Scala Days 2018

In 2018 I visited Scala Days in Berlin with this schedule. Other than in previous years I missed the opening keynote, which is traditionally on the evening before the main conference starts, because this is not so well compatible with my choice of traveling with a night train, especially because I did not want to miss more than two days of my current project.

I might provide Links to Videos of the talks, if they become available, including the interesting keynote that I have missed.

So I did visit the following talks on the first full day:

And on the second full day:


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ScalaUA 2018

About a week ago I visited Scala UA in Kiev.

This was the schedule.

It was a great conference once again, as it was already in 2017 and I really enjoyed everything, including the food, which was great again… 🙂

I listened to the following talks on the first day:

And I gave this talk:

On the second day I listened to the following talks:

  • Advanced Patterns in Asynchronous Programming, Michael Arenzon & Assaf Ronen
  • Akka: Actors Design And Communication Techniques, Alex Zvolinskiy
  • Monad Stacks or: How I Learned to Stop Worrying and Love the Free Monad, and other stories, Harry Laoulakos
  • Scala on Wire: How event streams help us build Android apps, Maciej Gorywoda
  • Purely functional microservices with http4s and doobie, Jasper van Zandbeek
  • Tame Your Data with Reactive Streams and Monix, Jacek Kunicki
  • Future and issues of the Scala Ecosystem, Panel Discussion
  • Roll your own Event Sourcing, Lina Krutulytė-Kriščiūnė

And I gave this talk:

As always there was a lot of inspiration coming from the talks and a lot worth exploring in future posts. So there will be Scala posts once in a while, as in the past…


  • Scala Days 2018
  • Scala UA 2017
  • Scala UA (official page)
  • NoSQL
  • Scala
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Scala Exchange 2017

I have visited Scala Exchange („#ScalaX“) in London on 2017-12-14 and 2017-12-15. It was great, better than 2015 in my opinion. In 2016 I missed Scala Exchange in favor of Clojure Exchange.

This time there were really many talks about category theory and of course its application to Scala. Spark, Big Data and Slick were less heavily covered this time. Lightbend (former Typesafe), the company behind Scala, did show some presence, but less than in other years. But 800 attendees are a number by itself and some talks about category theory were really great.

While I have always had a hard time accepting why we need this „Über-Mathematics“ like category theory for such a finite task as programming, I start seeing its point and usefulness. While functors and categories provide a meta layer that is actually accessible in Scala there are actually quite rich theories that can even be useful when constrained to a less infinite universe. This helps understanding things in Java. I will leave details to another post. Or forget about it until we have the next Scala conference.

So the talks that I visited were:

  • Keynote: The Maths Behind Types [Bartosz Milewski]
  • Free Monad or Tagless Final? How Not to Commit to a Monad Too Early [Adam Warski]
  • A Pragmatic Introduction to Category Theory [Daniela Sfregola]
  • Keynote: Architectural patterns in Building Modular Domain Models [Debasish Ghosh]
  • Automatic Parallelisation and Batching of Scala Code [James Belsey and Gjeta Gjyshinca]
  • The Path to Generic Endpoints Using Shapeless [Maria-Livia Chiorean]
  • Lightning talk – Optic Algebras: Beyond Immutable Data Structures [Jesus Lopez Gonzalez]
  • Lightning Talk – Exploring Phantom Types: Compile-Time Checking of Resource Patterns [Joey Capper]
  • Lightning Talk – Leave Jala Behind: Better Exception Handling in Just 15 Mins [Netta Doron]
  • Keynote: The Magic Behind Spark [Holden Karau]
  • A Practical Introduction to Reactive Streams with Monix [Jacek Kunicki]
  • Building Scalable, Back Pressured Services with Akka [Christopher Batey]
  • Deep Learning data pipeline with TensorFlow, Apache Beam and Scio [Vincent Van Steenbergen]
  • Serialization Protocols in Scala: a Shootout [Christian Uhl]
  • Don’t Call Me Frontend Framework! A Quick Ride on Akka.Js [Andrea Peruffo]
  • Keynote: Composing Programs [Rúnar Bjarnason]
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Devoxx 2017

I was lucky to get a chance to visit Devoxx in Antwerp the sixth time in a row. As always there were interesting talks to listen to. Some issues that were visible across different talks:

Java 9 is now out and Java 8 will soon go into the first steps of deprecation. The step of moving to Java 9 is probably the hardest in the history of Java. There were features in the past that brought very significant changes, but they were usually kind of optional, so adoption could be avoided or delayed. Java 9 brings the module system and a new level of abstraction in that classes of modules can be made public to other modules selectively or globally. Otherwise they can be by themselves declared as public, but only be visible within the module. This actually applies to classes of the standard library, that were always declared as being private, but that could not be efficiently hidden away from external usage. Now they suddenly do not work any more and a lot of software has some difficulty and needs to be adjusted to avoid these internal classes. Beyond that a lot of talks were about Java 9, for example also covering somewhat convenient methods for writing constant collections in code. Future releases will follow a path that is somewhat similar to that of Perl 5. Releases will be created roughly every half year and will include whatever is ready for inclusion at that time. Some releases will be supported for a longer time than others.

In the arena of non-Java JVM-languages the big winner seems to be Kotlin, while Groovy, Clojure, JRuby and Ceylon where not visible at the conference. Scala has retained its position as an important JVM language besides Java at this conference. The rise of Kotlin may be explained by the fact that Idea (IntelliJ) has become much more important as IDE than Eclipse and Netbeans, which already brings Kotlin onto every JVM-language-developer’s desktop. And Google has moved from Eclipse to Idea as recommended and supported IDE for Android-development and is now officially supporting Kotlin besides Java as language for Android-development. There were heroic efforts to do development in Scala, Clojure, Groovy for Android without support from Google, which is quite possible, but having to deploy the libraries with each app instead of having them already on the phone is a big disadvantage. The second largest mobile OS has added support for Swift as an alternative to Objective C and Swift and Kotlin are different languages, but they are sufficiently similar in terms of concepts and possibilities to ease development of Apps targeting the two most important mobile system platforms in mixed teams at least a bit. And Kotlin gives developers many of the cool and interesting features of Scala, while remaining a bit easier to learn and to understand, because some of the most difficult parts of Scala are left out. Anyway, Scala is not yet heavily challenged by Kotlin and remains important and I think that Clojure and JRuby and Groovy retain their importance and live in somewhat differenct niches than Scala and Kotlin. I would think that they are just a bit too small to be present on each Devoxx. Or it was just random effects about how much news there was about the languages and what kind of speeches had been proposed for them. On the other hand, I would assume that Ceylon has become a dead end, because it came out at the same time as Kotlin and tries to cover the same niche. It is hard to stay important in the same niche with a strong winner.

Then there was of course security security security… Even more important than in the past.

And a lot more…

I listened to the following talks:
Wednesday, 2017-11-08

Thursday, 2017-11-09

Friday, 2017-11-10


Previous years:

Btw. I always came to Devoxx by bicycle, at least part of the way…

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ScalaUA 2017

About a month ago I visted the conference ScalaUA in Kiev.

This was the schedule.

It was a great conference and I really enjoyed everything, including the food, which is quite unusual for an IT-conference.. 🙂

I listened to the following talks:
First day:

  • Kappa Architecture, Juantomás García Molina
  • 50 shades of Scala Compiler, Krzysztof Romanowski
  • Functional programming techniques in real world microservices, András Papp
  • Scala Refactoring: The Good the Bad and the Ugly, Matthias Langer
  • ScalaMeta and the Future of Scala, Alexander Nemish
  • ScalaMeta semantics API, Eugene Burmako

I gave these talks:

  • Some thoughts about immutability, exemplified by sorting large amounts of data
  • Lightning talK: Rounding

Day 2:

  • Mastering Optics in Scala with Monocle, Shimi Bandiel
  • Demystifying type-class derivation in Shapeless, Yurii Ostapchuk
  • Reactive Programming in the Browser with Scala.js and Rx, Luka Jacobowitz
  • Don’t call me frontend framework! A quick ride on Akka.Js, Andrea Peruffo
  • Flawors of streaming, Ruslan Shevchenko
  • Rewriting Engine for Process Algebra, Anatolii Kmetiuk

Find recording of all the talks here:

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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 of 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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Almost every serious programming language has to deal with database access, if not out of love, then at least out of practical necessity.

The theoretical background of a functional programming language is somewhat hostile to this, because pure functional langauges tend to dislike state and a database has the exact purpose to preserve state for a long time. Treating the database as somewhat external and describing its access with monads will at least please theoretical purists to some extent.

In case of Scala things are not so strict, it is allowed to leave the purely functional path where adequate. But there are reasons to follow it and to leave it only in well defined, well known, well understood and well contained exceptions… So the database itself may be acceptable.

Another intellectual and practical challenge is the fact that modern Scala architectures like to be reactive, like to uncouple things, become asynchronous. This is possible with databases, but it is very unusual for database drivers to support this. And it is actually quite contrary to the philosophy of database transactions. It can be addressed with future database drivers, but I do not expect this to be easy to use properly in conjunction with transactions.

It is worthwhile to think about
immutability and databases.
For now we can assume that the database is there and can be used.

So the question is, why not integrate existing and established persistence frameworks like JPA, Hibernate, Eclipslink and other OR-mapping-based systems into Scala, with Scala language binding?

Actually I am quite happy they did not go this path. Hibernate is broken and buggy, but the generic concept behind it is broken in my opinion. I do not think that it is theoretically correct, especially if we should program with waterproof transactions and actually defeat them by JPA-caching without even being aware of it? But for practical purposes, I actually doubt that taming JPA for non trivial applications is really easier than good old JDBC.

Anyway, Scala took the approach of building something in the lines of JDBC, but making it nicer. It is called Slick, currently Slick 3. Some links:
* Slick
* Slick 3.1.1
* Documentation
* Github
* Assynchronous DB access
* Recording of the Slick Workshop at ScalaX

What Slick basically does is building queries using Scala language. It does pack the results into Scala structures. Important is, that the DB is not hidden. So we just do the same as with JDBC, but in a more advanced way.

This article is inspired by my visit to Scala X.

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How to create ISO Date String

It is a more and more common task that we need to have a date or maybe date with time as String.

There are two reasonable ways to do this:
* We may want the date formatted in the users Locale, whatever that is.
* We want to use a generic date format, that is for a broader audience or for usage in data exchange formats, log files etc.

The first issue is interesting, because it is not always trivial to teach the software to get the right locale and to use it properly… The mechanisms are there and they are often used correctly, but more often this is just working fine for the locale that the software developers where asked to support.

So now the question is, how do we get the ISO-date of today in different environments.

Linux/Unix-Shell (bash, tcsh, …)

date "+%F"


\def\dayiso{\ifcase\day \or
01\or 02\or 03\or 04\or 05\or 06\or 07\or 08\or 09\or 10\or% 1..10
11\or 12\or 13\or 14\or 15\or 16\or 17\or 18\or 19\or 20\or% 11..20
21\or 22\or 23\or 24\or 25\or 26\or 27\or 28\or 29\or 30\or% 21..30
\def\monthiso{\ifcase\month \or
01\or 02\or 03\or 04\or 05\or 06\or 07\or 08\or 09\or 10\or 11\or 12\fi}

This can go into a file isodate.sty which can then be included by \include or \input Then using \todayiso in your TeX document will use the current date. To be more precise, it is the date when TeX or LaTeX is called to process the file. This is what I use for my paper letters.


(From Fritz Zaucker, see his comment below):

\usepackage{isodate} % load package
\isodate % switch to ISO format
\today % print date according to current format



On Oracle Docs this function is documented.
It can be chosen as a default using ALTER SESSION for the whole session. Or in SQL-developer it can be configured. Then it is ok to just call


Btw. Oracle allows to add numbers to dates. These are days. Use fractions of a day to add hours or minutes.


(From Fritz Zaucker, see his comment):

select current_date;
—> 2016-01-08

select now();
—> 2016-01-08 14:37:55.701079+01


In Emacs I like to have the current Date immediately:

(defun insert-current-date ()
"inserts the current date"
(let ((x (current-time-string)))
(concat (substring x 20 24)
(cdr (assoc (substring x 4 7)
(let ((y (substring x 8 9)))
(if (string= y " ") "0" y))
(substring x 9 10)))))
(global-set-key [S-f5] 'insert-current-date)

Pressing Shift-F5 will put the current date into the cursor position, mostly as if it had been typed.

Emacs (better Variant)

(From Thomas, see his comment below):

(defun insert-current-date ()
"Insert current date."
(insert (format-time-string "%Y-%m-%d")))


In the Perl programming language we can use a command line call

perl -e 'use POSIX qw/strftime/;print strftime("%F", localtime()), "\n"'

or to use it in larger programms

use POSIX qw/strftime/;
my $isodate_of_today = strftime("%F", localtime());

I am not sure, if this works on MS-Windows as well, but Linux-, Unix- and MacOS-X-users should see this working.

If someone has tried it on Windows, I will be interested to hear about it…
Maybe I will try it out myself…

Perl 5 (second suggestion)

(From Fritz Zaucker, see his comment below):

perl -e 'use DateTime; use 5.10.0; say DateTime->now->strftime(„%F“);‘

Perl 6

(From Fritz Zaucker, see his comment below):




This is even more elegant than Perl:

ruby -e 'puts"%F")'

will do it on the command line.
Or if you like to use it in your Ruby program, just use

d =
s = d.strftime("%F")

Btw. like in Oracle SQL it is possible add numbers to this. In case of Ruby, you are adding seconds.

It is slightly confusing that Ruby has two different types, Date and Time. Not quite as confusing as Java, but still…
Time is ok for this purpose.

C on Linux / Posix / Unix


main(int argc, char **argv) {

char s[12];
time_t seconds_since_1970 = time(NULL);
struct tm local;
struct tm gmt;
localtime_r(&seconds_since_1970, &local);
gmtime_r(&seconds_since_1970, &gmt);
size_t l1 = strftime(s, 11, "%Y-%m-%d", &local);
printf("local:\t%s\n", s);
size_t l2 = strftime(s, 11, "%Y-%m-%d", &gmt);
printf("gmt:\t%s\n", s);

This speeks for itself..
But if you like to know: time() gets the seconds since 1970 as some kind of integer.
localtime_r or gmtime_r convert it into a structur, that has seconds, minutes etc as separate fields.
stftime formats it. Depending on your C it is also possible to use %F.


import java.util.Date
import java.text.SimpleDateFormat
val s : String = new SimpleDateFormat("YYYY-MM-dd").format(new Date())

This uses the ugly Java-7-libraries. We want to go to Java 8 or use Joda time and a wrapper for Scala.

Java 7

import java.util.Date
import java.text.SimpleDateFormat

String s = new SimpleDateFormat("YYYY-MM-dd").format(new Date());

Please observe that SimpleDateFormat is not thread safe. So do one of the following:
* initialize it each time with new
* make sure you run only single threaded, forever
* use EJB and have the format as instance variable in a stateless session bean
* protect it with synchronized
* protect it with locks
* make it a thread local variable

In Java 8 or Java 7 with Joda time this is better. And the toString()-method should have ISO8601 as default, but off course including the time part.


This is quite easy to achieve in many environments.
I could provide more, but maybe I leave this to you in the comments section.
What could be interesting:
* better ways for the ones that I have provided
* other databases
* other editors (vim, sublime, eclipse, idea,…)
* Office packages (Libreoffice and MS-Office)
* C#
* F#
* Clojure
* C on MS-Windows
* Perl and Ruby on MS-Windows
* Java 8
* Scala using better libraries than the Java-7-library for this
* Java using better libraries than the Java-7-library for this
* C++
* Python
* Cobol
* JavaScript
* …
If you provide a reasonable solution I will make it part of the article with a reference…
See also Date Formats

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Scala Exchange 2015

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

I visited the following events:

Conversion of ASCII-graphics to PNG or JPG

Images are usually some obscure binary files. Their most common formats, PNG, SVG, JPEG and GIF are well documented and supported by many software tools. Libraries and APIs exist for accessing these formats, but also a phantastic free interactive software like Gimp. The compression rate that can reasonably be achieved when using these format is awesome, especially when picking the right format and the right settings. Tons of good examples can be found how to manipulate these image formats in C, Java, Scala, F#, Ruby, Perl or any other popular language, often by using language bindings for Image Magick.

There is another approach worth exploring. You can use a tool called convert to just convert an image from PNG, JPG or GIF to XPM. The other direction is also possible. Now XPM is a text format, which basically represents the image in ASCII graphics. It is by the way also valid C-code, so it can be included directly in C programms and used from there, when an image needs to be hard coded into a program. It is not generally recommended to use this format, because it is terribly inefficient because it uses no compression at all, but as intermediate format for exploring additional ways for manipulating images it is of interest.
An interesting option is to create the XPM-file using ERB in Ruby and then converting it to PNG or JPG.

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