Simple and Happy; is Clojure dying, and what has Ruby got to do with it?

The past week or so a lot of discussion and introspection has been happening in the Clojure community. Eric Normand responded to my one year Lambda Island post with some reflections on the size and growth of the community.

And then Zack Maril lamented on Twitter: “I’m calling it, clojure’s dying more than it is growing”. This sparked a mega-thread, which was still raging four days later. A parallel discussion thread formed on Reddit. Someone asked if their were any Clojure failure stories. They were pointed at this talk from RubyConf 2016, which seemed to hit a lot of people right in the feels, and sparked a subthread with a life of its own.

Meanwhile Ray, one of the hosts of the defn podcast reacted to the original tweet: “I’m calling it: Clojure is alive and well with excellent defaults for productive and sustainable software development.” This sparked another big thread.

Finally @phillmv, the person who did the talk that sparked so much debate, wrote his own summary of the discussion while reiterating some of his points in a blog post: Simple Ain’t Easy, but Hard Ain’t Simple: Leaving Clojure for Ruby.

It was all a bit much to be honest, but if we care about a healthy and growing Clojure community then it’s important that we have these conversations. Let’s try to unpack some of the points that were raised.

Clojure is dying

This statement initially set fire to the whole debate, but there seems to be little proof that this is true. This ask HN thread about who’s using Clojure shows plenty of companies adopting it recently. The list of companies on mentions Amazon, Facebook, Deutsche Bank, eBay, PayPal, Oracle, ThoughtWorks, Red Hat, Salesforce, Walmart, and 271 others. Onyx raised 500’000$US in funding last year, and the Taiwanese government is using Clojure for its citizen participation platform.

The community Slack grew from just over 6000 to close to 10K members in the past 12 months. lists 432 meetup groups that mention Clojure. We could definitely use more Clojure conferences, but with 8 annual conferences worldwide there are already twice as many as a few years back, and most of them seem to be growing in size year on year.

One personal observation: at my first EuroClojure in Berlin in 2013, most people I spoke to were enthusiasts. They programmed Java or Ruby or C# at their day jobs, and were dreaming of landing a Clojure job one day. At last year’s EuroClojure in Bratislava it was the opposite, it seemed most people were doing Clojure professionally in some shape or form.

So it seems industry adoption has grown significantly, and continues to gather steam. Mindshare in the open source and developer enthusiast communities has grown more slowly, and it’s worthwhile asking why that is.

“Simple vs. Easy” vs. “Programmer Happiness”

What also hit the internet last week was David Nolen’s talk from GOTO 2017, Idée Fixe. It’s a great talk. In his casual style he delivers some great insights. The central theme of the talk is “fixed ideas” standing in the way of progress. By becoming fixed on ideas which worked in the past, we lose the openness of mind needed to come up with novel ideas, even when experience or a changing context demonstrate that these old ideas no longer serve us.

Much of last week’s debate has centered on AppCanary’s choice to move back to Ruby, after a bad experience trying to build their platform in Clojure, and so it was a lot of “Clojure vs Ruby”, both on a language level, and on a cultural and philosophical level. I have been doing Ruby since 2006 and Clojure since 2013, I spoke at Ruby and Clojure conferences, and I’m intimately familiar with both of these languages and communities. I have some feels about this, y’all.

Each of these has their most prominent mantra. For Clojure it’s “Simple vs. Easy”, while the Rubyist chant is “Optimized for Programmer Happiness”. What do these mean, really? And what are the blind spots, the things we are simply unable to see, because these fixed ideas are in the way?

Simple vs. Easy

At Strange Loop 2011 Rich Hickey delivered one of his classic talks, Simple Made Easy, which would have a lasting effect on the discourse around Clojure. In it he contrasts “simple” with “easy”. Simple is the opposite of complex, it is a measure of how entangled things are, of how much is folded and twisted into one. Simple software is focused, it does not interleave multiple concerns.

Easy is the opposite of hard, it is a measure of the effort required to perform a task. This is largely subjective, something we are familiar with requires less effort, and so is perceived as easy.

When the selling point of a framework is that you can “build a blog in 15 minutes”, or that a DSL “reads like English”, then you’re talking about ease. Ease helps us when initially writing code. It lets us move fast, and that is not undesirable.

In the longer run other aspects come to the foreground. Why is it that, as projects age, the speed of development tends to slow down? That it becomes harder to make changes? How do you build something non-trivial over time, while remaining confident in its quality and correctness?

For that you need to be able to reason about the system. Human minds can only juggle so many things at the same time, and because of this simplicity reigns supreme. We can become familiar with hard things and thus make them easy, but dealing with complexity will continue to hurt your brain. Years of practice won’t change that.

And so Rich’s assertion is that many balls of mud sprang from a focus on ease, while sweeping complexity under the mat. And so he decided to build a language based on those features that promote simplicity, and rejecting those that lead to complexity.

Mutable state intertwines everything it touches. Objects mix functionality and state. Variables add a dimension of time to any code that references them.

Contrast that with immutable values, which are always local in time and space; pure functions, which can be reasoned about in isolation; reference types which make the dimension of time explicit by separating values from identities.

Clojure is not designed to be hard, to the contrary, I think a lot of thought has gone into making it easy to use as well, but when ease and simplicity are at odds, then simplicity always wins.

Programmer Happiness

Ruby’s creator, Yukihiro Matsumoto (Matz for short), has stated repeatedly that Ruby is designed to make programmers happy.

The goal of Ruby is to make programmers happy. I started out to make a programming language that would make me happy, and as a side effect it’s made many, many programmers happy.

He doesn’t really spell out what those things are that make him happy, but we can gather some insight by looking at what he borrowed from other languages, and what he left out. What may surprise you is that, before creating Ruby, Matz’s primary language was Lisp. Perl and Python are also cited as major influences. He wanted to build a modern object oriented scripting language, more suitable for building large systems than Perl, which he considered a toy language, and more pervasively object-oriented than Python, and so he borrowed the object model from Smalltalk.

When it comes to modeling software Ruby comes closest to Smalltalk, while syntactically, Ruby feels more like Perl, once the favorite scripting language of hackers and tinkerers the world over. Perl is the brainchild of Larry Wall, by education a linguist. Perl is heavily inspired by natural language, it championed the idea that programming languages should be designed for the human doing the programming, not for the machine running the program. In his talk Perl, the first postmodern computer language, Larry says,

So, to drag the subject back to computers, one of the characteristics of a postmodern computer language is that it puts the focus not so much onto the problem to be solved, but rather onto the person trying to solve the problem. I claim that Perl does that, and I also claim that, on some level or other, it was the first computer language to do that.

Much of that talk goes into the contrast of a reductionist Modernism vs a more holistic postmodernism, it’s a fascinating read, I highly recommend it.

Modernism, as a form of Classicalism, was always striving for simplicity, and was therefore essentially reductionistic. That is, it tended to take things to pieces. That actually hasn’t changed much. It’s just that Modernism tended to take one of the pieces in isolation and glorify it, while postmodernism tries to show you all the pieces at once, and how they relate to each other.

This still hasn’t given us a clear sense of what is meant with “programmer happiness”, but I’ll venture that it has to do with approaching things in a natural, organic way. Designing a language that appeals to the analytic and the creative and emotional brain equally. A language that loosens the straightjacket and lets you express yourself freely. Ruby promotes humane interfaces

The essence of the humane interface is to find out what people want to do and design the interface so that it’s really easy to do the common case.

Even when picking up a library for the first time you can often guess method names without looking at the docs. It just “does what you would expect”. Some even add aliases. Would you like some is_a? or do you prefer instance_of?? It doesn’t matter, they do the exact same thing!

Fixed ideas

Is there any surprise that these two sides seem to be speaking past each other? It’s like they live in different worlds. How can a Clojurist wearing their “Simple vs Easy” sunglasses ever comprehend the joy of creation sparking in the heart of a Rubyist? And how do we explain to the Ruby programmer the beauty of functional code, of having code and data laid bare, nothing up the sleeve, nothing tucked under the covers, just plain values, endlessly flowing, when all they can see is boilerplate code and single letter variable names?

And yet each side has much to learn from the other, once we get past our fixed ideas.

“Simple Made Easy” has instilled in many minds the notion that simple and easy are two sides of a spectrum, that they are necessarily at odds. But simple/complex and easy/hard are separate dimensions. While there’s great merit in striving for simplicity, it would be a mistake to disregard ease. I think as Clojure programmers, as library authors, we have been too focused on the reductionist, on building solid parts. But it’s only when these parts come together and meet the real world that magic happens.

The real world is messy, it’s a complex tangle, a braiding of concerns and constraints. Dealing with that is why we are programmers, this is the real measure of our worth. At the heart of our systems we must strive for “simple”, but at the edges we must inspire, delight, make the impossible effortless. We must do this for our customers, and we must do this for our peers.

Every tool, every library forms an interface, a language that people must first master to convey their intent. Pay as much attention to designing these interfaces as you would designing their functional internals. This is the face with which your code looks upon the world. Make it smile with its eyes.

To quote Laozi,

People usually fail when they are on the verge of success.
So give as much care to the end as to the beginning;
Then there will be no failure.

And Rubyists, you too have something to gain from this exchange. Yes, you’ve been hearing for years of the benefits of immutable data, the elegance of pure functions. These are interesting ideas, but don’t just read about them, try them out, use them in anger, and pay attention to how this influences the resulting system. You can do this in Ruby, but it will be hard to break out of old habits, so instead I recommend picking up a simpler, functional language, Clojure, OCaml, Elixir, and putting it through its paces. Afterwards you’ll look at your Ruby projects with fresh eyes, and a new sense of where complexity comes from.

I’ll leave you with one more data point to ponder: Clojure has polymorphism, but it eschews concrete derivation. It has interfaces and protocols, but no inheritance chains. It’s not a design decision that gets put in the limelight much, but it is one I encourage you to study. This alone has tremendous impact on how maintainable systems are.


One interesting thing that surfaced in the debates is that while some describe the Clojure community as “incredibly friendly and helpful”, others describe it as hostile. Well, which one is it? Again I think it’s interesting to compare and contrast with the Ruby community.

From my experience, the average interaction on Clojure’s Slack, mailing lists or Github issues is polite and friendly. I see people tirelessly and patiently answering questions in the #beginners channel and elsewhere. People really want to help.

And yet it’s a very different vibe from what I see in the Ruby world. There people really go out of their way to be nice to each other. Github issues are accompanied by a bit more elaborate explanations, some emoji or animated gifs, because it’s a low bandwith medium and you really want to make sure the human on the other side doesn’t take things the wrong way. A phrase that was popular in the early days was “MINSWAN”, “Matz is Nice So We Are Nice”. It’s something that deeply permeates this community, it’s part of what made Rails Girls such a huge success, and it’s why I still love going to Ruby conferences. It’s a vibe that’s hard to beat.

There are trolls in Rubyland too, but they get called out immediately. There is very little tolerance for less than friendly behavior. Virtually every conference and meetup has, and enforces, a Code of Conduct. Being welcoming, especially to beginners, is an essential part of Ruby’s DNA. How to be and remain open and welcoming is an important part of the discourse.

Clojure is different, it’s a mixed bunch. There are old-school lispers, converted Java programmers, people coming from other dynlangs like Ruby or Python, and they all carry different expectations. If you’ve been active in open source for more than a decade you know that a thick skin was a basic requirement. Harsh interactions were par for the course. People do what they are used to, and without a guiding principle like MINSWAN it’s harder to call people out and hold everyone to higher standards.

In the Clojure world, as in Clojure code, brevity is considered a feature, but there’s a thin line between being concise, and being curt. People still try to be friendly and nice, but the dial isn’t turned up all the way to 11. This is painfully true when it comes to the official docs, which seem to be written for machines rather than humans, it shows in the error messages, and it shows in many small online interactions.

Languages that draw a younger, more homogeneous crowd: Elm, Elixir, JavaScript, seem to be better at prioritizing the humanistic aspect. Both in the affordances of the software (Elm’s famous error messages), and in person-to-person interactions. I think we can, and should, take a leaf out of their book.

Catering for the Novice

People cite many pain points when coming to Clojure. Chas Emerick summarized it well:

✅ jvm pain
✅ docs/error msgs
✅ deployment pain
✅ tooling/debugging pain
✅ domain modeling difficulty

There’s truth in all of these, and we as a community will have to stand up if we want to change these, but I want to focus on one more thing in particular: meeting the needs of the absolute beginner.

The Dreyfus model distinguishes five levels of competence, from novice to mastery. At the absolute beginner level people execute tasks based on “rigid adherence to taught rules or plans”. Beginners need recipes. They don’t need a list of parts, or a dozen different ways to do the same thing. Instead what works are step by step instructions that they can internalize. As they practice them over time they learn the reasoning behind them, and learn to deviate from them and improvise, but they first need to feel like they’re doing something.

I have taught many people Ruby on Rails. Rails is tremendously complex (and complected), but it gets this part right. In a few sessions you can teach a person to create an interactive website backed by a database. It’s frustrating to teach because you’re walking a tight rope. Just follow the steps. Don’t peek under the covers. Don’t stare into the abyss. But that feeling of instantly being productive is what draws people in, what makes them think, “hey, maybe I can do this”.

People criticize this as optimizing the wrong thing. Yes, initial prototyping goes really fast, but long term maintainability suffers. This criticism isn’t without merit, but it tends to overlook this important aspect. “The Rails Way” provides a framework that makes teaching easy. It means you can just dive in and ignore all the peripheral stuff until later.

For ClojureBridge we tend to teach graphics programming with Quil, with Nightcode as the editor. There the experience is similar. Within the first hour people are doing stuff, they’re building things. And there are plenty of recipes out there for Quil that people can adopt and run with.

But in general, and for web development in particular, Clojure fails to deliver that experience. This may sound like a case for more of a “framework” and less of a “library” approach, but I think the bigger issue is documentation. We need more practical tutorials and how-to guides, that provide clear recommendations of tools and libraries to use, that explain things step by step, with empathy, with beginners in mind. Guides that you can follow from top to bottom and that actually work, even when you’re on Windows, or Linux, or have never heard of a classpath.

We’re also missing a dialogue about how to program, both in the small: how do you structure a function, what are common idioms, how do you manipulate data structures; and in the large: doing domain modeling, architecting systems, designing interfaces. Ruby folks talk about these things all the time, but talks like these are eerily absent from Clojure conferences, and yet it’s something people consistently cite as a stumbling block.

If we want Clojure to continue to grow, we need to take responsibility for how it is perceived. Clojure is not always perceived as a friendly language. We can retort, “it was very friendly to me”, or we can listen without interrupting the speaker, believe they are speaking from good faith, and do better.

🡅 You can comment (and upvote) on

Update: The web site has a guide section for tutorials and guides and accepts pull requests.

Many thanks to Chas Emerick, Eric Normand, and Tobias Pfeiffer for reviewing an earlier version of this article.

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The recently released clip by the folks from Juxt does deserve an honorable mention. It has an interesting alternative approach which some may prefer, but it does not resonate with me. I prefer my system configuration to be just data, rather than code wrapped in data.

Advent 2019 part 10, Hillcharts with Firebase and Shadow-cljs

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

Recently I led a workshop for a client to help them improve their development process, and we talked a lot about Shape Up, a book released by Basecamp earlier this year that talks about their process. You can read it for free on-line, and I can very much recommend doing so. It’s not a long read and there are a ton of good ideas in there.

One of these ideas has also become a feature in Basecamp, namely hill charts. These provide a great way to communicate what stage a piece of work is in. Are you still going uphill, figuring things out and discovering new work, or are you going downhill, where it’s mostly clear what things will look like, and you’re just executing what you discovered?

Advent 2019 part 9, Dynamic Vars in ClojureScript

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

Clojure has this great feature called Dynamic Vars, it lets you create variables which can be dynamically bound, rather than lexically. Lexical (from Ancient Greek λέξις (léxis) word) in this case means “according to how it is written”. let bindings for instance are lexical.

(defn hello [x]
  (str "hello " x))

(defn greetings []
  (str "greetings" foo)) ;; *error*

(let [foo 123]
  (hello foo)

Advent 2019 part 8, Everything is (not) a pipe

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

I’ve always been a big UNIX fan. I can hold my own in a shell script, and I really like the philosophy of simple tools working on a uniform IO abstraction. Uniform abstractions are a huge enabler in heterogenous systems. Just think of Uniform Resource Locators and Identifier (URLs/URIs), one of the cornerstones of the web as we know it.

Unfortunately since coming to Clojure I feel like I’ve lost of some of that power. I’m usually developing against a Clojure process running inside (or at least connected to) my trusty editor, and the terminal plays second fiddle. How do I pipe things into or out of that?

Advent 2019 part 7, Do that doto

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

doto is a bit of an oddball in the Clojure repertoire, because Clojure is a functional language that emphasizes pure functions and immutabilty, and doto only makes sense when dealing with side effects.

To recap, doto takes a value and a number of function or method call forms. It executes each form, passing the value in as the first argument. At the end of the ride it returns the original value.

Advent 2019 part 6, A small idiom

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

As an avid tea drinker I’ve been poring (pouring?) over this catalog of teas.

(def teas [{:name "Dongding"
            :type :oolong}
           {:name "Longjing"
            :type :green}
           {:name "Baozhong"
            :type :oolong}
           {:name "Taiwan no. 18"
            :type :black}
           {:name "Dayuling"
            :type :oolong}
           {:name "Biluochun"
            :type :green}])

Advent 2019 part 5, Clojure in the shell

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

I already showed you netcat, and how it combines perfectly with socket REPLs. But what if all you have is an nREPL connection? Then you use rep

$ rep '('
:reloading ()

Advent 2019 part 4, A useful idiom

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

Here’s a little Clojure idiom that never fails to bring me joy.

(into {} (map (juxt key val)) m)

Advent 2019 part 3, `every-pred` and `some-fn`

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

Ah clojure.core, it’s like an all you can eat hot-pot. Just when you think you’ve scooped up all it has to offer, you discover another small but delicious delicacy floating in the spicy broth.

In exactly the same way I recently became aware of two functions that until now had only existed on the periphery of my awareness. I’ve since enjoyed using them on several occasions, and keep finding uses for them.

Advent 2019 part 2, Piping hot network sockets with Netcat

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

Part of what I want to do in this series is simply point at some of the useful tools and libraries I discovered in the past year. I’ve adopted a few tools for doing network stuff on the command line which I’ll show you in another post. First though we’ll look at a classic: netcat!

I’ve been using netcat for years, it’s such a great tool. It simply sets up a TCP connection and connects it to STDIN/STDOUT. Pretty straightforward. I’ve been using it more and more though because of Clojure’s socket REPL.

Advent 2019 part 1, Clojure Vocab: to Reify

This post is part of Advent of Parens 2019, my attempt to publish one blog post a day during the 24 days of the advent.

An interesting aspect of the Clojure community, for better or for worse, is that it forms a kind of linguistic bubble. We use certain words that aren’t particularly common in daily speech, like “accretion”, or use innocuous little words to refer to something very specific. Even a simple word like “simple” is no longer that simple.

We can thank Rich Hickey for this. He seems to care a great deal about language, and is very careful in picking the words he uses in his code, documentation, and in his talks.

Advent of Parens 2019

Ah, the advent, the four weeks leading up to Christmas. That period of glühwein and office year-end parties.

The last couple of years I’ve taken part in the Advent of Code, a series of programming puzzles posted daily. They’re generally fun to do and wrapped in a nice narrative. They also as the days progress start taking up way too much of my time, so this year I won’t be partaking in Advent of Code, instead I’m trying something new.

From the first to the 24th of December I challenge myself to write a single small blog post every day. If my friend Sarah Mirk can do a daily zine for a whole year, surely I can muster a few daily paragraphs for four weeks.

Lambda Island Streaming Live this Thursday and Friday

We are definitely back from holidays, and to demonstrate that we’re not just doing one but two live stream events!

Felipe and Arne pairing

Thursday 5 September, 13:00 to 15:00 UTC

Fork This Conference

Last weekend Heart of Clojure took place in Leuven, Belgium. As one of the core organizers it was extremely gratifying to see this event come to life. We started with a vision of a particular type of event we wanted to create, and I feel like we delivered on all fronts.

For an impression of what it was like you can check out Malwine’s comic summary, or Manuel’s blog post.

It seems people had a good time, and a lot of people are already asking about the next edition. However we don’t intend to make this a yearly recurring conference. We might be back in two years, maybe with another Heart of Clojure, maybe with something else. We need to think about that.

Advice to My Younger Self

When I was 16 I was visited by a man who said he had come from the future. He had traveled twenty years back to 1999 to sit down with me and have a chat.

We talked for an hour or so, and in the end he gave me a few pieces of advice. I have lived by these and they have served me well, and now I dispense this advice to you.

Become allergic to The Churn

ClojureScript logging with goog.log

This post explores goog.log, and builds an idiomatic ClojureScript wrapper, with support for cljs-devtools, cross-platform logging (by being API-compatible with Pedestal Log), and logging in production.

This deep dive into GCL’s logging functionality was inspired by work done with Nextjournal, whose support greatly helped in putting this library together.

Clojure’s standard library isn’t as “batteries included” as, say, Python. This is because Clojure and ClojureScript are hosted languages. They rely on a host platform to provide the lower level runtime functionality, which also allows them to tap into the host language’s standard library and ecosystem. That’s your batteries right there.

The Art of Tree Shaping with Clojure Zippers

This is a talk I did for the “Den of Clojure” meetup in Denver, Colorado. Enjoy!

Captions (subtitles) are available, and you can find the transcript below, as well as slides over here.

For comments and discussion please refer to this post on r/Clojure.

Test Wars: A New Hope

Yesterday was the first day for me on a new job, thanks to Clojurists Together I will be able to dedicate the coming three months to improving Kaocha, a next generation test runner for Clojure.

A number of projects applied for grants this quarter, some much more established than Kaocha. Clojurists Together has been asking people through their surveys if it would be cool to also fund “speculative” projects, and it seems people agreed.

I am extremely grateful for this opportunity. I hope to demonstrate in the coming months that Kaocha holds a lot of potential, and to deliver some of that potential in the form of a tool people love to use.

Two Years of Lambda Island, A Healthy Pace and Things to Come

It’s been just over two years since Lambda Island first launched, and just like last year I’d like to give you all an update about what’s been happening, where we are, and where things are going.

To recap: the first year was rough. I’d been self-employed for nearly a decade, but I’d always done stable contracting work, which provided a steady stream of income, and made it easy for me to unplug at the end of the day.

Lambda Island was, as the Dutch expression goes, “a different pair of sleeves”. I really underestimated what switching to a one-man product business in a niche market would mean, and within months I was struggling with symptoms of burnout, so most of year one was characterised by trying to keep things going and stay afloat financially, while looking after myself and trying to get back to a good place, physically and mentally.

D3 and ClojureScript

This is a guest post by Joanne Cheng (twitter), a freelance software engineer and visualization consultant based in Denver, Colorado. She has taught workshops and spoken at conferences about visualizing data with D3. Turns out ClojureScript and D3 are a great fit, in this post she’ll show you how to create your own visualization using the power of D3 and the elegance of ClojureScript.

I use D3.js for drawing custom data visualizations. I love using the library, but I wanted to try one of the several compile to JavaScript options, and I decided to look into ClojureScript. It ended up working out well for me, so I’m going to show you how I created a D3.js visualization using ClojureScript!

What we’re visualizing

Reloading Woes

Update: seems Stuart Sierra’s blog post has dropped off the internet. I’ve updated the link to refer to the Wayback Machine’s version instead.

Setting the Stage

When doing client work I put a lot of emphasis on tooling and workflow. By coaching people on their workflow, and by making sure the tooling is there to support it, a team can become many times more effective and productive.

The Bare Minimum, or Making Mayonnaise with Clojure

Making Mayonnaise

Imagine you have a grandfather who’s great at making mayonnaise. He’s been making mayonnaise since before the war, and the result is truly excellent. What’s more, he does this with a good old fashioned whisk. He’s kept his right arm in shape throughout decades just by beating those eggs and oil and vinegar.

Now he’s bought himself a handheld electric mixer after hearing his friend rave about hers, but after a few tries he gives up and goes back to his whisk. He says he just can’t get the same result. This seems slightly odd, so the next time you go over you ask him to show you how he uses the mixer.

Clojure Gotchas: "contains?" and Associative Collections

When learning a programming language we rarely read the reference documentation front to back. Instead someone might follow some tutorials, and look at sample code, until they’re confident enough to start a little project for practice.

From that point on the learning process is largely “just in time”, looking up exactly the things you need to perform the task at hand. As this goes on you might start to recognize some patterns, some internal logic that allows you to “intuit” how one part of the language works, based on experience with another part.

Developing this “intuition” — understanding this internal logic — is key to using a language effectively, but occasionally our intuition will be off. Some things are simply not obvious, unless someone has explained them to us. In this post I will look at something that frequently trips people up, and attempt to explain the underlying reasoning.

Dates in Clojure: Making Sense of the Mess

Update 2018-11-27: while most of this article is still relevant, I no longer recommend using JodaTime as the main date/time representation for new projects. Even existing projects that aren’t too invested in JodaTime/clj-time should consider migrating to java.time and across the board.

Update 2 2019-05-29: Also check out the talk Cross Platform DateTime Awesomeness by Henry Widd, given at Clojure/north 2019

You can always count on human culture to make programming messy. To find out if a person is a programmer just have them say “encodings” or “timezones” and watch their face.

Clojure Gotchas: Surrogate Pairs

tl;dr: both Java and JavaScript have trouble dealing with unicode characters from Supplementary Planes, like emoji 😱💣.

Today I started working on the next feature of lambdaisland/uri, URI normalization. I worked test-first, you’ll get to see how that went in the next Lambda Island episode.

One of the design goals for this library is to have 100% parity between Clojure and ClojureScript. Learn once, use anywhere. The code is all written in .cljc files, so it can be treated as either Clojure or ClojureScript. Only where necessary am I using a small amount of reader conditionals.

Loading Clojure Libraries Directly From Github

Did you ever fix a bug in an open source library, and then had to wait until the maintainer released an updated version?

It’s happened to me many times, the latest one being Toucan. I had run into a limitation, and found out that there was already an open ticket. It wasn’t a big change so I decided to dive in and address it. Just a little yak shave so I could get on with my life.

Now this pull request needs to be reviewed, and merged, and eventually be released to Clojars, but ain’t nobody got time for that stuff. No sir-ee.

Lambda Island Turns One, The Story of a Rocky Ride

One year ago to date I launched Lambda Island, a service that offers high quality video tutorials on web development with Clojure and ClojureScript. It’s been quite a ride. In this post I want to look back at the past year, provide some insight into how this experience has been for me, and give you a glimpse of what the future has in store.

This story really starts in December 2015. After three years of doing contract work for Ticketsolve I decided it was time for a change. I have been self-employed for many years, but I knew that sooner or later I wanted to try my hand at selling a product, rather than selling my time.

In January and February I took some time for soul-searching, and recharging. I went to speak at RubyConf Australia, and got to hang out with some old friends around Australia and New Zealand. Once back in Berlin I got busy creating Lambda Island.

Writing Node.js scripts with ClojureScript

In the two most recent  Lambda Island episodes I covered in-depth how to create command line utilities based on Lumo, how to combine them with third party libraries, and how to deploy them to

However there’s a different way to create tools with ClojureScript and distribute them through NPM, without relying on Lumo. In this blog post I want to quickly demostrate how to do just that.

To recap, Lumo is a ClojureScript environment based on Node.js, using bootstrapped (self-hosted) ClojureScript. This means the ClojureScript compiler, which is written in Clojure and runs on the JVM, is used to compile itself to JavaScript. This way the JVM is no longer needed, all you need is a JavaScript runtime to compile and run ClojureScript code, which in this case is provided by Node.js. On top of that Lumo uses nexe, so Lumo can be distributed as a single compact and fast executable binary.

Announcing lambdaisland/uri 1.0.0

I just released lambdaisland/uri, a pure Clojure/ClojureScript URI library. It is available on Github and Clojars.

This is a small piece of the code base that powers It’s inspired by Ruby’s Addressable::URI, the most solid URI implementation I’ve seen to date, although it only offers a small part of the functionality that library offers.

It’s written in pure Clojure/ClojureScript, with only minimal use of .cljc reader conditionals to smooth over differences in regular expression syntax, and differences in core protocols. It does not rely on any URI functionality offered by the host, such as, so it’s usable across all current and future Clojure implementations (Clojure, ClojureScript, ClojureCLR).

re-frame Subscriptions Got Even Better

Up until recently, to use re-frame subscriptions in Reagent views, you had to use a form-2 component.

A form-2 component is a function that returns another function, which does the actual rendering of the component to hiccup. In contrast, a form-1 component renders the hiccup directly.

;; form-1
(defn todo-item [todo]
   [todo-checkbox (:id todo) (:completed todo)]
   [:label {:unselectable "on"} title]
   [:button.destroy {:on-click #(dispatch [:todos/remove (:id todo)])}]])

;; form-2
(defn todo-item [todo]
  (fn [todo]
     [todo-checkbox (:id todo) (:completed todo)]
     [:label {:unselectable "on"} title]
     [:button.destroy {:on-click #(dispatch [:todos/remove (:id todo)])}]]))

Game Development with Clojure/ClojureScript

This weekend it’s Ludum Dare again, the world’s longest running game jam. The idea is that, alone or with a team, you build a game in a weekend based on a certain theme.

We got a little team together here in Berlin, and so I’ve been reviewing what options there are for someone wanting to build a game in Clojure or Clojurescript.

The good news is there are plenty of options, as you’ll see from the list below. You can do desktop games, browser based games with canvas or webgl, and you can even create Unity 3D games, all from your comfortable Clojure parentheses.

Union Types with Clojure.Spec

Elm and other statically typed languages have a great feature called Union Types (also called Sum Types or Algebraic Data Types).

Here’s an example taken from Elm. Suppose your system used to represent users as integers, maybe just an auto-incrementing primary key, but then switched to UUIDs represented as strings.

To correctly model this situation, you need a way to create a type that can be either an integer or a string, that’s what union types give you.