Dotty 0.4.0-RC1 Blog Post

docs/blog/_posts/2017-10-16-fourth-dotty-milestone-release.md

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+---
+layout: blog-page
+title: Announcing Dotty 0.4.0-RC1
+author: Allan Renucci
+authorImg: /images/allan.jpg
+date: 2017-10-16
+---
+
+Today, we are excited to release Dotty version 0.4.0-RC1. This release
+serves as a technology preview that demonstrates new language features
+and the compiler supporting them.
+
+If you’re not familiar with Dotty, it's a platform to try out new language concepts and compiler
+technologies for Scala. The focus is mainly on simplification. We remove extraneous syntax
+(e.g. no XML literals), and try to boil down Scala’s types into a smaller set of more fundamental
+constructors. The theory behind these constructors is researched in
+[DOT](https://infoscience.epfl.ch/record/215280), a calculus for dependent object types.
+You can learn more about Dotty on our [website](http://dotty.epfl.ch).
+
+<!--more-->
+
+This is our fourth scheduled release according to our [6-week release schedule](http://dotty.epfl.ch/docs/usage/version-numbers.html).
+The [previous technology preview](/blog/2017/09/07/third-dotty-milestone-release.html) improved
+stability and reliability.
+
+## What’s new in the 0.4.0-RC1 technology preview?
+
+### Rewritten REPL [#2991](https://github.com/lampepfl/dotty/pull/2991)
+The original Dotty REPL was a proof of concept hacked together
+from
+[an ancient version of the scalac REPL](https://github.com/lampepfl/dotty/pull/1082#issuecomment-183905504).
+It worked by creating Scala source files from the user input using string
+concatenation, this made it easy to adapt it for Dotty since it did not rely on
+the internals of scalac, but it was also fragile and hard to reason about.
+The [new REPL](https://github.com/lampepfl/dotty/pull/2991) instead works by
+manipulating ASTs (Abstract Syntax Trees), this is more robust and will make it
+easier to develop new features: we have already implemented auto-completion
+support (by reusing the APIs we had created for
+the [Dotty IDE](http://dotty.epfl.ch/docs/usage/ide-support.html)) and we have
+plans for displaying API documentation in the REPL.
+
+Note that the user interface of the REPL has not changed: like in the old REPL
+we use code adapted from the [Ammonite REPL](http://ammonite.io/#Ammonite-REPL)
+to provide syntax highlighting, multi-line editing, history, etc.
+
+### Scala 2.12 support [#2827](https://github.com/lampepfl/dotty/pull/2827)
+Since our first release, it has been possible to use Scala 2 libraries in a
+Dotty project as explained in the
+[dotty-example-project](https://github.com/smarter/dotty-example-project#getting-your-project-to-compile-with-dotty).
+Previously, we supported libraries compiled by Scala 2.11, but starting with this
+release we support Scala 2.12 instead. If your Dotty project has Scala 2
+dependencies this change should be transparent for you assuming all your
+dependencies have been published for 2.12.
+
+### Performance work
+Over the last few weeks, we started working on compilation speed with some good results:
+compiling [ScalaPB](https://github.com/dotty-staging/scalapb) is now 20% faster
+than with Dotty 0.3.0-RC2. You can follow along our progress on
+http://dotty-bench.epfl.ch/.
+
+
+## Trying out Dotty
+### Scastie
+[Scastie], the online Scala playground, supports Dotty.
+This is an easy way to try Dotty without installing anything.
+
+### sbt
+Using sbt 0.13.13 or newer, do:
+
+```
+sbt new lampepfl/dotty.g8
+```
+
+This will setup a new sbt project with Dotty as compiler. For more details on
+using Dotty with sbt, see the
+[example project](https://github.com/lampepfl/dotty-example-project).
+
+### IDE support
+It is very easy to start using the Dotty IDE in any Dotty project by following
+the [IDE guide](http://dotty.epfl.ch/docs/usage/ide-support.html).
+
+
+### Standalone installation
+Releases are available for download on the _Releases_
+section of the Dotty repository:
+[https://github.com/lampepfl/dotty/releases](https://github.com/lampepfl/dotty/releases)
+
+We also provide a [homebrew](https://brew.sh/) package that can be installed by running:
+
+```
+brew install lampepfl/brew/dotty
+```
+
+In case you have already installed Dotty via brew, you should instead update it:
+
+```
+brew upgrade dotty
+```
+
+## Let us know what you think!
+If you have questions or any sort of feedback, feel free to send us a message on our
+[Gitter channel](https://gitter.im/lampepfl/dotty). If you encounter a bug, please
+[open an issue on GitHub](https://github.com/lampepfl/dotty/issues/new).
+
+## Contributing
+Thank you to all the contributors who made this release possible!
+
+According to `git shortlog -sn --no-merges 0.3.0-RC2..0.4.0-RC1` these are:
+
+```
+   226  Martin Odersky
+   112  Felix Mulder
+   104  Nicolas Stucki
+    41  Allan Renucci
+    41  Guillaume Martres
+    33  liu fengyun
+     8  Olivier Blanvillain
+     4  Aggelos Biboudis
+     3  Dmitry Petrashko
+     2  Raymond Tay
+     2  esarbe
+     2  Enno Runne
+     1  Brandon Elam Barker
+     1  Raphael Bosshard
+     1  Jacob J
+     1  Aleksander Boruch-Gruszecki
+     1  Jim Van Horn
+     1  Matthias Sperl
+     1  Michal Gutowski
+```
+
+If you want to get your hands dirty and contribute to Dotty, now is a good time to get involved!
+You can have a look at our [Getting Started page for new contributors](http://dotty.epfl.ch/docs/contributing/getting-started.html),
+the [Awesome Error Messages](http://scala-lang.org/blog/2016/10/14/dotty-errors.html) project or some of
+the simple [Dotty issues](https://github.com/lampepfl/dotty/issues?q=is%3Aissue+is%3Aopen+label%3Aexp%3Anovice).
+They make perfect entry-points into hacking on the compiler.
+
+We are looking forward to having you join the team of contributors.
+
+## Library authors: Join our community build
+Dotty now has a set of widely-used community libraries that are built against every nightly Dotty
+snapshot. Currently this includes ScalaPB, algebra, scalatest, scopt and squants.
+Join our [community build](https://github.com/lampepfl/dotty-community-build)
+to make sure that our regression suite includes your library.
+
+To get started, see [https://github.com/lampepfl/dotty](https://github.com/lampepfl/dotty).
+
+
+[Scastie]: https://scastie.scala-lang.org/?target=dotty
+
+[@odersky]: https://github.com/odersky
+[@DarkDimius]: https://github.com/DarkDimius
+[@smarter]: https://github.com/smarter
+[@felixmulder]: https://github.com/felixmulder
+[@nicolasstucki]: https://github.com/nicolasstucki
+[@liufengyun]: https://github.com/liufengyun
+[@OlivierBlanvillain]: https://github.com/OlivierBlanvillain
+[@biboudis]: https://github.com/biboudis
+[@allanrenucci]: https://github.com/allanrenucci