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Scalania - learn Scala by examples

The project is to help you get started with Scala. It's also been used successfully to run Scala hack-a-thons in Warsaw, Poland - see Scalania webpage on meetup.

This is a sbt-based project with tests that are supposed to help people learn (and ultimately master) Scala while solving problems described in S-99: Ninety-Nine Scala Problems (package pl.japila.scalania.s99) and doing the exercises that accompany the Scala course Scala i programowanie funkcyjne or are part of the Project Euler (package pl.japila.scalania.euler).

The website of the meetings is scalania.pl.

How to get started with the project

  • Download and install the latest version of sbt.

  • In the directory where you downloaded (cloned) the scalania project, run sbt.

      jacek:~/oss/scalania
  $ sbt
  [info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
  [info] Loading project definition from /Users/jacek/oss/scalania/project
  [info] Set current project to scalania (in build file:/Users/jacek/oss/scalania/)
  >

  • Pick a problem to work on. There are quite a few in exercises/src/main/scala directory. Say, you chose pl.japila.scalania.s99.S99_P01. Run the corresponding test specification using ~exercises/testOnly *s99.P01* (the asterisks are important to denote a regular expression). Hint: Use [TAB] while in sbt.

      > ~exercises/testOnly *s99.P01*
  [info] P01Spec
  [info]
  [info] P01 solution should
  [info] x Find the last element of a list
  [error]    an implementation is missing (S99_P01.scala:4)
  [info]
  [info]
  [info] Total for specification P01Spec
  [info] Finished in 45 ms
  [info] 1 example, 1 failure, 0 error
  [error] Failed: Total 1, Failed 1, Errors 0, Passed 0
  [error] Failed tests:
  [error]         pl.japila.scalania.s99.P01Spec
  [error] (exercises/test:testOnly) sbt.TestsFailedException: Tests unsuccessful
  [error] Total time: 8 s, completed Nov 9, 2013 12:37:49 PM
  1. Waiting for source changes... (press enter to interrupt)

Make the test pass (make it green). In the above snippet pl.japila.scalania.s99.P01Spec fails because of an implementation is missing. That's exactly your assignment - to write the implementation.

In this case you'd have to write the implementation of pl.japila.scalania.s99.S99_P01 object.

  • Once the test gets green (the success shows up as a result of running it), you're almost done.

      [info] Formatting 1 Scala source {file:/Users/jacek/oss/scalania/}exercises(compile) ...
  [info] Compiling 1 Scala source to /Users/jacek/oss/scalania/exercises/target/scala-2.10/classes...
  [info] P01Spec
  [info]
  [info] P01 solution should
  [info] + Find the last element of a list
  [info]
  [info]
  [info] Total for specification P01Spec
  [info] Finished in 46 ms
  [info] 1 example, 0 failure, 0 error
  [info] Passed: Total 1, Failed 0, Errors 0, Passed 1
  [success] Total time: 13 s, completed Oct 22, 2013 11:31:20 PM
  2. Waiting for source changes... (press enter to interrupt)

Press Enter to interrupt.

Spoiler: There are a few solutions of the exercises that you could execute with answers/testOnly *s99.P01*. Just replace ~exercises with answers to kick it off.

  • In order to finish the exercises, run exercises/scalastyle to ensure high quality of your solutions that is manifested with Found 0 errors and Found 0 warnings in the output.

      > exercises/scalastyle
  Processed 29 file(s)
  Found 0 errors
  Found 0 warnings
  Finished in 1 ms
  [success] created: /Users/jacek/oss/scalania/exercises/target/scalastyle-result.xml
  [success] Total time: 0 s, completed Nov 9, 2013 8:44:50 PM

How to open the project in IntelliJ IDEA 13 (Cardea)

  • Install the sbt-idea plugin. Create ~/.sbt/0.13/plugins/idea.sbt file and add the following:

      // https://github.com/mpeltonen/sbt-idea
  resolvers += "Sonatype snapshots" at "http://oss.sonatype.org/content/repositories/snapshots/"

  addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.6.0-SNAPSHOT")

  • Run sbt gen-idea in the home directory of the scalania project.

      $ sbt gen-idea
  [info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
  [info] Loading project definition from /Users/jacek/oss/scalania/project
  [info] Set current project to scalania (in build file:/Users/jacek/oss/scalania/)
  [info] Creating IDEA module for project 'answers' ...
  [info] Resolving org.fusesource.jansi#jansi;1.4 ...
  [info] Creating IDEA module for project 'exercises' ...
  [info] Resolving org.fusesource.jansi#jansi;1.4 ...
  [info] Creating IDEA module for project 'scalania' ...
  [info] Resolving org.fusesource.jansi#jansi;1.4 ...
  [info] Excluding folder target
  [info] Created /Users/jacek/oss/scalania/.idea/IdeaProject.iml
  [info] Deleted existing library files
  [info] Created /Users/jacek/oss/scalania/.idea
  [info] Excluding folder /Users/jacek/oss/scalania/answers/target
  [info] Created /Users/jacek/oss/scalania/.idea_modules/answers.iml
  [info] Excluding folder /Users/jacek/oss/scalania/exercises/target
  [info] Created /Users/jacek/oss/scalania/.idea_modules/exercises.iml
  [info] Excluding folder /Users/jacek/oss/scalania/target
  [info] Created /Users/jacek/oss/scalania/.idea_modules/scalania.iml
  [info] Created /Users/jacek/oss/scalania/.idea_modules/exercises-build.iml
  [info] Created /Users/jacek/oss/scalania/.idea_modules/scalania-build.iml

  • Open the project in IntelliJ IDEA. Have fun!

How to contribute

A quite productive approach to master Scala is to further extend the project with new tests that show what the language can offer.

git clone the scalania project and send pull requests on GitHub.

Please use topic branches when sending pull requests rather than committing directly to master in order to minimize unnecessary merge commit clutter.

  • Create a topic branch and switch to it. Say, you want to work on the 100th problem in the Euler Project and the branch gets named euler_100.

      $ git checkout -b euler_100
  Switched to a new branch 'euler_100'

  • Do the work and git commit it.

  • git push origin euler_100

  • Send pull request using GitHub. It should automatically suggest you doing so when your branch has showed up.

  • (optional) Once the pull request's accepted, delete the branch from the remote repository git push origin :euler_100 and from the local repository git branch -d euler_100.

Tools used