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The Lambda Island Blog

Making nREPL and CIDER More Dynamic (part 2)

By Arne Brasseur

In part 1 I set the stage with a summary of what nREPL is and how it works, how editor-specific tooling like CIDER for Emacs extends nREPL through middleware, and how that can cause issues and pose challenges for users. Today we’ll finally get to the “dynamic” part, and how it can help solve some of these issues.

To sum up again what we are dealing with: depending on the particulars of the nREPL client (i.e. the specific editor you are using, or the presence of specific tooling like refactor-clj), or of the project (shadow-cljs vs vanilla cljs), certain nREPL middleware needs to present for things to function as they should. When starting the nREPL server you typically supply it with a list of middlewares to use. This is what plug-and-play “jack-in” commands do behind the scenes. For nREPL to be able to load and use those middlewares they need to be present on the classpath, in other words, they need to be declared as dependencies. This is the second part that jack-in takes care of.

This means that nREPL servers are actually specialized to work with specific clients, which is a little silly if you think about it. You can’t connect with vim-iced to a server that expects CIDER clients, or at least not without reduced functionality.

Instead what we want is for the nREPL server to be client-agnostic. Once a client connects it can then tell the server of its needs, and “upgrade” the connection appropriately. It can even upgrade the connection incrementally, loading support for extra operations when it first needs them.

Let’s unpack what is needed to make this a reality, we need to be able to

  • add extra middleware to a running server or connection
  • add entries to the classpath at runtime
  • resolve and download (transitive) dependencies

Add Middleware to a Running Server

Turns out this problem has already been solved! Yay! Over a year ago Shen Tian implemented a dynamic-loader middleware (see nrepl/nrepl#185), which provides an add-middleware operation.

(-->
  id         "23"
  op         "add-middleware"
  session    "33d052f6-04dd-4f0e-916f-ed94aa0188ec"
  time-stamp "2021-11-19 09:40:42.092185482"
  middleware ("cider.nrepl/wrap-apropos" "cider.nrepl/wrap-classpath" "cider.nrepl/wrap-clojuredocs" "cider.nrepl/wrap-complete" "cider.nrepl/wrap-content-type" "cider.nrepl/wrap-debug" "cider.nrepl/wrap-enlighten" "cider.nrepl/wrap-format" "cider.nrepl/wrap-info" "cider.nrepl/wrap-inspect" "cider.nrepl/wrap-macroexpand" "cider.nrepl/wrap-ns" "cider.nrepl/wrap-out" "cider.nrepl/wrap-slurp" "cider.nrepl/wrap-profile" "cider.nrepl/wrap-refresh" "cider.nrepl/wrap-resource" "cider.nrepl/wrap-spec" "cider.nrepl/wrap-stacktrace" "cider.nrepl/wrap-test" "cider.nrepl/wrap-trace" "cider.nrepl/wrap-tracker" "cider.nrepl/wrap-undef" "cider.nrepl/wrap-version" "cider.nrepl/wrap-xref")
)
(<--
  id         "23"
  session    "33d052f6-04dd-4f0e-916f-ed94aa0188ec"
  time-stamp "2021-11-19 09:40:42.958165047"
  status     ("done")
)

If you are a CIDER user and are fairly up-to-date (this may require using master) you can try this out today.

(add-hook 'cider-connected-hook #'cider-add-cider-nrepl-middlewares)

Install this hook, then connect to a vanilla nREPL server. You can run one in your project with:

clojure -Sdeps '{:deps {nrepl/nrepl {:mvn/version "RELEASE"}}}' -M: -m nrepl.cmdline

However, chances are you’ll see something like this in the cider-repl buffer:

WARNING: middleware cider.nrepl/wrap-trace was not found or failed to load.
WARNING: middleware cider.nrepl/wrap-macroexpand was not found or failed to load.
WARNING: middleware cider.nrepl/wrap-inspect was not found or failed to load.
...

That’s because the dynamic-loader middleware tries to (require 'cider.nrepl), and fails. We need to first get cider-nrepl onto the classpath.

Adding Entries to the Classpath at Runtime

I have written at great length recently about the classpath and classloaders, (see The Classpath is a Lie). Simply adding entries to the classpath is fairly easy, Clojure’s DynamicClassLoader has a public addURL method. dynapath provides an abstraction around this. You need a few lines of code to check if you have the right kind of classloader, and if not instantiate a new one, and you’re good.

The harder part is controlling which classloader is in use at the point where require gets called. Typically this is the “context classloader”, which is a mutable thread local variable. As if mutability alone wasn’t tricky enough. Inside an nREPL request you’re generally covered, since nREPL creates a DynamicClassLoader for you for each session. It used to be a little too eager about creating new classloaders, which I addressed in nrepl/nrepl#248. However there is still the issue mentioned in The Classpath is a Lie, which is that clojure.main creates a new DynamicClassLoader for each call to repl, which in nREPL means on every eval. We do some recursing to find the DynamicClassLoader which sits directly above the system classloader, and use that. This tends to give fairly predictable results. There has been talk of forking clojure.main/repl for nREPL’s use, which would allow us to get rid of this annoying behavior, which would help simplify things.

To try this at home first find the location of the cider-nrepl JAR. This is a fat jar, it includes all its dependencies inlined and shaded with MrAnderson, so we don’t need to worry about resolving transitive dependencies.

find ~/.m2 -name 'cider-nrepl-*.jar'

Now we end up with something like this.

;; remove the previous one if necessary
(pop 'cider-connected-hook)

;; install the new hook
(add-hook 'cider-connected-hook
          (lambda ()
            (cider-sync-tooling-eval
             (parseedn-print-str
              '(.addURL (loop ; shenanigans to find the "root" DCL
                         [loader (.getContextClassLoader (Thread/currentThread))]
                         (let [parent (.getParent loader)]
                           (if (instance? clojure.lang.DynamicClassLoader parent)
                               (recur parent)
                             loader)))
                        (java.net.URL. "file:/home/arne/.m2/repository/cider/cider-nrepl/0.27.2/cider-nrepl-0.27.2.jar"))))
            (cider-add-cider-nrepl-middlewares)))

And there you go, you’ve successfully turned a vanilla nREPL connection into a cider-nrepl connection. You can now make full use of CIDER’s capabilities!

Resolving Dependencies

The previous solution assumes that you already have cider-nrepl*.jar on your system, that you know where to find it, that it matches the CIDER version Emacs is using (or at least is compatible, they no longer need to match exactly), and that it doesn’t need any additional dependencies.

A more generic solution would allow you to simply provide dependency coordinates, the type you supply in deps.edn or project.clj, and let Clojure figure out and download what it needs. Something like this:

(add-hook 'cider-connected-hook
          (lambda ()
            (cider-sync-tooling-eval
             (parseedn-print-str
              `(update-classpath! ((cider/cider-nrepl . ,cider-injected-nrepl-version)))))
            (cider-add-cider-nrepl-middlewares)))

This is called “dependency resolution”. It means taking a set of artifact-name+version coordinates, trying to find the given versions in one or more repositories (like Clojars or Maven Central), downloading their .pom files to figure out any transitive dependencies (recursively), and finally downloading the actual jars.

This requires a good deal of machinery, machinery that is not present in every Clojure process out of the box. You could start your nREPL process with tools.deps.alpha as a dependency, or lean on other libraries that are lower-level (org.apache.maven, Aether), or higher level (lambdaisland/classpath, Pomegranate). In any case we need these to be declared and loaded at boot time, if they are not present than we have a chicken-and-egg problem, our connection upgrade is once again blocked.

It’s also worth pointing out that this is by far the most complicated part of this whole endeavor. Adding tools.deps.alpha adds about 11MB of dependencies. Maybe that’s fine, many apps will pull in hundreds of megabytes of dependencies, what’s a dozen more? Still, people often have good reasons to keep their dependencies to a minimum, so this is not a decision that nREPL can make for them.

But we can sidestep the issue, in the case of CIDER we only need to download a single jar. We can just do that and be done with it. In fact, CIDER already contains code to do just that:

(add-hook 'cider-connected-hook
          (lambda ()
            (cider-sync-tooling-eval
             (parseedn-print-str
              `(.addURL (loop
                         [loader (.getContextClassLoader (Thread/currentThread))]
                         (let [parent (.getParent loader)]
                           (if (instance? clojure.lang.DynamicClassLoader parent)
                               (recur parent)
                             loader)))
                        (java.net.URL. ,(concat "file:" (cider-jar-find-or-fetch "cider" "cider-nrepl" cider-injected-nrepl-version))))))
            (cider-add-cider-nrepl-middlewares)))

Alternatively we could shell out to a tool that can do this work for us. We actually have a lot of choice there at this point. There’s of course clojure (i.e. the Clojure CLI), but Babashka can do the same thing (bb clojure -Sdeps {} -Spath), and there’s deps.clj, available as standalone binaries, or as an Uberjar, which could be invoked in a separate process/JVM, or loaded onto the classpath and invoked from Clojure directly.

It would be neat to wrap this in a little library which looks for one of these executables in some default places, and falls back to downloading deps.clj. This way you could get the functionality of a 11MB dependency for perhaps a hundred lines of Clojure, although this may seem like an unsavory approach to some.

It’s probably clear by now that there’s more than one way to shear a sheep, and you may be wondering why we don’t just go and hide all these details behind a facade that Just Works™. To an extent that will probably happen, these are early days and we are still figuring out how to best fit these pieces together. But we’re also likely to find that there’s no one size that fits all, whether it’s all tools that build on nREPL, or all users of those tools.

In an upcoming blog post I’ll be talking a lot more about Mechanisms vs Policies. I think at this point it’s ok to focus on the mechanisms, make sure we have the individual ingredients, and let people experiment with combining them in the way that makes most sense to them and their project.

Speaking of ingredients, there’s one more piece we haven’t covered yet, the Sideloader!

The Role of the Sideloader

Besides implementing the dynamic-loader middleware, Shen Tian also implemented another nREPL piece, meant to complement it, the Sideloader. Inspired by a similar mechanism in unrepl, the Sideloader is a special kind of ClassLoader which requests the resources it needs from a connected nREPL client.

The way this works is that the client first installs the sideloader by invoking the sideloader-start op. Now every time you require a namespace, access an io/resource, or load a Java class, the nREPL client (i.e. your editor) gets a sideloader-lookup message. If it is able to provide the requested resource, then it responds by sending a sideloader-provide message back.

The idea is that instead of adding cider-nrepl to the classpath directly, we let CIDER (Emacs) supply each namespace or resource to nREPL on demand, over the network.

I’ve put considerable effort into the client side implementation of this, see clojure-emacs/cider#3037, and the half a dozen PRs linked from there. This is why the aforementioned cider-jar-find-or-fetch exists, we download the cider-nrepl JAR from Emacs, so that we can supply its contents piecemeal to the Clojure process.

You can try this out as well:

(add-hook 'cider-connected-hook #'cider-upgrade-nrepl-connection)

This will enable the sideloader, and inject the necessary middleware as before.

So far I find the results rather underwhelming. Doubly so when connecting to an nREPL server on a different machine, which is the use case where this approach would actually make the most sense. Round-tripping over the network, and extracting file contents from the JAR from Emacs Lisp, then base64 encoding and decoding them to go over the wire… it all adds a lot of overhead. Note that this impacts all classloader lookups, since we only fall back to the system classloader when the Sideloader has determined that CIDER is unable to supply the given resource. It’s also worth nothing that for every .clj file that needs to be loaded this way, we round-trip three times: once to look for an __init.class file, once for a .cljc, and only then does Clojure look for the .clj file.

There are two obvious ways to improve this, one is to only have the sideloader active for a limited amount of time. You activate it, inject the necessary middleware, and turn it back off. Currently this does not work because of cider-nrepl’s deferred middleware. Most middleware only gets required the first time it is actually used, at which point the sideloader has long been disabled.

What I’ve also experimented with is providing a list of prefixes, so that only cider-nrepl’s namespaces are fetched via the sideloader, it helps of course, but the results are still underwhelming.

So as it stands I’m not convinced the sideloader is going to be an important piece in making this dynamic upgrading of nREPL connections a reality. I think the approaches I’ve set out above, where we make sure any resources required are present on the classpath directly, are much to be preferred. Faster and more reliable.

I do however think the Sideloader could become a cool piece of kit for loading files from the user’s code base, especially when connected to a remote process.

I run a Minecraft server on a cloud instance, and use witchcraft-plugin to endow Minecraft with Clojure superpowers, including an nREPL server. Locally I have my cauldron repo where I do my Minecraft creative coding. It’s a collection of repl sessions, and of namespaces with utility functions. When I eval (require 'net.arnebrasseur.cauldron.structures) then that currently fails, because this Cauldron repo isn’t present on the server. I need to go into each namespace I need and manually eval them in topological order before I can use them. Not great. In this case I think it would be fantastic if CIDER could spoon feed the server the necessary namespaces on request.

Conclusion

With this post I hope to draw some attention to all the work that’s been happening. We’ve been laying the groundwork for really improving the user experience, now we need to figure out how to bring it all together in a way that makes sense.

There’s a risk though that pushing for these changes will initially negatively impact the user experience, because change is hard, and we can’t anticipate everyone’s use case and needs.

So I expect “jack-in” to stay around, and to remain the default recommendation. It’s not perfect, but it works well for the vast majority of users.

At the same time we want to invite power users and tooling authors, especially those that have experienced the limitations and frustrations that come with the current approach, to consider these alternatives. To try them out and report back, so that we can shave off the rough edges, abstract away some of the plumbing, and gradually make this ready for broad consumption.

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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.

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Here’s a Clojure + Emacs life hack:

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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.

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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 REPL helper that you may like.

(defn trace! [v]
  (let [m    (meta v)
        n    (symbol (str (ns-name (:ns m))) (str (:name m)))
        orig (:trace/orig m @v)]
    (alter-var-root v (constantly (fn [& args]
                                    (prn (cons n args))
                                    (apply orig args))))
    (alter-meta! v assoc :trace/orig orig)))

(defn untrace! [v]
  (when-let [orig (:trace/orig (meta v))]
    (alter-var-root v (constantly orig))
    (alter-meta! v dissoc :trace/orig)))

Advent 2019 part 16, Coffee Grinders

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.

Over the last year or so I’ve found myself using some variations on a certain pattern when modelling processes in Clojure. It’s kind of like a event loop, but adapted to the functional, immutable nature of Clojure. For lack of a better name I’m calling these coffee grinders. (The analogy doesn’t even really work but the kid needs to have a name.)

Since I saw Avdi Grimm’s OOPS Keynote at Keep Ruby Weird last year I’ve been thinking a lot about the transaction vs process dichotomy. Avdi talks about the “Transactional Fallacy” from around 15:25. From his slides:

Advent 2019 part 15, jcmd and jstack

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.

Two shell commands anyone using JVM languages should be familiar with are jcmd and jstack. They are probably already available on your system, as they come bundled with the JDK. Try it out, run jcmd in a terminal.

This is what the result might look like

Advent 2019 part 13, Datomic Test Factories

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.

When I started consulting for Nextjournal I helped them out a lot with tooling and testing. Their data model is fairly complex, which made it hard to do setup in tests. I created a factory based approach for them, which has served the team well ever since.

First some preliminaries. At Nextjournal we’re big fans of Datomic, and so naturally we have a Datomic connection as part of the Integrant system map.

Advent 2019 part 12, Pairing in the Cloud with Tmux

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’m a strong believer in pair programming. It can be intense and exhausting, and its a skill you need to learn and get good at, but it’s extremely valuable. It improves knowledge sharing, prevents mistakes, and helps people to stay on track to make sure they are building the right thing, which is arguably one of the hardest aspects of our job.

But Gaiwan is a remote-first company. We are spread out across Germany, Brazil, Italy, and work with clients as far away as Singapore and Hong Kong, so we need good ways to pair remotely. For this we need a tool that is

Advent 2019 part 11, Integrant in Practice

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 been a fan of Integrant pretty much ever since it came out. For me there is still nothing that can rival it.

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)
  (greetings))

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 '(clojure.tools.namespace.repl/refresh)'
:reloading ()
:ok

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 clojure.java-time 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.

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.

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 npmjs.com.

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 lambdaisland.com. 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 java.net.URL, 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]
  [:div.view
   [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]
    [:div.view
     [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.