Dutch Clojure Days 2018

About DCD18

The Annual International Gathering of Clojure Enthusiasts and Practitioners in the Netherlands!


Dutch Clojure Days happened on

Saturday, April 21st 2018, 8:30 AM – 5:30 PM CET.


DCD is a free event that is made possible thanks to our amazing sponsors and volunteers.

Platinum sponsors

Regular Sponsors


Alexander Yakushev

Embrace the JVM

JVM is the native platform for Clojure, yet a lot of its tools and tricks are unfamiliar to Clojure programmers. This talk will bring them to light and show you how the JVM facilities can make your Clojure work even more productive.
About the speaker: Alexander is a software engineer at Grammarly where he blurs the line between programming and natural languages. After being bitten by a radioactive spider with a lambda on its back, Alexander promised to use the obtained Lisp superpowers for good only. In his free time, he contributes to Clojure tooling like CIDER, studies distributed systems, and fills his half-full stack.

Simon Belak

Online statistical analysis using transducers and sketch algorithms

Online statistical analysis using transducers and sketch algorithms. Don’t know what either is? You are going to learn something very cool (and perspective-changing) then. Know them, but want an experience report? Got you covered, fam.
About the speaker: Built my first computer out of Lego bricks and learned to program soon after. Emergence, networks, modes of thought, limits of language and expression are what makes me smile (and stay up at night). The combination of lisp and machine learning put me on the path of always striving to make myself redundant if not outright obsolete. Currently working hard to become obsolete at Metabase where I am trying to build an artificial data scientist and imbue visualisations with understanding and context.

Srihari Sriraman

Practical Generative Testing Patterns

Generative tests are great! But we don’t write them often enough. Why not? As unit tests, they can be harder to write and read. As stateful acceptance tests, they can be brittle, slow, and unjustifiable. I’ll discuss some important patterns to leverage generative tests to their potential.
About the speaker: Srihari is a FOSS enthusiast. He has contributed to Gimp, Eclipse, Diaspora and is excited about opportunities to give back. He has been writing Clojure for over 5 years now, and over this time, he has engineered low latency systems, large analytics platforms, monitoring solutions, distributed payment platforms and multiple simulation testing systems. He is passionate about fostering the Clojure community, conducts workshops, and organizes IN/Clojure. He also works on computational music synthesis and generation as a hobby. He is a partner at nilenso, a hippie tree hugging bicycle riding software cooperative based in Bangalore.

Wilker Lúcio

Implementing Graph API's with Clojure

REST is taking a rest. Over the past years we are seeing a huge growth of graph API’s with GraphQL leading the way. In this talk I will describe what graph APIs can look like on the Clojure side, and even show you how to achieve the best of both worlds by integrating GraphQL with Clojure graphs!
About the speaker: I’m a passionate developer working and learning programming skills since 12 years old, love the way of web development and always researching new technologies. I started real web programming with PHP, but ever trying to learn more and more (passing through Java, Python, C#, ActionScript, Javascript…), currently passionate about Clojure and it’s ecosystem. In recent years I’ve been engaged in the Clojure community, collaborating in projects like Om.next/Fulcro, Devcards, and writing libraries like Pathom. If you’d like to learn more about my work, please check my Github profile at https://github.com/wilkerlucio.

Valentin Waeselynck

lightning talkEasier REPL-based debugging with scope-capture

Tired of manually re-creating Ring requests, app states and database connections simply to evaluate this tiny expression at the REPL? Scope-capture to the rescue, a new Clojure(Script) library that lets you instantly save and restore local bindings at the REPL.
About the speaker: Valentin Waeselynck is the CTO of BandSquare, a platform providing web and CRM tools for managing audiences, built on top of Clojure and Datomic. He authored a few open-source libraries for Clojure and Datomic, including Datomock, scope-capture and Datofu. On the side, he enjoys doing maths and climbing mountains.

Dr Roland Kay

lightning talkStay agile with clojure.spec

You love the sense of liberation and control that Clojurescript gives you and you want the same for your data. A schema for your in-memory data will enable you to change it quickly with confidence. So, the next time that your product manager drops a last minute change request, it will be no stress.
About the speaker: Dr Kay has over ten years experience working in investment banking in London developing financial models and delivering tools which depend on them to trading desks. He came of age with asm, C and C++ and has been using dynamically typed languages to put the power of the core analytics written in C++ in the hands of practitioners who lack extensive software development experience. He has recently discovered the power of functional programming to tame the complexity of front-end development. He is impressed by the ability of clojure.spec to exceed the level of confidence in code integrity that comes with statically-typed languages while retaining the flexibility and fast-prototyping offered by dynamic languages.

Thomas van der Veen

lightning talkWriting an asynchronous MQTT broker in Clojure (and a bit of Java)

A talk about the attempt to write a MQTT broker with Clojure and some Java and make the whole thing non-blocking where possible so that it can scale really well… hopefully.
About the speaker: Thomas has been writing bits of Clojure since 2011 and in 2016 he gave a talk at the Dutch Clojure Days about using MQTT in a Clojure(Script) application. This time he is back with an MQTT broker written in Clojure and just for good measure he he snug in some Java as well… because you can.

Ray McDermott

lightning talkREPtiLe - exercise your lizard brain and share REPLs in a cold-blooded browser

Use REPtiLe to have your own REPL on the web and also see what your team are doing in their REPLs. REPtiLe is ideal for a small number of developers to work together in real-time.
About the speaker: Clojure developer / architect. co-host defn podcast and the apropos youtube channel

Josh Glover

No EC2 instances were harmed during this deployment

Serverless systems promise a bright future of increased battery life for on-call developers’ phones, but do they deliver? This is a story of how we built a backend with Clojure, API Gateway, Lambda, and DynamoDB. Takeaway: when, where, or if this approach fits your problems.
About the speaker: Josh Glover has come a long way since declaring Lisp a completely pointless language in university. 15 years and three countries later, he shudders at the very thought of using a language other than Clojure. He is really interested in teaching programming and increasing diversity in the industry. He currently lives in Stockholm and works for Klarna Bank AB, the leading payments company in the Nordics.

Phillip Mates

How we test at Nubank

Nubank has been shipping business-critical Clojure services for 5+ years. To do so reliably we’ve adopted various approaches to testing, combining unit, integration, & end-to-end tests. This talk will explore our experiences: what’s worked, what hasn’t, and where we are going next with testing
About the speaker: Coming from a background in theoretical programming language research I’ve been coding Clojure at Nubank for over a year. In this time I’ve become the maintainer of Midje, co-authored a library for validating nested data-structures that produces readable diffs (matcher-combinators), and participated in projects to scale Nubank’s testing infrastructure past 100 microservices. Last Fall I moved to Berlin to help Nubank open its first office outside of Brazil. In Berlin, my colleagues and I are focused on building data infrastructure for São Paulo-based analysts and engineers to use.

Pierre-Yves Ritschard

5 years of Clojure: building better infrastructure with parentheses

This talk gives an overview of the initial architectural decisions at Exoscale, an Infrastructure as a Service company where Clojure is in heavy use.
About the speaker: Pierre-Yves is CTO at exoscale where he is responsible for architecture and strategic technology choices, relying on experience in the architecture of very large corporate systems as well as technical product design in several startups. Pierre-Yves is an active member of the open-source community as author of pithos and cyanite as well as key contributions to OpenBSD, collectd and riemann amongst others.

Ray McDermott

lightning talkextemporay - REPL driven comedy

Learn how to compose a library of simple functions and data to deliver the most elegant forms of comedy on the Clojuresphere. You will see how you can get feedback from something better than actual humans: the REPL
About the speaker: Clojure enthusiast: software architect by day, co-orgniser Belgian Clojure User group and co-host of defn podcast by night (some nights anyway).

Code of Conduct

All attendees, speakers, sponsors and volunteers at our conference are required to agree with the following code of conduct. Organisers will enforce this code throughout the event. We expect cooperation from all participants to help ensure a safe environment for everybody.

Need Help?

You can always reach out to us at events@clojuredays.org or on twitter.

The Quick Version

Our conference is dedicated to providing a harassment-free conference experience for everyone, regardless of gender, gender identity and expression, age, sexual orientation, disability, physical appearance, body size, race, ethnicity, religion (or lack thereof), or technology choices. We do not tolerate harassment of conference participants in any form. Sexual language and imagery is not appropriate for any conference venue, including talks, workshops, parties, Twitter and other online media. Conference participants violating these rules may be sanctioned or expelled from the conference without a refund at the discretion of the conference organisers.

The Less Quick Version

Harassment includes offensive verbal comments related to gender, gender identity and expression, age, sexual orientation, disability, physical appearance, body size, race, ethnicity, religion, technology choices, sexual images in public spaces, deliberate intimidation, stalking, following, harassing photography or recording, sustained disruption of talks or other events, inappropriate physical contact, and unwelcome sexual attention.

Participants asked to stop any harassing behavior are expected to comply immediately.

Sponsors are also subject to the anti-harassment policy. In particular, sponsors should not use sexualised images, activities, or other material. Booth staff (including volunteers) should not use sexualised clothing/uniforms/costumes, or otherwise create a sexualised environment.

If a participant engages in harassing behavior, the conference organisers may take any action they deem appropriate, including warning the offender or expulsion from the conference with no refund.

If you are being harassed, notice that someone else is being harassed, or have any other concerns, please contact a member of conference staff immediately. Conference staff can be identified as they'll be wearing branded clothing and/or badges.

Conference staff will be happy to help participants contact hotel/venue security or local law enforcement, provide escorts, or otherwise assist those experiencing harassment to feel safe for the duration of the conference. We value your attendance.

We expect participants to follow these rules at conference and workshop venues and conference-related social events.


Dutch Clojure Days took place at the wonderful TQ, in the heart of Amsterdam (Singel 542, 1017 AZ Amsterdam).