https://twitter.github.io/scala_school/ko/basics.html
https://blog.outsider.ne.kr/945
http://docs.scala-lang.org/ko/tutorials/scala-for-java-programmers.html
http://euler.synap.co.kr/prob_list.php
http://blog.lgcns.com/211
method vs function
https://groups.google.com/forum/#!topic/scala-korea/dfkcfM5yM9M