I was building VM images for Google Cloud with Packer, and provisioning them with Ansible. Everything had been working in the morning, but in the afternoon one computer wasn’t working after I had upgraded Ansible with Homebrew. I was having a really tough time figuring out why Ansible and Packer were running fine on one computer, and not on the other. I was getting the following error:

googlecompute: fatal: [default]: UNREACHABLE! => {"changed": false, "msg": "SSH Error: data could not be sent to remote host \"127.0.0.1\". Make sure this host can be reached over ssh", "unreachable": true}

Investigating the error, I found it could indicate any number of problems, as Ansible is masking the underlying SSH error.

After checking the versions of Python, Ansible, and Packer on the two computers, I found one difference. On the computer that wasn’t working, when running ansible --version it had a config file listed:

$ ansible --version
ansible 2.3.2.0
  config file = /Users/<user>/.ansible.cfg
  configured module search path = Default w/o overrides
  python version = 2.7.13 (default, Dec 18 2016, 07:03:39) [GCC     4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]

Opening that file:

$ cat ~/.ansible.cfg
[ssh_connection]
pipelining = True

I moved that file to another location so it wouldn’t be picked up by Ansible, and after rerunning Packer a second time, got this error:

googlecompute: fatal: [default]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Warning: Permanently added '[127.0.0.1]:62684' (RSA) to the list of known hosts.\r\nReceived disconnect from 127.0.0.1 port 62684:2: too many authentication failures\r\nAuthentication failed.\r\n", "unreachable": true}

I then used the extra_arguments option for the Ansible provisioner to pass [ "-vvvv" ] to Ansible. I ran this on both computers and diffed the output. I saw that the dynamically generated key was being successfully provided on the working computer (after one other local key). On the failing computer I had many SSH keys that were being tried before I could get to the dynamic key, and I was getting locked out.

SSH servers only allow you to attempt to authenticate a certain number of times (six by default). All of your loaded keys will be tried before the dynamically generated key provided to Ansible. If you have too many SSH keys loaded in your ssh-agent, the Ansible provisioner may fail authentication.

Running ssh-add -D unloaded all of the keys from my ssh-agent, and meant that the dynamic key Packer was generating was provided first.

I hope this is helpful to someone else, and saves you from hours of debugging!

Postscript

I was very confused by seeing that my computer was trying to connect to 127.0.0.1, instead of the Google Cloud Platform VM. My best guess is that Packer/Google Cloud SDK proxies the connection from my computer to the VM.

While working on Deps I wanted to detect the user’s time zone at signup, to localise the times that I presented to them. I hunted around and found a variety of libraries that offer time zone detection, like moment.js, and jstz. However I wasn’t keen on pulling in a dependency on one of these libraries if I could help it, so I kept looking. I also considered trying to detect the user’s time zone from their IP address using something like the Maxmind GeoIP database, and that probably would have been the method I settled on.

However in my research, just before I started with IP based detection, I found that there is a newish Internationalization API, which will give you the user’s system time zone.

Intl.DateTimeFormat().resolvedOptions().timeZone
=> "Pacific/Auckland"

All current browsers support the Internationalization API including IE11. However there is a slight wrinkle to keep in mind when using it: on some older browser versions that do support Internationalization (IE <=11, and Firefox <=51), the timeZone property is set to undefined rather than the user’s actual time zone. As best as I can tell, at the time of writing (July 2017) all current browsers except for IE11 will return the user’s actual timezone. If you do need to support older browser environments then you could look at moment.js. It uses the newer Internationalization API when it is available, and falls back to other heuristics if it isn’t. For my purposes, my browser statistics show almost no IE usage, so I chose to just use the newer method, while also allowing the user to manually update their time zone if they needed.

Bryan Cantrill on integrity. Edited slightly for clarity and profanity:

We are on a collision course with the Amazon Principles […] What is going on? I’m losing my mind. The wheels are off, everyone has to get out of the car and this is why. All of these [expletive] leadership principles, from all these organisations, where is integrity? Damn it where’s integrity? Amazon has 14 leadership principles and integrity is not on it. [That’s] inexcusable. I’m sorry, if you’ve got one principle in your organisation, its integrity? Right? […] No we’re living in a world that has lost it’s [expletive] mind, I don’t understand it. Why the appetite for territory? Do you not know where your next meal is coming from? Do you not have a roof over your head? I mean I’m sorry, I just don’t get it. We have got an incredible luxury. There’s never been a labour market like this one. Where have we so screwed up with a generation, if not a society where we’ve got people who are so extrinsically motivated? What the [expletive] is wrong with us? I mean its like how is integrity not the only thing you have?

[Andrew Clay Shafer]: Are we doing the full critique of capitalism today?

No it’s not. Bullshit, it’s not capitalism. The finest capitalist is Scott McNealy, a capitalist so pure that when he was being devoured by Oracle he believed that it was his duty to capitalism to die, and I admire that. There is no purer a capitalist than Scott McNealy. And read McNealy’s final email to Sun employees, and it’s almost prescient, McNealy says: “You know what, in 30 years I never had to hide the newspaper from my children.” An achievement that Uber violated on like month two? Where are Travis’ parents? Are you not humiliated? How did you raise him to be so divorced from what really, actually, truly matters? What the living [expletive] is wrong with us? Maybe it’s me?

I continue to be impressed by Joyent, and Bryan Cantrill’s engineering principles. It sounds like a great place to do your best work.

Recorded at GOTO 2017 for an Arrested Devops episode: Old Geeks Yell At Cloud

Last week, there was a mailing list post on the clojure-dev mailing list noting that several of the new predicates in Clojure 1.9 alphas return true or nil. The three new predicates are: qualified-keyword?, qualified-ident?, and qualified-symbol?. Previously, all predicate functions in Clojure core, i.e. functions that end in a ? have returned true/false. In this post I want to examine the pros and cons of this new behaviour.

If I’ve missed anything here, please get in contact and I’ll update the post.

Pros to some predicates returning nil

• The main argument for some predicates returning nil is that the predicate still returns a falsy value. Idiomatic Clojure code usually doesn’t need to distinguish between nil and false.
• The docstrings for qualified-keyword? for example says: “Return true if x is a keyword with a namespace”. It doesn’t say anything about what happens if it doesn’t have a namespace, so returning nil or false are both technically valid interpretations.
• Not coercing the output from qualified-keyword? into a boolean is faster. On my computer qualified-keyword? takes roughly 3.5 ns to run, and a version that returns a boolean value takes around 6.5 ns. In absolute terms they are both pretty small though.

The first two points aren’t strong arguments for returning nil, rather they argue that it doesn’t matter whether the functions return nil or false.

Cons to some predicates returning nil:

• The biggest downside to this change is that it breaks a core convention that Clojure and the community has held around predicates, namely that any function ending in ? returns true or false. This is my biggest concern about the changes. You can find this expectation in:
  • Programming Clojure: “A predicate is a function that returns either true or false. In Clojure, it is idiomatic to name predicates with a trailing question mark, for example true?, false?, nil?, and zero?.” - Programming Clojure, 2nd Ed., Page 27.
  • Clojure’s own library coding standards: “Use ‘?’ suffix for predicates. N.B. - predicates return booleans”. That page also has the disclaimer: “Rules are made to be broken. Know the standards, but do not treat them as absolutes.”
  • The community Clojure Style Guide: “The names of predicate methods (methods that return a boolean value) should end in a question mark (e.g., even?).”
  • All of the Clojure standard library functions that end in a ? return a boolean value. Anyone learning Clojure would be justified in assuming that all functions that end in ? return a boolean value if that’s the convention they have always seen.
  • A mailing list thread on predicates in the aforementioned Programming Clojure book.
  • A mailing list thread about this exact question, whether all Clojure functions that end in ? should return a boolean value.
  • Tutorials Point: “Predicates are functions that evaluate a condition and provide a value of either true or false.”
  • StackOverflow on naming rules: “The main function naming conventions seem to be … Use ? to indicate a predicate that returns true or false: sequential?”

• The second biggest problem is that qualified-keyword? can return three values. “How is that?” you might be asking, “Didn’t you just say that the functions return true or nil?”. I thought so too. However as I was looking at the implementation of these functions, I realised that qualified-keyword? can return false as well, if not given a keyword. For example:

  user=> (qualified-keyword? ::abc)
  true
  user=> (qualified-keyword? :abc)
  nil
  user=> (qualified-keyword? 'abc)
  false
  

  It is fairly common to use group-by or juxt with a predicate function to partition a collection into two groups. If you use any of the new qualified* functions, you will end up with three groups. Based on Alex Miller’s tweet, it seems like this was considered and accepted.

• If these predicates are used at the boundaries of systems or in interop with Java, then it would be easy to forget that the qualified* predicates may return nil, and end up passing null into a Java method as a parameter when you meant to pass false. You could also return false under certain input when you expected the function to only return true or nil, or return nil when you were expecting the result to be a boolean. These kinds of bugs can be very subtle, especially with Clojure’s falsy handling.
• ClojureScript code is a lot smaller and enables more optimisations when it can guarantee that a boolean value is returned.
• Clojure gets similar benefits from the JVM when it can mark the function as returning a Boolean.
• Historically, Clojure has made a distinction between functions that return truthy and those that return true. There are predicate functions in core that return a truthy value like some and every-pred, but they don’t end in a ?. This change starts to dissolve that distinction.

Summary

Personally, I don’t see a strong reason to keep the current behaviour of the new qualified predicate functions, but you might see things differently. Whatever the outcome, I’m glad that in Clojure we don’t have to name all of our boolean functions with an “Eh” suffix.

Update

Alex Miller suggested to file a ticket about this behaviour, so I opened CLJ-2141.

Since my post a few days ago on the Uber-Alphabet lawsuit, there have been a few new developments.

Levandowski consulting for Uber

In that post I wrote:

… no funding appears to have been taken from Uber, or any other company (If there turn out to be payments from Uber to Otto prior to the acquisition then that would be Very Bad for Uber).

Not long after, Johana Bhuiyan at Recode posted a story which suggests that Uber CEO Travis Kalanick hired Otto CEO Anthony Levandowski as a consultant for Uber’s self-driving car around February-March 2016. Even after reading the article several times and sleeping on it, I still can’t quite believe it.

Now, sources are adding more to that claim. Kalanick hired Levandowski as a consultant to Uber’s fledgling self-driving effort as early as February 2016, six months before Levandowski publicly got his company off the ground, according to three sources.

If this was a legitimate business arrangement, the timing makes no sense at all. Levandowski had just left Waymo weeks earlier. While it might have been difficult for Alphabet to bring a lawsuit on these grounds, the optics for Levandowski advising Uber are terrible. Additionally, Uber and Otto are competitors in the self-driving vehicle space, and Uber is famously aggressive. That a CEO of one company would be advising one of their direct competitors within months of forming their own self-funded startup is truly strange.

If this wasn’t a legitimate business arrangement, then it also doesn’t make much sense purely because it looks so suspicious, especially in light of Alphabet’s trade secrets lawsuit. It brings the start of Uber’s direct involvement with Otto to within weeks of Otto being formed. If the plan all along was for Otto to join Uber, then it does make some kind of twisted sense for him to be advising the Uber self-driving car team.

A little birdie tells me that we haven’t seen the last on this particular thread of the story.

Naked Capitalism on Uber

Hubert Horan has just published another article in his series on Uber and whether it can ever increase overall economic welfare.

The answer is that Uber is attempting to implement an innovative and disruptive strategy for achieving market control — a strategy radical different from every prior tech oriented startup — but those disruptive innovations have nothing to do with technology or the efficient production of urban car services.

Otto purchased another Lidar company

A reader sent me a link to this article by Reuters discussing an acquisition of Tyto LIDAR. The title is “Uber’s self-driving unit quietly bought firm with tech at heart of Alphabet lawsuit”. The title isn’t accurate, as it was Otto that acquired Tyto (for an undisclosed sum) in May 2016. Uber then acquired Otto/Tyto in August 2016.

Levandowski: “We did not steal any Google IP”

Forbes published an article on 28 February, 2017 which contains part of an interview they did with Levandowski in October 2016.

Q: The question is, Google has been working on this for however many years. You guys (Otto) are a year old or something like that.

A: We started in January. How did we catch up?

We did not steal any Google IP. Just want to make sure, super clear on that. We built everything from scratch and we have all of the logs to make that—just to be super clear.

But this is my fourth autonomy stack. I did the DARPA Grand Challenge.

I wonder if “we have all of the logs” is also going to be Alphabet counsel’s opening argument?

If you’ve been following tech news over the last few weeks, you have probably seen several stories about Uber, all negative (bar this one about flying cars). I suspect that what is coming next will prove to be a far bigger story than all of the other incidents so far.

N.B. all of this article is sourced from filings and allegations that Alphabet has made, as well as reading between the lines. Uber will probably contest these claims in court.

Update: I’ve published some updates on the lawsuit. You can keep track of all the posts related to the Alphabet lawsuit here.

In the last few weeks Alphabet filed a lawsuit against Uber. Alphabet and Waymo (Alphabet’s self-driving car company) allege that Anthony Levandowski, an ex-Waymo manager, stole confidential and proprietary information from Waymo, then used it in his own self-driving truck startup, Otto. Uber acquired Otto in August 2016, so the suit was filed against Uber, not Otto.

This alone is a fairly explosive claim, but the subtext of Alphabet’s filing is an even bigger bombshell. Reading between the lines, (in my opinion) Alphabet is implying that Mr Levandowski arranged with Uber to:

1. Steal LiDAR and other self-driving component designs from Waymo
2. Start Otto as a plausible corporate vehicle for developing the self-driving technology
3. Acquire Otto for $680 million

Below, I’ll present the timeline of events, my interpretation, and some speculation on a possible (bad) outcome for Uber. The timeline references section numbers from Waymo’s amended filing, so you can read the full context yourself. You can also read the original filing.

Timeline of events

The main timeline of important events is as follows:

• Summer 2015 - Anthony Levandowski told Pierre-Yves Droz, a colleague at Waymo, that he had talked with an Uber executive about forming a self-driving car startup and that Uber would be interested in buying that startup. (Droz 28)
• November 17, 2015 - Levandowski registers a domain for 280 Systems, the company that would later become Otto. 280systems.com can be linked to a public email sent February 4, 2016 from someone with a 280systems.com email address looking to do testing of a semi truck with “specialized equipment”. (Filing 41)
• December 3, 2015 - Mr Levandowski searched the Alphabet intranet for instructions on how to access Waymo’s design server on his work laptop. Based on Gary Brown’s deposition (a Google forensic security engineer) this was an SVN server. (Brown 15)
• December 11, 2015 - Anthony Levandowski installed TortoiseSVN and downloaded 9.7 GB of data from the SVN repository. (Brown 17)
• December 14, 2015 - A USB card reader was attached to the laptop for eight hours. Google doesn’t appear to have logged what the laptop did over that time, but the implication is that data was copied from the laptop to a memory card. (Brown 18)
• December 18, 2015 - Levandowski reformatted his work laptop from Windows to Goobuntu (Google’s custom version of Ubuntu). This laptop wasn’t used again after December 21. To be fair, it was only used three times between March and November 2015. Presumably, he was still doing work during this time, just on another computer? (Brown 19, 20)
• January 4, 2016 - Levandowski downloaded five confidential technical Waymo documents from Google Drive to a personal device. (Brown 22)
• January 5, 2016 - Levandowski took a walk with Droz. In Pierre-Yves’ deposition, he claims that Levandowski “told him that he planned to ‘replicate’ Waymo’s technology at a new company he was forming.” (Droz 27)
• January 11, 2016 - Levandowski downloads another file from Google Drive relating to Waymo’s self-driving car development schedule and timeline. (Brown 23)
• January 14, 2016 - Levandowski was seen meeting at Uber’s headquarters and the news travelled back to Droz. Droz asked Levandowski about this, and he admitted he had met with Uber and was looking for investors for his new company. (Droz 29, Filing 48)
• January 15, 2016 - Levandowski officially forms 280 Systems (in stealth mode). Note that this was one day after his meeting with Uber. (Filing 49)
• January 27, 2016 - Levandowski resigns from Waymo without notice. (Filing 49)
• February 1, 2016 - Levandowski forms Otto Trucking (this is also in stealth mode). (Filing 49)
• Spring (March-May) 2016 - “Kalanick began courting Levandowski this spring, broaching the possibility of an acquisition … The two men would leave their offices separately—to avoid being seen by employees, the press, or competitors.” - Bloomberg. Update: I forgot about this article, but was reminded by hammock on Hacker News.

• May 17, 2016 - Otto launches out of stealth mode. As far as I can tell, they never took on any venture funding, instead self-funding (emphasis mine):

  Many of Otto’s founders have done well for themselves over the years, and it shows: the company is entirely self-funded right now without any external investment. (In the wake of the reported $1 billion Cruise Automation sale to General Motors, I ask Ron if the plan is to get acquired, but he’s insistent that they’re focused on bringing a product to market.) Even George Hotz’s scrappy upstart Comma.ai has recently taken on venture funding from Andreessen Horowitz. - The Verge

  In the photo for their announcement I count 35 people. By the time Otto was acquired, they had 91 employees. This seems like a lot of salary commitment to take on via self-funding by Otto’s four co-founders (all ex-Google). On the other hand, depending on the incentive pay they received at Google, they may have had plenty to cover several years of salaries between them.

• August 2016 - Levandowski received his final multi-million dollar payment from Google (presumably a deferred bonus?). (Filing 55)
• August 19, 2016 - Shortly after the final payment was awarded, Uber announced a deal to acquire Otto for $680 million. (Filing 55)
• Summer 2016 - Levandowski’s sudden resignation, Otto’s quick launch, and Uber’s subsequent acquisition of Otto caused Waymo to suspect that their IP had been misused. Waymo investigated this and discovered Levandowski’s actions prior to leaving. (Filing 57)
• December 13, 2016 - A Waymo employee was accidentally copied on an email from one of its LiDAR-component vendors titled OTTO FILES. The email contained a drawing of what appeared to be an Otto circuit board that resembled Waymo’s LiDAR board and shared several unique characteristics with it. (Filing 59)
• December 2016 to February 2017 - Waymo tried to obtain further information on whether Uber was using their LiDAR designs. This is also known as “Getting your ducks in a row”. (Filing 60)
• February 9, 2017 - A Nevada public records request turned up a filing Otto/Uber made that they were using an “in-house custom built 64-laser” LiDAR system. This was enough to confirm to Waymo that they Uber was using a LiDAR system with the same characteristics as Waymo’s. (Filing 61)
• February 23, 2017 - Alphabet makes their first filing against Uber.
• March 10, 2017 - Alphabet amends their filing, and asks for an injunction against Uber’s self-driving car program.

Implications

From Waymo’s filings, it seems that they have Levandowski dead to rights on stealing their LiDAR designs. That alone should be enough to bring Uber’s self-driving car program to a halt and cause some big problems for Levandowski. California’s Trade Secrets law is weaker than other states, but if successful, Waymo will be able to seek an injunction, damages, and attorney’s fees. Because all law is securities law, the SEC may also be able to bring a case against Uber (similarly to their case against Theranos).

I’m guessing, but I think the reason that Alphabet hasn’t directly accused Uber of conspiring with Levandowski is that they don’t have enough evidence. When they get to discovery, they will be looking for it. You would think that no-one would be dumb enough to send emails like that, but you would be wrong.

Several things suggest Otto’s intent to be acquired by Uber:

• Levandowski told Droz in the summer of 2015 that he had talked to an Uber executive about forming a self-driving car company and Uber acquiring them. This is a pretty clear signal!
• Levandowski formed 280 Systems the day after meeting with Uber executives and two weeks before leaving Waymo. He claimed he was talking to them about funding, but no funding appears to have been taken from Uber, or any other company (If there turn out to be payments from Uber to Otto prior to the acquisition then that would be Very Bad for Uber). The timing of Levandowski’s actions suggests certainty about something, and if it wasn’t funding, then what was it?
• According to a Bloomberg article in August 2016, Travis Kalanick and Anthony Levandowski started talking about an acquisition in the Spring of 2016. Spring is usually defined as March-May, which sounds like they may have been talking about an acquisition before Otto had even been publicly unveiled. I’m a bit skeptical about Uber’s statements for this article, given Alphabet’s allegations, but it seems like a weird kind of detail to make up.
• That Otto hadn’t received funding from any VC’s is unusual. With 91 employees, getting paid $150k/year (this might even be too low given they are working on self-driving cars, one of the hottest spaces in tech right now), they would have had a $13.6 million/year burn rate just for salaries. Otto always aimed to get to market quickly, but getting to profitability without funding seems like it would have been very hard, especially on the accelerated timescale they were working towards and the need to likely hire many more people to get to production. All of Otto’s public self-driving car and truck competitors have taken venture funding. However, as someone working on a bootstrapped SaaS application, I’m sympathetic to wanting to self-fund. Update: Counterbalancing this point, it looks like Levandowski had previously sold three startups to Google for nearly $500 million. Those facts are somewhat in dispute, and it’s not clear how much he personally made from the sales. However it does seem plausible that he would have had enough cash to self-fund Otto with his co-founders.
• Otto was acquired only four months after their public launch. While it’s not that unusual for companies to be acquired quickly, it is still very quick, and for a lot of money.
• Uber has considerable internal self-driving car expertise. I’m speculating, but it seems likely that Uber would have found out (or should have found out) during due diligence, that Otto’s LiDAR system could not have been built and developed independently in the six months the company was operating. Updated: Otto purchased Tyto Lidar in 2016, so they may argue that their Lidar system came from Tyto.

There is no smoking gun email (yet), but there is a strong implication that Uber and Otto planned this from the start.

(Possible) Consequences

If this is true and can be proved in court, then it would be a massive blow to Uber. The worst case for Uber would be:

• Uber gets dealt an injunction on their self-driving car project. They have to start again, a long way behind other companies.
• Uber’s name is mud, they struggle to raise more money from investors, especially on good terms. Uber has raised at least $15 billion at a $68 billion valuation.
• Uber is currently losing money at $2-3 billion/year. Uber passengers only pay 41% of the cost of trips, with investor capital making up the difference. Update: I was wrong about Uber passengers only paying 41% of the cost of trips. I can’t find a publicly available number on how the trips are subsidised. Regardless, “Lose a billion here, a billion there, pretty soon, you’re talking real money.” Update 2: See the appendix for more details on this.
• With significant negative margins, no way to become profitable in sight, and a terrible media narrative after the Alphabet lawsuit, sexual harassment, aggressive/illegal behaviour, e.t.c., they cannot IPO.
• Because their self-driving car plans are still so far off, they can’t lower their costs to become revenue neutral.
• I suspect that a large part of Uber’s appeal is their low pricing. If they were to raise prices to cover their driver costs (not even covering the significant costs of their own operations), demand would dry up.
• Without any way to raise more money or reduce their costs, Uber runs out of money and folds.

This is admittedly the very worst case scenario for Uber, and there are lots of places along this downward trajectory that they could pull up from. If it’s proven that Uber intended to acquire Otto while Levandowski was at Google (this might be established more concretely in discovery), then it’s hard to see how Uber’s CEO Travis Kalanick could keep his job. Uber has had a bad month, and it doesn’t look like things are going to be getting better any time soon.

Postscript

This post is made up of a mix of filings from Waymo, reading between the lines, and some speculation. Keep in mind these are all allegations and haven’t been proven in court. Please let me know if I’ve made any mistakes, and I’ll correct them.

I’d encourage you to go over the filings yourself, as they are very readable, and give a lot more context to the story than I was able to here.

Appendix

I originally posted that Uber was only charging 41% of the cost of the trips, based on this article which I misread. The 41% number is the total cost of the trip including driver compensation as well as corporate expenses.

Alyssa Vance sent me the calculations you would make to work out the farebox ratio:

Farebox ratio = fares / total cost of operations Total cost of operations = fares - profits Farebox ratio = fares / (fares - profits)

For 1H2015: Farebox ratio = 3,661 / (3,661 - -987) = 3661 / 4648 = 78.8%.

The State of Clojure 2016 survey results have just been published. Last year I wrote an summary of the free text comment portion of the State of Clojure 2015 Survey. I enjoyed writing it, and it was my second most popular post of the year, so I’m repeating the process again.

In his summary, Justin said that 62% of the responses were positive. That number sounded low to me (but was presumably calculated by SurveyMonkey). I would have estimated closer to 80% after reading through them all. A little under one quarter of the 2420 survey respondents left a comment.

I’m reusing most of the same categories from last year so interested readers can compare with last years post. Some comments have been lightly edited for spelling, clarity, brevity, and niceness.

Error messages

Error messages were the biggest pain point for people last year. This year there were still many complaints about error messages and stack traces, but a lot of people are waiting to see what spec brings. There was a lot of discussion about spec error messages several months ago, but it seems to have gone quiet. I’m really hopeful that spec will improve error messages.

This year Figwheel has started providing very sophisticated reporting of compile errors, and configuration problems. It has made a massive difference to my ClojureScript workflow. Thanks Bruce!

Please Please Please can we get better error messages. …

ClojureScript has come a long way, but I still encounter errors that are totally perplexing. Better debugging would help enormously.

Error messages are very frustrating and it is hard to find where the error occurred and why. Errors coming from underlying Java code are only somehow relevant to the Clojure that produced them. Programming with dynamically typed language rocks when inferred types align with your idea, but when it’s not, things get fuzzy.

Please, please, please, please, improve error messages. This would single handedly improve: new user onboarding, community feedback (let’s admit it - it is a small community), rapid iterations, usage of the REPL, usage of spec and testing, and other areas. …

I consistently see error messages being the biggest barrier for learners of Clojure, and even more so for ClojureScript

I think a concerted focus on improving Clojure’s error reporting & handling would benefit both newcomers to the language and experienced developers alike and would result in considerably less wasted time & effort.

Docs

Last year clojure.org had just been revamped and open sourced. I wrote at the time:

I have high hopes that it will become a central source for high quality, official documentation and ease the pain for newcomers.

clojure.org has had some contributions from the community, but it still doesn’t have the breadth of material needed to be a central source. I would love to see something like Python’s web documentation for Clojure. Renzo Borgatti is writing a mammoth book “The Clojure Standard Library” which will cover the entire Clojure standard library.

… Please improve the documentation. Recently I heard someone describe Clojure documentation as “comically terse”.

A simple way to get someone up and running that is a standard for the community would be great. There is nothing more frustrating than telling new people to “Google” for a solution and pick one you like… They never get further than reading the docs.

Clojure appeared to be a nice language when I started with it and I do not regret this decision. The flip side is that I had hoped that the poor documentation would have gone away by now — 1.4 was the first version I used and it does not seem to have improved. That’s a shame. Documentation helps new users and really, hinders nobody.

Clojure docs are too terse. They assume that the reader already fully understands the concepts being described, and merely needs a refresher. …

Clojure’s community is surprisingly small given it’s output. This leaves documentation and tutorials sparse because they require time and effort that is in short supply. …

I think both clojure.org and clojurescript.org could use a better “Get Started” experience. It’s our best opportunity at a first impression but we rely too heavily on third party docs. For example, on cljs.org the reference section starts with compiler options. Doesn’t really capture the imagination.

Setup/tooling

Again, Figwheel has been leading the way in improving tooling on the ClojureScript side. Tooling is still a pain point, but seems to be less so than in previous years. For Clojure editors, Cider, Cursive, and vim-fireplace are all used pretty much the same amount as last year, but Atom has entered fourth place, presumably coupled with proto-repl.

One thing we’re used to from C#/Java that would be awesome to have is a better unit testing framework with IDE integration. …

The build toolchain for cljs has been a pain. All of my learning has come from cloning public repos and seeing how they do it.

A huge thanks to the community for invaluable tools like Leiningen, Parinfer and the various IDE plugins like ProtoREPL or Cursive. And of course huge thanks to the core team for excellent stewardship of Clojure itself.

While tooling for Clojure is improving there needs to be a lot more resources devoted to it. I am currently in a Java shop and the only realistic option is Cursive.

Startup time

Startup time was another persistent complaints this year. Unfortunately there wasn’t always enough information about whether startup time was a problem in development or production. There are several good options for avoiding constantly restarting Clojure REPLs in development (and in production), but perhaps for newcomers these are too complicated to setup, or they don’t know about them?

Love Clojure … hate its startup time!

Love the language and will keep at it. Primary frustration is with the start up time and tooling. In particular, I’m finding it difficult to quickly test the backend and frontend of my application with Boot.

… We love functional programming, but hate Clojure’s long startup times. We do what we can to minimize this (using test-refresh, REPLs, etc.), but it is still very painful, and we find ourselves twiddling our thumbs waiting for a restart several times a day. Similarly, our Clojurescript compiles take ~60 seconds (:simple optimizations) or ~30 seconds (:none optimizations). This slows us down substantially. Coming from Python, where compile and startup times are sub-second, this is the biggest complaint from our team.

Clojure would be perfect with faster startup time and a little less memory usage. Seriously I don’t even mind the java stack traces.

REPL startup time is all I care about. I use emacs+cider, and it takes an age. Otherwise, I am completely happy with Clojure :)

Marketing/Adoption

Justin specifically mentioned marketing and adoption as a common theme amongst the feedback:

One relatively stronger theme this year was the need for better marketing for the purposes of expanding or introducing Clojure within organizations, which is a great area for contribution from the entire community.

In my opinion, one of the areas where Clojure could improve on marketing is on the main Clojure and ClojureScript websites. I think Scala in particular has done a really good job of this. Elm and Rust also do really well in presenting the main reasons why you would want to use their languages. The community isn’t able to help with this, as contributions to style and templates are not currently wanted.

Last year I mentioned Cognitect’s case studies on Clojure adoption, this year Juxt has done some great work with their case studies of companies using Clojure in Europe.

Anecdotally, I’ve seen fewer people coming along to the Auckland Clojure Meetup than in previous years, although we’re working on a fairly small sample size. I’m not sure what (if anything) to make of that.

I would do 100% of my development in Clojure if the enterprise-y company I worked for allowed it. “Reason for not using Clojure as much as you would like”? Management not on board.

I’d love to see more “serious” support for ClojureScript: when I present ClojureScript to colleagues, it looks like a thing supported by several enthusiasts rather than a platform supported by a company.

Clojure is very solid. As a frontend developer, a stable build system, DCE and syntax stability are very valuable for me. I failed to convince my CTO on Clojure and instead we stuck to ES6/ES7. The main concern of management was hiring and training people. Although the learning curve for Clojure is easy, people still have a perception that LISP syntax is esoteric and difficult to pick up for someone completely new to the ecosystem. This myth has to be busted on a larger scale.

Language is great, community is great, the “marketing” is not that great. You guys have a great language and you are struggling to sell it.

[I] would love to see better marketing from Cognitect and other Clojure centric shops. Selling Clojure to a Java shop is not easy. It can and should be easier. (and simple, but I’ll take “easier” here first)

As an average developer fluent in Java, I would love to use Clojure more, but the biggest hurdle for me is the lack of peers interested in Clojure. At the local meetup people report the same situation at their organisations. Pity, because Clojure is super cool! Thank you.

Love Clojure, really. Can’t convince my peers that it’s worth investing the time to learn it though.

The Clojure community needs a “Rails killer,” and only Arachne holds serious promise for that.

Clojure/ClojureScript ecosystem could benefit from stronger stewardship from Cognitect to propel it into the mainstream with a focus on a killer app or a industry domain similar to the way Light Bend has been focusing on enterprise and reactive system to promote the Scala ecosystem. …

I’m in Shanghai and we barely have full-time Clojure developers in China. We formed online groups, but I guess we need help to push it to the next level.

And the age old developer question:

How can we get management to understand what they don’t understand?

Language Development

Like last year, there are still concerns about the contribution process, and the opaque decision making process for Clojure’s development.

Engagement of community is still sub-optimal, there are talented individuals who could be engaged more and productively so without opening it up to the peanut gallery.

I wish that the core Clojure development process was more flexible and friendly. I (and all the Clojure developers I know) have pretty much given up on trying to make suggestions or tickets about Clojure because I usually wind up banging my head against the wall and getting frustrated. The core team are under no obligations to explain themselves or their motivations, but they would save a lot of frustration from new community members wishing to contribute if there was a prominent document outlining the philosophy, and what kinds of changes and suggestions are and aren’t welcome.

A more open approach to development and contributing to Clojure would be appreciated. I’d love to contribute to Clojure but the mess of a lot of the code in Clojure and the JIRA-based contribution model is a barrier. I know that’s what Rich likes and see the rest of Cognitect are happy contributing in this way but I’d love to see something more open and approachable.

The slow rate at which JIRA issues are addressed remains a frustration, and provides a disincentive for contributing. Features that Cognitect cares about get rushed into the language half-baked, while well-thought out patches from years ago languish.

A little concerned over how ‘arbitrary’ some design decisions seem to be and how inflexible the core team is. Running instrumented post-condition specs is such an obvious idea for example but it has been deemed not necessary “from on high”.

The issue tracker is well tended during the earlier workflow stages. There seems to be a bottleneck later on. I hope 2017 will bring the project’s founders to modes of community contribution that are more efficient of the art and tradecraft of the many.

Community

I would say that Clojure’s community is one of it’s greatest assets. There were mostly positive comments for the community, though still some concerns. The Clojurians Slack has been a great resource for a lot of newcomers, and spawned many channels for libraries and topics. IRC is still around, but seems to be less popular, and doesn’t have the breadth of topics that Clojurians does.

Alex Miller is doing a great job addressing the community.

CLJS has come a long way!! to the point we can use it for production development! this community is great! Justin_Smith stands out as ridiculously helpful on IRC … if the world (this community) had more folks like him, it’ll elevate all of our games!

The thing that makes me wary of continuing to invest in Clojure professionally is how few paid opportunities there are for women and people of color. I don’t know what the exact problem is - they are left of networks, don’t have an opportunity to build their skills, or just straight-up sexism and racism - but it is definitely a problem. The current state of things means I will likely not be able to be on teams with women or people of color, and that is a big turn-off for me.

Clojure has the best community after PostgreSQL, in my opinion. I came for the language but I stayed for the community.

Be more inviting to new-comers.. so they stop learning Ruby.

Libraries

A “Rails for Clojure” was a common request so people can start delivering value quickly. Arachne was commonly raised as one possibility to provide this.

Clojure/ClojureScript it’s very cool, but not very practical nor efficient in many typical business case scenarios. I’m missing a full stack framework like Grails or Ruby on Rails or Django: there’s nothing like that for the Clojure world: it’s not about a project template but about the quick prototyping (with the customer by your side) these frameworks allow.

… There is also no good Clojure Web Development story: Pedestal looks interesting, but not actively developed and unsupported, Arachne is years away from being complete and useful, Luminus/Duct are initial scaffold project generators. It’s hard to delivering some value quickly - user have to dig through all underlying libs and how they work together.

… Clojure web development needs a “Rails” to overcome the chicken-and-egg problem of getting enough developers to be able to hire for it. …

I hope to write a lot more Clojure. No, I hope to do a lot more with less Clojure. And looking forward to using Arachne.

Other targets

Many people are looking to run Clojure on alternative platforms or reduce host dependence. LLVM was a common request. Some are looking to move away from the JVM, while others are looking to move into environments that Java and JavaScript aren’t suited for. This is an interesting request, though one of Clojure’s original goals (and still on the Clojure homepage) is to be a hosted language. I’m not sure whether it’s possible for these two desires to ever meet? Graal and Truffle are also interesting possibilities.

The biggest thing I’ve noticed for beginners on forums / blog comments is they are afraid of the JVM. …

I’ll never rewrite all my Scala into Clojure unless some sort of Cognitect Clojure OFFICIAL LLVM effort is made. Scala Native is [beating] Clojure.

Clojure’s hosted nature is its biggest downfall, in my opinion. As a systems programmer looking to lisp + immutability for saner concurrency, the cost of Clojure’s startup time and memory usage is very high. …

The one thing that I think would drive Clojure to a new level of adoption across the industry would be for someone to do an actual LLVM implementation of Clojure. Not a “close variant” of Clojure, but real Clojure. This would probably yield some performance boost beyond Java, but more importantly it would open up Clojure to environments that are simply not amenable to Java (or Javascript) for whatever reason. Some people have moved in this direction, but either have not completed the work, or have implemented their own “variants” of Clojure. What I wish someone would do is implement something with LLVM that is at least as close to Clojure as Clojurescript is.

I really think an opportunity is being missed by dismissing the c++ ecosystem, and I think that something that should be given somewhat serious consideration to by somebody would be to leverage LLVM with JIT and get a clojurescript running in that setting. There are significant legacy environments to be liberated there.

I would love for there to be some sort of compile-to-bundle with Clojure such that you have a single artifact that doesn’t require an external JVM installation. Like Go programs. An embedded JVM (perhaps).

Typing

As we’ve all learned this year, people are worried about types. Spec is the biggest movement in this direction, and the number of type related comments has dropped a lot since last year.

I know that Spec should help a lot with the error messages once we move to 1.9, although people coming from a non-Java background still have a lot of learning to do.

It is just sad that people who love Clojure (Colin Fleming, Steve Yegge, Adam Bard), have to use Kotlin sometimes instead (better startup times, static typing and Java interop like fast multidimensional arrays)

I hope Spec will find its way into tooling, especially Cursive.

Looking forward to learn and use spec

I’d most like to see improvements to the Clojure compiler. Error messages, performance, better Java interop and simple static type checking seem most important.

Compliments

As I mentioned at the start, the overwhelming majority of comments had positive things to say about Clojure. Alex Miller also deserves a special mention for his work with the community, and maintaining the Clojure infrastructure.

I sincerely thank Clojure(Script) community to make LISP revolution back to live stage and making us realize the importance of focusing on core things which matter

I have been programming since 1979. Clojure is a work of art.

The community has been unbelievably great and I hope it stays true to its roots! Keep up the good work and I can’t wait to see where Clojure/Script goes next!

The community is amazing, with a special shoutout to Alex Miller for being such a great part of it.

Happy Clojure user for over 4 years. Still loving every minute :-).

Finally, I found a comment that I think sums up the general feeling of the community (and my own):

No one and nothing is perfect, but I (for one) am very appreciative of the work that has been done and is on-going around Clojure/ClojureScript and the community in general. People tend to ‘harp’ on the things that aren’t just right (in their opinion) and forget about all the things that are amazing. I just want to say thanks, and keep up the superb work! :-)

I think the future of Clojure is bright.

Shockwaves rang out through the Clojuresphere today with the news that Datomic is changing their licensing to drop the per-process limits. This is big news if you were limited in the number of processes you wanted to run.

The major changes in a nutshell:

• There are now no limits on process count
• Datomic Starter is now limited to one year of updates, then you need to pay $5,000 for Datomic Pro, or stay on the current version when your license expired.
• Datomic Starter can now run the Memcached cache.
• All Datomic Pro licenses are now $5,000, and annual maintenance is also $5,000/year.

If I’ve got any of the following wrong, please get in touch via email and I’ll update my post.

The old pricing model

Datomic launched in March 2012 with a paid option and in July 2012 added Datomic Free. In November 2013, Cognitect launched Datomic Pro Starter Edition. The old pricing page is on archive.org here. This model was easy to understand, as it mapped well to existing database licensing patterns of ‘perpetually free with limitations’ or ‘paid without limitations on a per node basis’.

Datomic Free

• Free (as the name indicates)
• Limited to storing data in memory on the transactor, or on the transactor’s disk.
• Freely redistributable (i.e. in on-premise or open source software)
• Only able to run two peers (clients) and a single transactor. If the single transactor fails, then you won’t be able to write to the database until another one starts.
• Community support

Datomic Pro Starter Edition

• Free
• Support for all storage backends (SQL, DynamoDB, Cassandra, Riak, Couchbase, Infinispan)
• Limited to 2 peers and a single transactor
• Not redistributable
• Community support
• Limited to 1 year of maintenance and software updates, though you were able to renew your Datomic Pro Starter Edition license each year for free (more on this later).
• When your updates expire, you can continue using that version of Datomic, but you won’t be able to use any future versions.

Datomic Pro

• Paid
• Support for all storage backends
• Able to run a second transactor in HA standby to take over if the first one fails or for rolling updates.
• Ability to use Memcache to cache segments rather than all peers needing to talk directly to the storage backend.
• Support is included while maintenance is current.
• Pricing scaled linearly from $3,000 for five processes (this includes peers and transactors) up to 30 processes for $16,000. You could upgrade later to higher tiers for the price difference between the old license and the new license.
• Annual maintenance for support and updates was half of the upfront license price
• If an organisation had special needs (more processes, custom EULA, 24x7 support, redistributing Datomic e.t.c.) then you could talk to Cognitect to negotiate terms.

The new model

All versions of Datomic apart from Free now support unlimited peers, high availability, Memcached support, and all storages (more on storage later). This is a significant change, as you can now use Datomic in an almost unlimited fashion for free. There is also a new Client API which is suitable for smaller, short-lived processes, like microservices and serverless computing. The changes are smart, as it frees users up from having to architect their systems around their Datomic license limitations. The new pricing model rearranges the tiers. There is now Datomic Free (unchanged), Datomic Starter, Datomic Pro, and Datomic Enterprise.

Datomic Starter

• Similar intent to the previous Datomic Pro Starter
• Free
• Maintenance and updates limited to 1 year. However, based on discussion on Hacker News, it seems that you can no longer renew your Datomic Starter license. This means that you will need to pay for Datomic Pro to get updates after one year. You can still use whichever version was available when your updates expire. Discussion in the #datomic Slack channel on clojurians matches up with this too.
• Update: Alex Miller said that you can sign up for multiple Datomic Starter licenses for different systems you’re running.

Datomic Pro

• Similar intent to the previous Datomic Pro
• $5,000/year per system including maintenance and updates. For organisations using 16 processes or less, then maintenance will be more expensive (previously $1,500 - $4,500 depending on process count).
• 2 Day Business-Hours-Only Support. The former Datomic Pro didn’t have a published SLA for support, but I suspect that this is just formalising what was previously there.

Datomic Enterprise

• Enterprise integration support (professional services)
• Negotiated license terms
• 24x7 Support
• While this is a new tier in the pricing grid, these options were available as a “Contact Us” note on the former Datomic Pro.

Other changes

Datomic has a snazzy new documentation site. It also looks like as part of the licensing changes, Riak, Couchbase, and Infinispan are now considered legacy storage and are only available to be used under an enterprise license. Standard editions of Datomic only support SQL, DynamodDB, and Cassandra. This change hasn’t been mentioned on the Datomic mailing list or release notes, but probably will be soon.

Datomic has also deprecated the REST API in favour of the new Client API.

There is a new customer feedback portal where you can suggest features.

Summary

If you are a Datomic Pro user then your maintenance is probably going to be higher, although in absolute terms it’s still not a lot compared to developer salaries. If you were on Datomic Pro Starter and want to stay current, then you are now looking at moving Datomic Free, or paying $5,000/year for Datomic Pro. If you were using Riak, Couchbase, or Infinispan then it seems like you’ll need to get Datomic Enterprise.

Datomic from the beginning has always felt like a database that understood the Cloud, and the zeitgeist of computing. It supported AWS DynamoDB and CloudFormation from early on, and their architecture has always felt well suited to cloud systems. The license changes to accommodate the trend towards microservices and serverless computing are a continuation of that.

Before we get started, I want to be clear. I don’t support tobacco, cluster bomb manufacturers, nuclear weapons manufacturers, and the other socially harmful businesses mentioned in the recent brouhaha about Kiwisaver investments into the aforementioned companies. However, I think the reporting that NZ Herald did on this was misleading, in search of a good story at the expense of accuracy.

To recap: the Herald has recently been reporting on Kiwisaver, the NZ government retirement savings scheme (like an IRA). Their big headline was that $150mm has been invested by the major Kiwisaver providers into companies that produce cluster bombs, landmines, and other socially harmful products, and that they may be breaking a law banning investments into cluster bomb manufacturers. When you look into the details, their bold claims don’t look so strong.

Here are a few points that should have been included in the reporting:

• The biggest problem is that the Herald doesn’t distinguish between active management (where fund managers or algorithms chose particular businesses to invest in), and passive management that tracks an index (say agriculture, energy, or the USA stock market). If some of these funds were directly invested in these companies, and banks really were breaking the law, that would be a real story. It’s not clear to me from the reporting whether there was any direct investment into the companies, or investment into clusterbomb index funds, or whether the funds were invested in broad indexes. You can make an argument for both being bad, but active investment in these companies is very different from passively investing in an index fund of the total stock market. The Herald implies that these companies deliberately or knowingly invested in the companies, but I couldn’t see this from the data they provided.
• The total amount invested in Kiwisaver is $32.5 billion, and the amount invested in socially harmful businesses is $150 million. This works out to around 0.46% of the total funds invested. This is not nothing, but it is a tiny fraction of the total assets invested.
• Kiwisaver funds that aren’t investing in these companies are likely doing so through active management of stocks. In general, this will result in higher fees, and depending on who you ask, lower performance (especially once fees are taken into account).
• The charts that NZ Herald produced all give absolute numbers for how much is invested in socially harmful companies, without giving the percentage invested. Westpac, ANZ, and ASB all feature high on the list of investing into these harmful companies, but there is no context given for what percentage of the investments each have made. Westpac has 0.76% in socially harmful businesses. ANZ has 1.27%, and ASB has 0.13% ¹. Without more details on total amount invested in stocks (active and passive) by each fund, it’s hard to tell where and why the differences here come from.
• The amount invested in the socially harmful parts of Northrop Grumman² and General Dynamics ³ are very small, compared to their overall businesses.

Data journalism can be used to illuminate complex topics and explain them for a wide audience. It seems in this reporting that the story came first, and the numbers were presented in a misleading way to back it up. There is a nuanced discussion that could have been had about the ethics of index funds, and socially responsible investing, but that wasn’t what we got here.

N.B.: I may have read the article wrong, and all of the figures provided were active investments (it’s not clear at all to me which is being included). If that’s the case my conclusion would be quite different.

Update: More discussion index/active investments may be coming later this week.

Every week in The REPL I have a section called: “People are worried about Types”. This is based on a section that Matt Levine (my favourite columnist) includes in his daily column “People are worried about bond market liquidity”, and the related “People are worried about unicorns”, and “People are worried about stock buybacks”.

The title is a joke (as is his), I don’t really think there are people worried about types, but it is interesting to see a small but steady flow of type or type related (schema, spec, e.t.c.) articles relating to Clojure each week.

I’ve started a weekly newsletter about Clojure and ClojureScript. Each week will have a curated selection of links (both recent, and older) and a sentence or two about why I think they’re worth reading. You can sign up at therepl.net.

One of the datatypes Clojure gives you is the Record. It is used in both Clojure and ClojureScript, but due to implementation differences, the syntax to use records from one namespace in another is different.

Clojure

Clojure generates a Java class for every defrecord that you create. You need to :import them, just like you would a standard Java class. Lets say we have a small music store app that sells vinyl:

(ns myapp.cool-music)

(defrecord Vinyl [speed])

;;; meanwhile ...

(ns myapp.music-store
  (:import [myapp.cool_music Vinyl]))

(instance? Vinyl v)

;; or

(ns myapp.music-store
  (:import [myapp.cool_music.Vinyl]))

(instance? myapp.cool_music.Vinyl v)

There’s a few things to note here:

1. Because Clojure is generating Java classes, they follow the naming conventions of Java classes, where dashes get converted to underscores.
2. You should probably prefer the first example where the record is aliased, over the second one where the record is fully qualified.

3. Clojure dynamically generates the class for the record when that namespace is required (ignoring AOT compiling). If your code never requires the namespace that the record lives in, then it won’t be created. This will cause ClassNotFoundException errors when you try to import the class. In our trivial example, that would mean changing the ns import to:

   (ns myapp.music-store
     (:require [myapp.cool-music]
     (:import [myapp.cool_music Vinyl]))
   

ClojureScript

ClojureScript generates the code for a record in the namespace it is defined in. You can require, refer, and alias a record just like you would any other function in a ClojureScript namespace.

(ns myapp.cool-music)

(defrecord Vinyl [speed])

;;; meanwhile ...

(ns myapp.music-store
  (:require [myapp.cool-music :refer [Vinyl]))

(instance? Vinyl v)

;; or

(ns myapp.music-store
  (:require [myapp.cool-music :as m))

(instance? m/Vinyl v)

;; or

(ns myapp.music-store
  (:require [myapp.cool-music))

(instance? myapp.cool-music/Vinyl v)

There are no hidden gotchas with requiring records in ClojureScript. At one point ClojureScript supported importing records like Clojure, but this was backed out later.

Clojure and ClojureScript

If you want to work with Clojure and ClojureScript (and let’s face it, who doesn’t?) then you can use Reader Conditionals to require a record in both language variants at the same time.

(ns myapp.music-store
  (:require #?(:clj [myapp.cool-music]
               :cljs [myapp.cool-music :refer [Vinyl]]))
  #?(:clj
     (:import [myapp.cool_music Vinyl])))

(instance? Vinyl v)

Most of the time I don’t have any issues with git’s .gitignore system but occasionally it doesn’t behave as I expect. Usually, I add and remove lines until I get the result I’m after and leave feeling vaguely unsatisfied with myself. I always had a nagging feeling that there must be a smarter way to do this, but I was never able to find it. Until today!

Enter git check-ignore. You pass it files on the command line, and it tells you if they’re ignored or not, and why. Sounds pretty perfect right? I won’t give you a run down of all the options, as the man page is surprisingly readable (especially for a git man page!). However the 30-second version is git check-ignore --verbose --non-matching <filepath to check>:

$ echo "b" > .gitignore
$ # a is a file that would not be ignored
$ git check-ignore --verbose --non-matching a
::    a
$ # b is a file that would be ignored (matched)
$ git check-ignore --verbose --non-matching b
.gitignore:1:b    b

--verbose prints the explanation of why a file was ignored. --non-matching prints the file name out, even if Git would not ignore it. If a file is going to be ignored, check-ignore prints out the path to the gitignore file and line that matched. Interestingly, the files don’t even need to exist, git just checks what it would do if they did exist.

Using check-ignore I was able to solve my problem faster, and learn a bit more about git’s arcane exclusion rules. Another handy tool to add to my unix utility belt.

I’ve recently been working on a new ClojureScript application as part of a contract, and I was digging around for things to polish before launch. The app was mostly fast, but I noticed that when the main list of content got to around 40 items, it was a little bit slow to render. I also noticed that it seemed like it got almost twice as slow when I added another 10 items. At this point, you might already be having alarm bells go off in your head suggesting what the problem was likely to be. I didn’t, so I dived into the code to look at the part of the app rendering the main list.

I looked over the code path that rendered the list, and wrapped time around a few suspect pieces of code. After a few checks, I found that a sort-by function in the view was the slow part, though it wasn’t immediately clear why sorting a list of 40 items would take a second. We were using sort-by to order items by state, then reverse date order (newest items first).

sort-by takes a custom sort key function. Our key function was doing some date parsing to parse a string into a date, then subtracting the current unix time from the parsed unix time to give an integer value. The lowest numbers are the most recent dates. I suspected that the date parsing could be the problem, but I wasn’t really sure. As an experiment, I disabled all of the date parsing, and returned the string directly. My sorting was the wrong way around, but it went from taking 1000 ms to 10 ms, a factor of 100x speedup!

A standard sort of the dates (which were in ISO 8601 order, e.g. 2016-04-02T08:24:31+00:00) sorted the oldest dates as the first ones in the list. After a few minutes thinking, I remembered I had recently read the clojure.org guide on comparators. In it, it discusses a reverse comparator:

(fn [a b] (compare b a))

This comparator is exactly the same as a normal comparator, but it will return the opposite result to what the normal one would. Passing this comparator to sort-by kept the 100x speedup, but sorted in the correct order. The list rendered in 10-15 ms, and was now plenty fast enough.

One question remained though, why was the list getting so much slower to render as I added a few more items to it? Of course reading this now, you Dear Reader are probably thinking to yourself, “aha! ClojureScript’s sorting algorithm will be O(n log(n)), and the slow key function will therefore be called O(n log(n)) times.” It took me a bit more thinking than you (I didn’t have a blog post explaining why my code was slow to work from), but I got to this conclusion in the end too.

I really enjoyed this debugging session, as it is not very often that I can both speed up real world code by 100x, and get exposed directly to algorithmic complexity issues. A++, would debug again.

I’m excited to announce I’m starting a new podcast Decompress, hosted by myself and my long time friend Nathan Tiddy. Decompress is a technology podcast, with a New Zealand perspective. We also talk about the wider world of things that touch technology, and how it relates to our lives.

If you like technology, and podcasts, then you may like this too. You can subscribe through iTunes, or in your podcast client of choice, by searching for “Decompress”.

Plumatic (nee Prismatic) Schema is a great tool for adding structural typing to your code.

Specifying standard Clojure types is fairly straightforward, but I recently needed to specify that a value was a goog.date.UtcDateTime. I did a bit of searching on Google, didn’t find anything. I then looked in the company codebase and found it. Here’s a minimal example:

(ns myns
  (:require [goog.date.UtcDateTime]))

(def Date js/goog.date.UtcDateTime)