scripting with Scala

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The need for regular expressions is real. Whenver I need to transform a set of text files it usually ends up with fumbling through the documentation of find command, zsh, and StackOverflow Perl questions. I would rather use Scala instead of muddling through Perl. It's really the matter of my familiarity than anything else.

For example, I now have over a hundred reStructuredText files that I want to convert into markdown. I first tried pandoc, and it looked mostly ok. As I was going through the details, however, I noticed that many of the code literals were not converting over as formatted. This is because they were formatted using either single ticks or using Interpreted Text. Preprocessing the text with a series of regex replacements should work.

sbt technology preview: auto plugins

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nescala 2014 day 2: 30 sbt plugins in 15 minutes

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Slides from nescala day 2 unconference:

I may have added a few more :)

learning Scalaz: nescala 2014

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Here are the slide decks and video for learning Scalaz talk:

learning Scalaz: day 21

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Added day 21 on html5 book.

learning Scalaz: day 20

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Added day 20 on html5 book.

learning Scalaz: day 19

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Added day 19 on the html5 book.

constraining class linearization (mixin order) in Scala

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Woke up early yesterday, so I started skimming @xuwei_k's override blog post. The topic was so intriguing, I got out of the bed and started translating it as the curious case of putting override modifier when overriding an abstract method in Scala. In there he describes the conundrum of providing the default instances to typeclasses by using Scalaz codebase as an example.

Here's a simplified representation of the problem:

trait Functor {
  def map: String
}
trait Traverse extends Functor {
  override def map: String = "meh"
}
sealed trait OneOrFunctor extends Functor {
  override def map: String = "better"
}
sealed trait OneOrTraverse extends OneOrFunctor with Traverse {
}
object OneOr {
  def OneOrFunctor: Functor = new OneOrFunctor {}
  def OneOrTraverse: Traverse = new OneOrTraverse {}
}

curious case of putting override modifier when overriding an abstract method in Scala

in

This is a translation of Scalaで抽象メソッドをoverrideする際にoverride修飾子を付けるべきかどうかの是非 by Kenji Yoshida (@xuwei_k), a Scalaz committer.

First, a quote from Programming in Scala, 2nd ed. p. 192:

Scala requires [override] modifier for all members that override a concrete member in a parent class. The modifier is optional if a member implements an abstract member with the same name.

In this post, we'll discuss this "The modififier is optional." Since overriding an existing method with implementation requires override modifier, and failure to do so would result to a compiler error, there's not much to talk about for that case. We'll focus on whether one should put override modifier or not in the case of overring an abtract method. I don't think there's going to be any difference in Scala version, but let's assume the latest stable 2.10.3.

sequencing tasks with sbt-sequential

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In this post, I will discuss the execution semantics and task sequencing in sbt 0.13. First we will cover the background, and then I will introduce a new experimental plugin sbt-sequential that adds sequential tasks.

background

Mark said:

The sbt model is to have your side effects be local to your task so that as long as dependencies are satisfied, the task can be executed whenever. The win is parallel by default and enabling faster builds in practice.

In other words, with sbt, the build definitions only define the dependencies between the tasks. The timing at which these tasks are triggered is automatically calculated by sbt. To understand this, we should first look at the execution semantics of a Scala code with side effects.

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