Visit to Clojure Exchange

I have just visited Clojure Exchange. Since it had only one track, there is no point in listing which talks I have attended, since this can easily be seen on the web page of the conference.

It was interesting and there were many great talks and I also met great people among the other participants.

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Devoxx 2016 Visit

As already written in Devoxx 2016 I visited Devoxx in Antwerp 2016.

Hot topics where Java 9 and the functional features of Java 8. But there was a wide range of talks. As in previous years visitors can watch all the talks that they missed or found interesting enough to re-watch online afterwards. In earlier years it was done with „Parlays“ and only available to visitors or to those who pay for it, while it is now available on youtube for everybody. Since the conference has been sold out long before it started, this does not seam to stop people from buying tickets for the conference.

So here is what I did.



Find Links here….

I guess that’s it for today… I hope to visit Antwerp for Devoxx next year again.

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Devoxx 2016

I am going to the Devoxx in Antwerp 2016.
Updates about what I did will follow soon.

As a starter here is my Devoxx-Talk. Let this be the main content for this posting, which is mostly video instead of text. Here is the github repo with the code examples.

Other Links:

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Scala Days 2016

I have visited Scala Days in Berlin 2016-06-15 to 2016-06-17. A little remark on the format might be of interest. The conference is scheduled for 3 days. On the first day, there is only one speech, the first keynote, some time in the late afternoon. During Scala Days 2015 the rest of the day was put into use by organizing a Scala training session, where volunteers could teach Scala to other volunteers who wanted to learn it. But I think two or three sessions on the first day would be better and would still allow starting in the late afternoon with the first keynote. The venue and off course Berlin were great and I enjoyed the whole event.

The talks that I visited were:

Wednesday 2016-06-15

  • First keynote: Scala’s Road Ahead by Martin Odersky about the future of Scala. Very interesting ideas for future versions that are currently explored in dotty.

Thursday 2016-06-16

Friday 2016-06-17


The whole event was great, I got a lot of inspiration and met great people. Looking forward to the next event.

I might write more on some topics, where I consider it interesting, but for the moment this summary should be sufficient.


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ScalaX 2015

It was possible to arrange a visit of Scala Exchange 2015 in London, short #ScalaX.

I visited the following events:

Devoxx 2015

This year I have had the pleasure to visit the Devoxx-Conference in Antwerp in Belgium.

I have visited the following talks:

There is a lot to write about this and I will get back to specific interesting topics in the future…

My previous visits in 2012, 2013 (part 1), 2013 (part 2), and 2014 have their own blog articles.

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ScalaX 2014


I have been visiting the conference Scala eXchange ( #scalaX ) organized by Skillsmatter in London.

Here is some information about the talks that I have attended and the highlights:

The Binary Compatibility Challenge

Martin Odersky

Examples can be constructed for each of the four combinations of binary and source code compatibility.
We wish more of both. The talk is mostly about binary compatibility.
For Scala the conflict is innovation vs compatibility. Java chose one extreme to retain compatibility at any cost, which is considered more like a constraint then a restriction by the Java developers. It is easier for them because they control the JVM which is again close to the Java language. Clojure, Ruby, JRuby, Perl, Python, PHP and some others have less problems with this issue because the software is distributed as source code and compiled when run, just in time.
Reproducible builds are hard to achieve in Scala, just think of the many build tools like ivy, gradle, maven, sbt, ant, make (yes, I have seen it),…
The idea is to split the around 30 steps of compilation of scala into two groups. The first group could yield an intermediate format after around 10 internal compilation steps, which might be stored as tree of the program in a clever binary format. This could be a good compromise and address some of the issues, if kept stable. More likely will programs be combinable compatibly with this format than with binary or source only. It would also save time during compilation, which is a desirable improvement for scala.

REST on Akka: Connect to the world

Mathias Doenitz

Akka-http is the spray 2.0 or successor of spray. It follows the lines of spray, but improves on some of the shortcomings.
It should be used for reactive streams in Akka and is important enough to be part of core Akka.
TCP-flow-control can be used to implement „back pressure“.

Bootstrapping the Scala.js Ecosystem

Haoyi Li

Scala shall be compiled to as second alternative instead of JVM. The target is the browser, not so much server side JavaScript, where the JVM is available and better.
Advantage for applications: Some code can be used on both sides, for example HTML-tag-generation, validation etc. This is more elegant than using two languages. Also Scala might be considered a more sane language for the browser than JavaScript, although JavaScript is not such a bad language, but suffers like PHP and VBA from being used by non-developers who come from web design side and try a little JavaScript as part of their work, tripping into each of the pitfalls that we developers have already had some time ago when we had our first experience.
Libraries prove to be hard. They are huge and it is hard to transfer them. Optimization is needed to deal with this, like for Android development.
Reflection is not available on scala.js. Many things do not work because of that, but enough things to make it useful do work.
Serialization is another challenge, because many frameworks rely on reflection, but there seems to be a solution for that.
Integer types are a little bit crappy. JS only has double which can do 53 bit integers. Long has to be built from two doubles.

Introduction to Lambda Calculus

Maciek Makowski

Very theoretical talk. Lamba calculus is pure math or even more theoretical, pure theoretical informatics, but it can be made a complete programming language with some thinking. It can be used for dealing with issues like computability. Many nice proofs are possible. The theoretical essence of functional programming languages is there. Some key words: „Church Rosser Theorem“, „Programming with Lambda-Calculus“, „numbers as lambda expressions“ (church encoding), „y combinator“, „fixed point combinator“, „lambda cube“, „fourth dimension for Subtypes“, ….
Very small language, great for proofs, not relevant or applicable for practical purposes.

State of the Typelevel

Lars Hupel

Typelevel is inpired by Haskell. Libraries by them are scalaz, shapeless, spire, scalaz-stream, monocle and more.
We should strive to get correct programs and optimize where the needs arises.
The JVM integers are not good. Think of the silent overflow. Floats (float and double) are good for numerical mathematicians and scientists with knowledge in this area, who can deal with error propagation an numerical inaccuracy.
Off course numbers can be seen as functions, like this:
$x=f(.)$ mit $\bigwedge_{n \in \Bbb N: n>0} \frac{f(n)-1}{n} < x < \frac{f(n)+1}{n}$ Equality of real numbers cannot be decided in finite time. What is "Costate command coalgebra"? Monocle provides "lenses" and similar stuff known from Haskell... Good binary serialization formats are rare in the JVM world. How should the fear of scalaZ and monads be overcome? Remember: "A monad is a monoid in the category of endofunctors. So what is the problem?" as could be read on Bodil Stokke’s T-shirt.

Slick: Bringing Scala’s Powerful Features to Your Database Access

Rebecca Grenier

Slick is a library that generates and executes SQL queries. The conceptional weaknesses of JPA and Hibernate are avoided.
It has drivers for the five major DBs (PostgreSQL, mySQL/mariaDB, Oracle, MS-SQL-Server and DB2) and some minor DBs, but it is not free for the three commercial DBs.
Inner and outer joins are possible and can be written in a decent way.
With database dictionaries slick is now even able to generate code. Which I have done, btw. a lot using perl scripts running on the DDL-SQL-script. But this is better, off course…

Upcoming in Slick 2.2

Jan Christopher Vogt

Monads haunt us everywhere, even here. Time to learn what they are. I will be giving a talk in the Ruby-on-Rails user group in Zürich, which will force me to learn it.
Here they come: monadic sessions….
Sessions in conjunction with futures are the best guarantee for all kinds of nightmares, because the SQL is sometimes executed when the session is no longer valid or the transaction is already over. When dealing with transactional databases a lot of cool programming patterns become harder. Just think of the cool java guys who execute stuff by letting a EJB-method return an instance of an inner class with the DB-session implicitely included there and calling a method which via JPA indirectly and implicitely does DB-access long after the EJB-method is over. Have fun when debugging this stuff. But we know about it and address it here.
At least Slick is theoretically correct, other than JPA which I conject to be theoretically incorrect, apart from the shortcomings of the concrete implementations.
Several statements can be combined with andThen or a for-comprehension. Be careful, by default this uses separate sessions and transactions, with very funny effects. But threads and sessions are expensive and must not be withheld during non-running non-SQL-activities by default. Reactiveness is so important. Futures and thread pools look promising, but this fails miserably when we have blocking operations involved, that will occupy our threads for nothing.
We would like to have assynchronous SQL-access, which can be done on DB- and OS-level, but JDBC cannot. So we have to work around on top of JDBC. Apart from using a reasonably low number of additional threads this approach seems to be viable.
Statically type checked SQL becomes possible in the future.

No more Regular Expressions

Phil Wills

I love the regex of Perl. Really. So why do effort to give up something so cool, even in non-perl-languages?
It is not as bad as it sounds. We retain regular expressions as a concept, just do not call them like that (for marketing reasons I assume) and write them differently. Writing them as strings between // is very natural in Perl, but it breaks the flow of the language in Scala. A typical programmatical scala-like approach is more natural and more type safe. And more robust in case of errors. org.paraboiled2 can be used. Capture is unfortunately positional, unlike in newer Perl-regex, where captures can be named. But it hurts less here.

Scala eXchange – Q&A Panel

Jon Pretty, Kingsley Davies, Lars Hupel, Martin Odersky, and Miles Sabin

Interesting discussions…

Why Scala is Taking Over the Big Data World

Dean Wampler

‚“Hadoop“ is the „EJB“ of our time.‘
MapReduce is conceptionally already functional programming. So why use Java and not Scala?
Some keywords: „Scalding“, „Storm“, „Summing bird“, „Spark“.
Scala can be more performant than python, which is so popular in this area, but migration has to be done carefully.

Case classes a la carte with shapeless, now!

Miles Sabin

Example: tree structure with backlinks. Hard to do in strict immutabilty. Shapeless helps.

Reactive Programming with Algebra

André Van Delft

Algebra can be fun and useful for programming. Algebraic interpretations were introduced.
Page is
Algebra of communicationg processes. It is very powerful and can even be applied to other targets, for example operation of railroad systems.
Every program that deals with inpout is in its way a parser. So ideas from yacc and bison apply to them.

High Performance Linear Algebra in Scala

Sam Halliday

Lineare Algebra has been addressed extremely well already, so the wheel should not be reinvented.
TL;D, Netflix and Breeze.
Example for usage of that stuff: Kalman Filter.
netlib has reference implementation in Fortran, a well defined interface and a reliable set of automatic tests. How do we take this into the scala world?
Fortran with C-Wrapper for JNI. (cblas)
compile Fortran to Java. really.
Alternate implementations of the same test suite in C.
High-Performance is not only about speed and memory alone, but about those under the given requirements concerning correctness, precision and stability.
Hardware is very interesting. The CPU-manufacturers are talking with the netlib team.
Can GPU be used? Off course, but some difficulties are involved, for example transfer of data.
FPGA? maybe soon? Or something like GPU, without graphics and operating on the normal RAM?
We will see such stuff working in the future.

An invitation to functional programming

Rúnar Bjarnason

Referential transparency, something like compatibility with the memoize pattern.
Pure functions…
Comprehensiveness.. The all time promise, will it be kept this time?
Functional programming is not good for the trenches of real life project, but for getting out of the trenches. This should be our dream. Make love not war, get rid of trenches…

Building a Secure Distributed Social Web using Scala & Scala-JS

Henry Story

Spargl is like SQL for the „semantic web“.
Developed with support from Oracle.
We can have relativiity of of truth while retaining the absolute truth. The speech was quite philosophical, in a good way.
Graphs can be isomorphic, but have a different level of trust, depending on where the copy lies.
Linked data protocol becomes useful.
How is spam and abuse avoided? WebID?
We are not dealing with „Big Data“ but with massively parallel and distributed „small data“.

TableDiff – a library for showing the difference between the data in 2 tables

Sue Carter

What is the right semantics for a diff?
What do we want to see? How are numbers and strings compared when occurring in fields?
Leave timestamps that obviously differ but do not carry much information out.

Evolving Identifiers and Total Maps

Patrick Premont

Idea is to have a map where get always returns something non-null. Smart type concepts avoid the compilation of a get call that would not return something.
Very interesting idea, but I find it more useful as theoretical concept rather than for practical purposes. The overhead seems to be big.


Overall it was a great conference.

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Devoxx 2014 in Belgium

In 2014 I have visited the Devoxx conference in Antwerp in Belgium.

Here are some notes about it:

What is Devoxx?

  • Devoxx ist a conference organized by the Belgian Java User Group.
  • Belgium is trilingual (French, Flemish and German), but the conference is 100% in English.
  • The location is a huge cinema complex, which guarantees for great sound, comfortable seats and excellent projectors. It is cool.
  • 8 tracks, overflow for keynotes
  • Well organized (at least this year), more fun than other conferences…
  • sister conferences:
    • Devoxx FR
    • Devoxx PL
    • Devoxx UK
    • Voxxed (Berlin, Ticino,….)

Topics & main Sponsors

  • Java / Oracle
  • Android / Oracle
  • Startups, Business, IT in enterprises / ING-Bank
  • Java-Server, JBoss, Deployment / Redhat
  • JVM-languages
  • Web
  • SW-Architecture
  • Security
  • Whatever roughly fits into these lines and is considered worth being talked about by the speaker and the organizers…

These are some of the talks that I have attended:

Scala and Java8

  • Many conceptional features of Scala have become available in Java 8 with lambdas.
  • Problem: different implementation and interoperability between Java and Scala.
  • Development of Scala will make lambdas of Scala and Java interoperabel.


  • Concept from category theory. (5% of mathematicians do algebra, 5% of algebraians do category theory, but this very abstract and very theoretical piece of math suddenly becomes interesting for functional programming. Off course our functional programming world lacks the degree of infiniteness that justifies the theory at all, but concepts can be applied anyway)
  • Monoid (+, *, concat,…)
  • Functor
  • Monad
  • Wikipedia de

  • (T, \eta, \mu)
  • example: List with a functor F: (A\rightarrow B)\rightarrow (List[A]\rightarrow List[B])
    \mu is flatten: List[List[A]]\rightarrow List[A]; \eta: A\rightarrow List[A]

Probability & Decisions

  • Example: Software for automatic steering of house infrastructure
  • Heuristics and probability theory
  • False positives / false negatives: what hurts? (usually both)
  • Very good explanation of probability theory and its use


  • Clojure is another JVM-language
  • It is a Lisp-Dialekt, recognizable by its source having an abundance of opening and closing parentheses: (+ (* 3 4) (* 5 6))…
  • strong support for functional programming.
  • Dynamically typed (for us: Just think of everything being declared as „Object“ and implicit casts being performed prior to method calls.
  • After Java itself, Scala, Groovy and Javascript it appears to me to be the fifth most common JVM-language


  • „No one at Google uses MapReduce anymore“
  • Google has replaced it with more general and more performance sensitive concepts and implementations.
  • Optimized: save steps, combine them etc.
  • Can be used as cloud service (Cloud Dataflow)

Key Note ING

  • ING considers itself to be an „open bank“
  • Not the money is lieing around openly for burglers to play with it, but they claim to be open for new ideas.
  • Mobile app is the typical interface to the bank.
  • IT has a lot of influence („IT driven business“)
  • Feasability from the IT side is considered important
  • Agile Prozesses (Scrum) vs. Enterprise IT
  • IT has slowly moved to these agile processes.
  • „Enterprise IT is what does not work“

Material Design

  • GUI-Design with Android and Web Material Design
  • Visual ideas available for both platforms
  • Polymer design for Web

SW-Architecture with Spring

  • Spring 4.1
  • „works with WebSphere“
  • DRY
  • Lambda from Java8 can simplify many APIs out of the box by just replacing one-method anonymous and inner classes.
  • Generic Messaging Interface (wasn’t JMS that already???)
  • Caching, be careful when testing, but can be disabled.
  • Test on
  • Spring works well with Java. Also with Groovy, which comes from the same shop as spring. Combination with Scala „experimental“


  • High-Level testing-Framework
  • Uses Java8-Features (Lambda etc.)
  • Description in natural language.
  • Failure-messages are human readable
  • Like Cucumber…
  • Source of randomness can be configured. This is very important for monte-carlo-testing, simulations and the like.

Builtin Types of Scala and Java

  • In Java we find „primitive types“ (long, int, byte, char, short, double,…)
  • Probleme with arithmetic with int, long & Co: Overflow happens unnoticed
  • With float and double Rounding errors
  • With BigInteger, BigDecimal, Complex, Rational error prone, clumpsy and unreadable syntax.
  • In Scala we can write a=b*c+d*e even for newly defined numerical types.
  • Remark: Oracle-Java-guys seem to consider the idea of operator overloading for numerical types more interesting than before, as long as it is not used for multiplying exceptions with collections and the like.
  • Spire library

Future of Java (9, 10, …)

Part I

  • Q&A-meeting (questions asked via twitter)
  • Numerical types are in issue. That primitive types behave as they do and are kind of the default won’t change.
  • Generics and type erasure (where is the problem)?
  • Jigsaw vs. Jars vs. OSGi still open how that will fit together, but jar is there to stay.
  • Jigsaw repository: Could well be located with maven central. Oracle does not work in such a way that this being hosted directly by Oracle is likely to happen, if third party software is there as well.

Part II

  • Benchmarking with Java is hard because of hot spot optimization
  • JMH is a good tool
  • New ideas are always hard to introduce because of the requirement of remaining compatible with old versions.
  • Java might get a „repl“ some day, like irb for Ruby…

Part III

  • Collection literals (promised once for Java 7!!!) did not make it into Java 8, unlikely for Java 9
  • With upcoming value types this might be more reasonable to find a clean way for doing that.
  • For Set and List somthing like
    new TreeSet(Arrays.asList(m1, m2, m3,…., mn))
    works already now
  • For maps something like a pair would be useful. Tuples should come and they should be based on value types. The rest remains as an exercise for the reader.

Part IV

  • Tail-Recursion can now be optimized in an upcoming version.
  • Because of the security-manager, that analyzed stacktraces this was impossible for a long time. (weird!!!)
  • C and Lisp have been doing this for decades now…
  • Statement: Generics are hard, but having understood them once they become easy. So keep trying….
  • Covarianz und Contravarianz (Bei Array falsch gelöst)

Part V

  • Arrays 2.0: indexing with long could become an issue. Some steps towards list, but with array syntax. (studies and papers only)
  • Lists have two extreme implementations: ArrayList and LinkedList. We would love to see more „sophisticated“ Lists, maybe some hybrid of both
  • Checked exceptions: critical issue, it was a problem with generics and lambda. And way too many exceptions are checked, just think of whatever close()-methods can throw, that should not be checked.

Semantic source code analysis

  • Useful for high level testing tools
  • Static and dynamic analysis
  • Dataflow analysis: unchecked data from outside, think of SQL-injection, but also CSS, HTML, JavaScript, JVM languages and byte code

Functional ideas in Java


  • Functions or methods are „first class citizens“
  • Higher order functions (C could that already)
  • Closures
  • Immutability (function always returns the same result)
  • „lazy“-constructions can be possible though
  • For big structures we always have the question of immutability vs. performance
  • But functional is much more thread-friendly

50 new things in Java8

Part I

  • Lambda (see below)
  • Streams (see below)
  • Default implementations in interfaces
  • Date/Time (loke Joda time)
  • Optional (better than null)
  • Libraries can work with lambda
  • Parallel (use with care and only when needed and useful)

Part II

  • String.join()
  • Something like „find“ in Unix/Linux
  • Writing comparators is much easier
  • Maps of Maps, Maps of Collections easier
  • Sorting is better: quicksort instead of mergesort, can be parallelized

Groovy for Android

  • Problem with JVM languages other than Java: library has to be included in each app. 🙁
  • Solution: jar optimization tool helps
  • Second problem: dynamic languages have to be compiled on demand on the device
  • Solution: „static“ programming, dynamic features possible but not performing well


  • Lambdas are anonymous functions
  • Idea given: interface XY with one method uvw()
  • Instead of

    XY xy = new XY() {
    public long uvw(long x) { return x*x }

    XY xy = x -> x*x;
  • shorter, more readable, easier to maintain, interface becomes superfluous in many cases.
  • Closure means that final variables from the surrounding context can be included
  • Instance methods can be seen as closures also, the include the instance in a closure like way.


  • Streams are somewhere in the vicinity of Collection, Iterable, Iterator and the like, but something new.
  • They have methods that allow a function to be applied on all elements
  • Elegant for programming stuff like
    • Sum
    • Product
    • Maximum
    • Minimum
    • First / last / any element with certain property
    • all elements with a certain property
    • all transformed Elements…
  • It turns out to be a wise decision to make it different from Iterable, Iterator, Collection,… and rather provide wrapping capabilities where needed.


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Visit to Scala Days in Berlin 2014


Around mid of June 2014 I have been visiting the Scala Days in Berlin. Like usual these events contain a lot of speeches, which were distributed in four tracks, apart from the key notes. The event location was a cinama, like the Devoxx in Antwerp, but this time one that has been transformed to something else many years ago, but good projectors were available. Major topics where issues about compiler construction which is a hard task, but looked at with the right functional perspective it can be derived from the simple task of writing an interpreter. This helps understanding language constructs in Scala, but the idea was applied to many other areas as well, for example for compiling and optimizing SQL queries and for analyzing source code.

Another major topic was „streams“, which can be useful for web services. Other than traditional web services which usually receive the whole request before starting to process it, concepts where discussed for dealing with large requests whose size is painful or impossible to keep at once in memory or who are even unlimited in size. These can also be applied to websockets. This demands processing data as soon as useful parts have arrived.

Another minor, but very interesting topic was development of Android apps with Scala. The commonly known approach is off course Scaloid, but an alternative, Macroid, was presented. It looked quite promising, because it allows to write nice Android apps with less code. A major worry is that scala apps consume too much memory due to their additional libraries. Because Scala uses its own libraries on top of the usual preinstalled Java libraries which are about 5 MB in size, this can easily anihilate the attractiveness of Scala for modern smart phone development, unless we assume rooted devices which have the Scala libs preinstalled. But that would seriously limit the scope of the app. This is not as bad as it sounds, because the build process contains one step in which unnecessary classes are removed, so that we only install what is really needed. When going as crazy as running Akka on the cell phone it becomes quite a challenge to configure this step because Akka uses a lot of reflection and so all these reflective entry points need to be configured, leaving a wide door open for bugs that occur at runtime when some class is not found.

API design was another interesting talk. Many ideas were quite similar to what I have heard in a API design traing for Perl by Damian Conway a couple of years ago, but off course there are many interesting Scala specific aspects to the topic. It is surprisingly hard to obtain binary compatibility of classes and this even forces to ugly compromises. So always recompiling everything looks tempting, but is not always reasonable. So ugly compromises remain part of our world, even when we are working with Scala.

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Devoxx 2013 Part 2

During the time from 2013-11-13 to 2013-11-15 I have been attending the Devoxx-conference in Antwerp in Belgium.
Most of the speeches I have been listening too were just great, like for example:

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