6) (7) (8) (9)) (mapcat list (range 10)) ;; => (0 1 2 3 4 5 6 7 8 9) Maps Are Functions Maps, like keywords, are functions. Read more...

A lot of people have already heard that they should use Stuart Sierra’s component library to manage state in their Clojure applications. But most don’t know why and how you would incorporate it into your software. This how to guide will give you all the tools you need to start managing state in your Clojure software. What is component? Component is a Clojure library that can be thought of as a micro dependency injection framework. Read more...

Backstory I wrote an article on how I decided to go with Ruby instead of Clojure a while back. I moved my blog from Wordpress to Jekyll yesterday and think it’s time for an honest update. I also have a Node.js and Clojure comparison article if you’re also interested. It tells a different side of a similar story for people looking to pick between Javascript and Clojure. Performance and Speed Clojure and Ruby is often an order of a magnitude faster than Ruby for compute based tasks. Read more...

When developing applications in Clojure, one thing you might need is to be able to somehow keep different settings for each environment. For instance, you might want to be able to have different database settings for each environment. This can be achieved with leiningen profiles: ```clojure :profiles {:dev-overrides {} :dev [:dev-overrides {:dependencies [[com.cemerick/austin "0.1.5"] [com.cemerick/piggieback "0.1.4-SNAPSHOT"] [ring-mock "0.1.5"]] :plugins [[com.keminglabs/cljx "0.5.0"] [com.cemerick/austin "0.1.5"] [lein-cljsbuild "1.0.3"]]}] :test-overrides {} :test [:dev :test-overrides]} ``` Assuming you have that :profiles sub-map somewhere in your project. Read more...

I haven't had many good ideas for blog posts, but I've gotten this bright idea to do tutorials/overviews of the libraries I use in Clojure. The first one is Prismatic's Schema. Schema is an awesome library once you understand it. Let's go over some of the more important concepts via the schema readme. The first thing that jumps out when you first see Schema is that it allows you to validate functions and data. Read more...

I recently added the function juxt to my toolbox in Clojure. A good pattern I've discovered is using juxt to perform operations on a data structure and destructuring its return value. ```clojure (defn read-files [^String path] (let [data-files (find-data-files path) [prices receipts] ((juxt find-prices-file find-receipt-files) data-files)] {:prices (read-prices prices) :receipts (apply merge (read-receipts receipts))})) ```

Before we begin, make sure you can start a node.cljs repl first. One important thing I want to highlight is that you should have a stable version of node 0.12.X as the linked wiki page says. Additionally, you want to make sure you have npm installed so you can install node packages later on. Finally, I'm also assuming that you already have Clojure and Clojurescript setup with Leiningen. Let's begin. Read more...

I ran into an issue like usual. This time it seemed simple. I wanted to refer to a record that I def'd in another namespace. The problem is, you can't just do a :require and :refer it in regular Clojure. However, in Clojurescript this is how you would do it. What you have to do is :import it. And the key trick to keep in mind when using :import on records and Clojure namespaces is that dashes are converted to underscores like packages in Java. Read more...