Clojure Gotchas: Surrogate Pairs

tl;dr: both Java and JavaScript have trouble dealing with unicode characters from Supplementary Planes, like emoji šŸ˜±šŸ’£.

Today I started working on the next feature of lambdaisland/uri, URI normalization. I worked test-first, youā€™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.

#?(:clj
   (defmethod print-method URI [this writer]
     (.write writer "#")
     (.write writer (str edn-tag))
     (.write writer " ")
     (.write writer (prn-str (.toString this))))

   :cljs
   (extend-type URI
     IPrintWithWriter
     (-pr-writer [this writer _opts]
       (write-all writer "#" (str edn-tag) " " (prn-str (.toString this))))))

Example of a reader conditional

For this feature however Iā€™m digging quite deeply into the innards of strings, in order to do percent-encoding and decoding. Once you get into hairy stuff like text encodings the platform differences become quite apparent. Instead of trying to smooth over the differences with reader conditionals, I decided to create two files platform.clj and platform.cljs. They define the exact same functions, but one does it for Clojure, the other for ClojureScript. Now from my main namespace I require lambdaisland.uri.platform, and it will pull in the right one depending on the target that is being compiled for.

(ns lambdaisland.uri.normalize
  (:require [clojure.string :as str]
            ;; this loads either platform.clj, or platform.cljs
            [lambdaisland.uri.platform :refer [string->byte-seq
                                               byte-seq->string
                                               hex->byte 
                                               byte->hex
                                               char-code-at]]))

The first challenge I ran into was that I needed to turn a string into a UTF-8 byte array, so that those bytes can be percent encoded. In Clojure thatā€™s relatively easy. In ClojureScript the Google Closure library came to the rescue.

;; Clojure
(defn string->byte-seq [s]
  (.getBytes s "UTF8"))

(defn byte-seq->string [arr]
  (String. (byte-array arr) "UTF8"))


;; ClojureScript
(require '[goog.crypt :as c])

(defn string->byte-seq [s]
  (c/stringToUtf8ByteArray s))

(defn byte-seq->string [arr]
  (c/utf8ByteArrayToString (apply array arr)))

To detect which characters need to be percent-encoded Iā€™m using some regular expressions. Things seemed to be going well, but when re-running my tests on ClojureScript I started getting some weird results.

;; Clojure
(re-seq #"." "šŸ„€")
;;=> ("šŸ„€")

;; ClojureScript
(re-seq #"." "šŸ„€")
;;=> ("ļæ½" "ļæ½")

Update: Ben Lovell (@socksy) pointed out that modern JavaScript has a flag you can add to regular expressions to make them unicode aware, like so: /some-regex/u. In ClojureScript you can use this syntax to achieve the same effect: (re-seq #"?(u)." "šŸ„€")

This, gentle folks, is the wonder of surrogate pairs. So how does this happen?

Sadly I donā€™t have time to give you a complete primer on Unicode and its historical mistakes, but to give you the short versionā€¦

JavaScript was created at a time when people still assumed Unicode would never have more than 65536 characters, and so its strings use two bytes to represent one character, always. This is known as the UCS-2 encoding.

Unicode has grown a lot since then, and now also has a lot of codepoints with numbers greater than 65536. These include many old scripts, less common CJK characters (aka Hanzi or Kanji), many special symbols, and last but not least, emoji!

So they needed a way to represent these extra characters, but they also didnā€™t want to change all those systems using UCS-2 too much, so UTF-16 was born. In UTF-16 the first 65536 codepoints are still encoded the same as in UCS-2, with two bytes, but the ones higher up are encoded with 4 bytes using some special tricks involving some gaps in the Unicode space. In other words, these characters take up the width of two characters in a JavaScript string. These two characters are known as a ā€œsurrogate pairā€, the first one being the ā€œhigh surrogateā€, and the other one the ā€œlow surrogateā€.

So this is what JavaScript strings do now, but the rest of the language never got the memo. Regular expressions, string operations like .substr and .slice all still happily assume itā€™s 1995, and so theyā€™ll cut surrogate pairs in half without blinking.

ClojureScript builds on those semantics, so you are liable to all the same mess.

(seq "šŸš© ")
;;=> ("ļæ½" "ļæ½")

I managed to work around this by first implementing char-seq, a way of looping over the actual characters of a string.

(defn char-code-at [str pos]
  #?(:clj (.charAt str pos)
     :cljs (.charCodeAt str pos)))

(defn char-seq
  "Return a seq of the characters in a string, making sure not to split up
  UCS-2 (or is it UTF-16?) surrogate pairs. Because JavaScript. And Java."
  ([str]
   (char-seq str 0))
  ([str offset]
   (if (>= offset (count str))
     ()
     (let [code (char-code-at str offset)
           width (if (<= 0xD800 (int code) 0xDBFF) 2 1)] ; detect "high surrogate"
       (cons (subs str offset (+ offset width))
             (char-seq str (+ offset width)))))))

I imagine this snippet might come in handy for some. Notice how itā€™s basically identical for Clojure and ClojureScript. This is because Java suffers from the same problem. The only difference is that there some of the language got the memo. So for instance regular expressions correctly work on characters, but things like substring or .charAt are essentialy broken.

Hopefully ClojureScript will eventually fix some of this mess, for instance by having a seq over a string return the real characters, but for performance reasons itā€™s likely they will want to stick closely to JavaScript semantics, so I wouldnā€™t count too much on this happening.

In the meanwhile what we can do is document the things you need to watch out for, and write cross-platform libraries like lambdaisland/uri that smooth over the differences. šŸ‘

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  (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.

Iā€™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 Iā€™ve lost of some of that power. Iā€™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 Iā€™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.

Hereā€™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, itā€™s like an all you can eat hot-pot. Just when you think youā€™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. Iā€™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. Iā€™ve adopted a few tools for doing network stuff on the command line which Iā€™ll show you in another post. First though weā€™ll look at a classic: netcat!

Iā€™ve been using netcat for years, itā€™s such a great tool. It simply sets up a TCP connection and connects it to STDIN/STDOUT. Pretty straightforward. Iā€™ve been using it more and more though because of Clojureā€™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 arenā€™t particularly common in daily speech, like ā€œaccretionā€, or use innocuous little words to refer to something very specific. Even a simple word like ā€œsimpleā€ 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 glĆ¼hwein and office year-end parties.

The last couple of years Iā€™ve taken part in the Advent of Code, a series of programming puzzles posted daily. Theyā€™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 wonā€™t be partaking in Advent of Code, instead Iā€™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 weā€™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 Malwineā€™s comic summary, or Manuelā€™s blog post.

It seems people had a good time, and a lot of people are already asking about the next edition. However we donā€™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 GCLā€™s logging functionality was inspired by work done with Nextjournal, whose support greatly helped in putting this library together.

Clojureā€™s standard library isnā€™t as ā€œbatteries includedā€ 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 languageā€™s standard library and ecosystem. Thatā€™s your batteries right there.

The Art of Tree Shaping with Clojure Zippers

This is a talk I did for the ā€œDen of Clojureā€ 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 ā€œspeculativeā€ 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

Itā€™s been just over two years since Lambda Island first launched, and just like last year Iā€™d like to give you all an update about whatā€™s been happening, where we are, and where things are going.

To recap: the first year was rough. Iā€™d been self-employed for nearly a decade, but Iā€™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, ā€œa different pair of sleevesā€. 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 sheā€™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 Iā€™m going to show you how I created a D3.js visualization using ClojureScript!

What weā€™re visualizing

Reloading Woes

Update: seems Stuart Sierraā€™s blog post has dropped off the internet. Iā€™ve updated the link to refer to the Wayback Machineā€™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 whoā€™s great at making mayonnaise. Heā€™s been making mayonnaise since before the war, and the result is truly excellent. Whatā€™s more, he does this with a good old fashioned whisk. Heā€™s kept his right arm in shape throughout decades just by beating those eggs and oil and vinegar.

Now heā€™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 canā€™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 theyā€™re confident enough to start a little project for practice.

From that point on the learning process is largely ā€œjust in timeā€, 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 ā€œintuitā€ how one part of the language works, based on experience with another part.

Developing this ā€œintuitionā€ ā€” understanding this internal logic ā€” 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 arenā€™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 ā€œencodingsā€ or ā€œtimezonesā€ and watch their face.

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: ā€œIā€™m calling it, clojureā€™s dying more than it is growingā€. 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: ā€œIā€™m calling it: Clojure is alive and well with excellent defaults for productive and sustainable software development.ā€ 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?

Itā€™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 wasnā€™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 ainā€™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. Itā€™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 recentĀ  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 thereā€™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. Itā€™s inspired by Rubyā€™s Addressable::URI, the most solid URI implementation Iā€™ve seen to date, although it only offers a small part of the functionality that library offers.

Itā€™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 itā€™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 itā€™s Ludum Dare again, the worldā€™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 Iā€™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 youā€™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).

Hereā€™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, thatā€™s what union types give you.